Switchboards

A M E R I C A N

N A T I O N A L

S T A N D A R D

NECA 400-2007

Standard for

Installing and Maintaining Switchboards

®

Published by

National Electrical Contractors Association

NECA 400-2007 Standard for

Installing and Maintaining Switchboards An American National Standard

®

Published by


NECA 400-2007 Standard for

Installing and Maintaining Switchboards An American National Standard

®

Published by


NOTICE OF COPYRIGHT This document is copyrighted by NECA Reproduction of these documents either in hard copy or soft (including posting on the web) is prohibited Reproduction prohibited withoutt cop withou copyright yright permissi permission. on. For copyright copyright permis permission sion to to reproduc reproducee portions portions of this document document,, please contact NECA Standards & Safety at (301) 215-4546, or send a fax to (301) 215-4500. OR National Electrical Contractors Association 3 Bethes Bethesda da Metro Metro Center Center, Suit Suitee 1100 Bethesda, Bethes da, Maryland 20814 20814 (301) 657-3110 Organizations may obtain permission to reproduce a limited limited number of copies by entering entering into a license agreem agr eement ent.. Fo Forr inf inform ormati ation, on, co contac ntact: t: IHS 15 Iverness Way East Englewood, Englew ood, CO 80112-5704 80112-5704 or call 1-800-854-7179 (USA and Canada) (303) 397-7956 (International)

Table of Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iii 1.

Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.1 1.2

Products and Applications Included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Regulatory and Other Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

2.

Switchboard Receiving, Handling, and Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2.1 2.2 2.3

Receiving the Switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Handling the Switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Storing the Switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

3.

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14

Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Foundation Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 General Installation Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Installing Vertical Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Joining Switchboard Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Anchoring the Switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Installing Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Installing Interconnections Between Switchboard Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Ground Bus Splice Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Grounding and Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Busway Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Conduit Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Cable Pulling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Cable Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

4.

Pre-Energizing Checkout Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9

Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Insulation Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Current Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Circuit Breakers and Fusible Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Ground-fault Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Interconnections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Power Fuses and Control Power Disconnects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Clean-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Close-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

i



NECA 400

Recommended Practice for Installing and Maintaining Switchboards

5.

Energizing the Switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

6.

Switchboard Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

6.1 6.2 6.3 6.4 6.5 6.6

Routine Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 Safety Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 Cleaning and Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 Maintenance and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 Insulation Resistance Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Re-energizing Switchboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

7.

Adverse Circumstances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

7.1 7.2 7.3

Inspection Following a Short-Circuit or Ground-Fault Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Replacing a Switchboard Soaked by or Submerged in Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Inspecting and Re-energizing a Switchboard Sprayed or Splashed with Clean Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

8.

Recommended Torque Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

9.

Switchboard Insulation Resistance Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

10.

Operations and Maintenance Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Annex A: Reference Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24



ii

(This foreword is not a part of the standard)

Foreword

National Electrical Installation Standards ™ (NEIS®) are designed to improve communication among specifiers, purchasers, and suppliers of electrical construction services. They define a minimum baseline of quality and workmanship for installing electrical products and systems. NEIS are intended to be referenced in contract documents for electrical construction pro jects. The following language is recommended: Deadfront distribution switchboards rated 600 volts or less shall be installed and maintained in accordance with NECA 400, Standard for Installing and Maintaining Switchboards (ANSI). Use of NEIS is voluntary, and the National Electrical Contractors Association assumes no obligation or liability to users of this publication. Existence of a standard shall not preclude any member or nonmember of NECA from specifying or using alternate construction methods permitted by applicable regulations. The installation and maintenance practices recommended by this publication are intended to comply with the edition of the National Electrical Code® (NEC) in effect at the time of publication. Because they are quality standards, NEIS may in some instances go beyond the minimum safety requirements of the NEC. It is the responsibility of users of this standard to comply with state and local electrical codes when installing electrical products and systems.

Suggestions for revisions and improvements to this standard are welcome. They should be addressed to: NECA Standards & Safety 3 Bethesda Metro Center, Suite 1100 Bethesda, MD 20814 (301) 657-3110 telephone (301) 215-4500 fax www.neca-neis.org [email protected] To purchase NEIS, contact the NECA Order Desk at (301) 215-4504 tel, (301) 215-4500 fax, or [email protected] . NEIS can also be purchased in PDF format from www.neca-neis.org/standards. Copyright© 2007, National Electrical Contractors Association. All rights reserved. Unauthorized reproduction prohibited. National Electrical Installation Standards, NEIS, and the NEIS logo are trademarks of the National Electrical Contractors Association. National Electrical Code and NEC are registered trademarks of the National Fire Protection Association.

iii



Revision History NECA 400-1998

09/1998

NECA 400-2007

07/2007



iv

1. Scope

1.1

Products and Applications Included

This standard desribes installation procedures for deadfront distribution switchboards rated 600 volts or less. This standard also covers periodic routine maintenance procedures for switchboards, and special procedures to be used after adverse circumstances, such as a short circuit, ground-fault, or immersion in water.

1.2

Regulatory and Other Requirements

a) All information in this publication is intended to conform to the National Electrical Code (ANSI/NFPA 70). Installers should always follow the NEC, applicable state and local codes, manufacturer’s instructions, and contract documents.

b) Only qualified persons familiar with the construction and installation of motor control centers should perform the work described in this publication. It is recommended that all work be performed in accordance with NFPA 70E, Standard for Electrical Safety in the Workplace. c) General requirements for installing electrical products and systems are described in NECA 1, Standard Practices for Good Workmanship in Electrical Construction (ANSI). Other National Electrical Installation Standards provide additional guidance for installing particular types of electrical products and systems. A complete list of NEIS is provided in Annex A.

1



2. Switchboard Receiving, Handling, and Storing 2.1

Receiving the Switchboard

a) Unload carefully, observing all packing label warnings. b) Use forklifts or other loading equipment only for palletized shipments. c) Leaving protective coverings in place as much as possible, open and inspect the switchboard completely for shipping damage. Undamaged material should be carefully repacked unless intended for immediate installation. NOTE: Depending on company policy or project circumstances, it may be necessary to receive, unpack, and check all material at the company shop or other staging area, in which case, careful repacking is essential.

2.2

Handling the Switchboard

Switchboards are typically large, bulky pieces of equipment weighing several hundred pounds or more. The packing provides the actual weight of each item. Handle the switchboard properly to avoid injury to personnel and damage to equipment. Prior to receiving the shipment, verify the type of truck making the delivery and that the lifting capacity of the handling equipment is more than the shipping weight. Delivery on an open truck at the job site is recommended. Suitable protection against the weather must be provided if the equipment is designed only for indoor installation (NEMA Type 1).

2.2.1 Handling with lifting straps Switchboard manufacturers provide lifting straps as standard equipment when the weight of the switchboard section(s) does not exceed the recommended capacity of the lifting straps. Use a rigid spreader or a spanner beam to provide vertical lift on the lifting straps (see Figure 1), and avoid damage to the frame or finish. Follow lifting warning labels on the switchboard.

2.2.2 Handling without lifting straps Lifting straps are not furnished on switchboards when the weight of the section(s) exceeds their capacity, or when the lifting straps would cause stress to the switchboards. They also are not provided when the design does not permit, such as NEMA Type 3R outdoor equipment with overhangs. These switchboards can be handled by either slings, forklifts, rollers, or a combination of these means. Typically, a handling warning is provided on those switchboard sections for which lifting straps are not provided. a) Sling: A crane or suitably rigged equipment with a chain arranged in a sling, or wire cable with safety hooks and shackles, should be used to lift a switchboard shipping section not equipped with lifting

Spreader Beam Lifting Straps

There are two primary ways of lifting the equipment: with lifting straps and without lifting straps, using a sling instead. Using the manufacturer’s lifting straps is the preferable method when these are supplied. 

2

45° minimum angle

Figure 1: Handling switchboards with lifting st raps


straps. Rig the sling completely around the switchboard and shipping stringers (see Figure 2), and use a forklift or jacks to lift the switchboard vertically off the floor to attach the sling. b) Forklifts: Forklifts are an alternate method for handling switchboards. Verify that the capacity of the forklift is more than the weight of the load to be lifted. Always ensure that the form lengths extend under the entire switchboard and extend beyond the opposite side (see Figure 3). c) Rollers: If equipment is not available for lifting the switchboard, or the ceiling is not high enough, rollers suitable for the application may be used to move the switchboard into position. A forklift or jacks can be used to initially lift the switchboard and position it on the rollers. Rollers should be positioned approximately every 18 inches (457 mm), and

1/2 A or more A

45° min. angle

Do not pass ropes or cables through lift holes. Use slings with safety hooks or shackles.

NECA 400

be at least the width of the switchboard for stability. Extreme care should be taken when using rollers due to switchboard height and weight. Rollers are most suitable for moving switchboards on a level surface; use a winch or chainfall to prevent “runaway” where inclines must be traveled.

2.3

Storing the Switchboard

a) Cover the switchboard with a tarp or plastic to keep the equipment from getting wet and accumulating dust or debris (cement dust can be corrosive and cause insulation breakdown when it accumulates across insulators). The cover should be heavy enough to keep from tearing during wind gusts at the storage location. b) To reduce condensation within the switchboard enclosure, store the switchboard indoors whenever possible. c) Install a minimum of 250 watts of heat per vertical section, even for outdoor enclosures. Remove all loose packing or materials that could catch fire prior to applying the heat.

Spanner Bar (channel)

Switchboard (front or rear)

Blocks

Stringer 4x6 in 102x152 mm

Figure 2: Handling switchboards without lifting straps

SECURE MOTOR CONTROL CENTER TO FORKLIFT WITH SAFETY STRAP HERE.

FORKS UNDER ENTIRE MOTOR CONTROL CENTER

Figure 3: Handling switchboards with forklift

3



3. Installation

Proper installation is essential to the proper operation of all switchboard components. Thoroughly study associated instruction manuals, literature, and drawings before attempting to install the switchboard. In most cases, this information will already have been requested prior to the shipment of the switchboard to enable advanced planning.

3.1

Location

a) The floor plan of the structure for an inside switchboard, or the site plan for an outdoor switchboard will show the area where the switchboard is to be installed. The location of the switchboard should comply with all building codes, and at a minimum, should meet the working space requirements of the NEC 110.26. NOTE: Provisions for temporary ramps or installation hoists may require working clearances greater than NEC minimums. b) Consult the switchboard drawings to determine where accessibility is required for the switchboard (e.g., a rear access switchboard cannot be placed against a wall). c) Indoor switchboards in damp locations require shielding to prevent moisture and water from entering and accumulating. If the room temperature around the indoor switchboard is not between 77° – 104°F (25° – 40°C), use a minimum of 250 watts of heating per vertical section until the suitable environment can be provided. d) In locations where a sump pump is required, the pump should be properly working before the switchboard is installed to prevent accumulation of water that may seriously damage the switchboard and its internal components (see Section 7, Adverse 

4

Circumstances ). The sump pump should be connected to a standby power source.

3.2

Foundation Preparation

a) The floor or foundation on which the switchboard will be installed needs to be strong enough to support the weight of the switchboard without bowing or sagging. A concrete surface is preferred. b) In special instances where earthquakes may occur, 4000 psi concrete should be used along with specific anchoring means, such as stud anchors, sleeves anchors, or concrete anchor bolts (anchoring hardware is not supplied as a standard item with most switchboards). Performance of the switchboard under earthquake conditions is directly related to the foundation preparation. NOTE: Local building codes may have seismic requirements that affect switchboard installation. Installers should consult these codes or coordinate with the general contractor prior to installing switchboards. c) A level mounting pad raised four inches (100 mm) above the general floor level is typical with the surrounding floor area gently sloping toward a drain. To ensure correct bus bar alignment within the switchboard, and to enable bolting vertical sections together, it is critical that the mounting pad or floor be smooth and level. NOTE: Provisions for temporary ramps or installation hoists may require working clearances greater than NEC minimums. d) If floor channels are embedded in the concrete pad, they should be level over the entire length of the switchboard in order to avoid distortion of the switchboard structure.


e) Before pouring the concrete for the pad, install all conduits including future conduits required for bottom entry into the switchboard. Consult the bottom view switchboard drawing during this process to verify that the conduit layout matches the available conduit entry area into the switchboard. The manufacturer will already have taken into account the NEC and product listing requirements for conduit entry. f) Embedded conduits typically project above the finished pad approximately 2 inches (50.8 mm). If embedded conduits project more than 2 inches (50.8 mm) above the concrete pad, it may be necessary to lift each shipping section vertically into place using a crane, timbers, jacks, or forklift. After the sections are installed, and approximate extension sleeves added to the conduits, the maximum projection should be 3 inches (76 mm); NEC Section 408.5 prohibits projections greater than 3 inches (76 mm).

3.3

General Installation Instructions

a) Clean dirt and debris from the pad and surrounding area where the switchboard will be located before moving the switchboard into its final position. b) Remove the shipping skids before installing the switchboard on the pad. c) If the switchboard is equipped with bottom closure plates, temporarily remove these plates and set them aside. Cut holes for the conduits entering the bottom of each enclosure in the bottom plates (if supplied). Once the vertical sections have been installed, reinstall the bottom closure plates. d) Block the opening of each conduit with material that rodents will not be able to gnaw through, squeeze through, or push out of the way. Bottom closure plates will not keep out rodents that come in through the conduits.

3.4

Installing Vertical Sections

3.4.1 Initial placement a) If the switchboard has incoming cables or busway near or in its center, start with that vertical section first and work outward on each side.

NECA 400

b) If the switchboard is left-feed, start from the left. If right-feed, start from the right. c) If the switchboard is close-coupled to a transformer, start at the transformer and work away from the transformer.

3.4.2 Positioning Position each shipping section carefully, following the instructions in 2.2, Handling the Switchboard. Level with shims if necessary, and align each section with the previous section. Proper alignment will make joining the structures and through-bus easier. NOTE: Improper alignment of the through-bus may result in property loss, death, or serious injury.

3.4.3 Lifting straps Remove lifting straps or slings so that vertical sections can be joined flush. Leave lifting straps or hardware on the switchboard if their removal is not required to join adjacent sections flush together.

3.5

Joining Switchboard Sections

a) Open or remove the front, and, if necessary, the rear door or panels that provide access for bolting adjacent shipping sections together. b) Torque the bolts based on the manufacturer’s instructions. NOTE: The authority having jurisdiction (AHJ) may require that all bolts connecting bus sections be inspected for proper torque prior to closing up the switchboard.

3.6

Anchoring the Switchboard

Switchboard sections are freestanding structures, but hard bumps or shifting movements can result in damage to interior components, conduit hubs, and cable/busway connections. Therefore, each vertical section of the switchboard is anchored to the floor. Some manufacturers provide formed base channels that run the entire length of the switchboard, mounting holes in the structure base, or both (see Figure 4).

5



NECA 400


Anchor each section using the hardware recommended (but not usually supplied by) the switchboard manufacturer and torque the bolts to their recommended value.

3.6.1 Seismic considerations Carefully follow the plans and specifications when anchoring a switchboard for seismic conditions since the top of the switchboard structure can move as much as 3 inches (76 mm) in any direction. NOTE: Local building codes may have seismic requirements that affect switchboard installation. Installers should consult these codes or coordinate with the general contractor prior to installing switchboards.

3.7

Installing Cables

3.8.1 Through-bus splice connections Through-bus splice connections are extremely important to the performance of the switchboard, since these connections are expected to carry the full current intended for their operation. Failure to properly make through-bus splice connections may result in property damage, death, or serious injury. a) Through-bus splice kits are provided by the switchboard manufacturer when more than one section is required to be electrically connected together by through-bus. b) Splice kits may come in separate boxes, be installed on the through-bus of one or more vertical sections, or be stored inside the sections to be spliced.

Install the incoming services conductors and loadside cables after all switchboard sections are properly joined together and the entire switchboard structure is anchored to the floor. If the switchboard is in a seismic environment and cables or busway enter at the top of the switchboard, it is necessary to take into account the motion of the top of the switchboard during a seismic occurrence.

c) Follow the proper sequence of hardware installation, as specified in the manufacturer’s installation instructions. Install conical washers such that their convex or “top” side is against the nut (see Figure 5).

NOTE: If the switchboard consists of only one shipping section, proceed to Section 3.10.

e) The through-bus of some switchboards is covered with an insulating material. Follow the manufacturer’s instructions for installing insulation on each through-bus splice connection.

3.8 Installing Interconnections Between Switchboard Sections Switchboard vertical sections are electrically connected together using either through-bus or cables.

d) Torque the splice bolts to their recommended values. Mark each torqued connection with a permanent marker.

3.8.2 Cable Interconnections Install the interconnection cables (which may or may not be supplied by the manufacturer) between sections as shown on the manufacturer’s drawings. Hex Nut

1.13 in (29 mm)

Diameter hole in each corner for anchoring.

Washer— Marked “Top”

Switchboard Frame Secure the switchboard to the mounting surface using the holes closest to the surface. Formed Base Channel Mounting Surface

Figure 4: Anchoring the switchboard 

6

Bolt Head

Washer— Marked “Top”

Figure 5: Proper positioning of conical washers


Torque all connections to the manufacturer’s recommended values.

3.9

Ground Bus Splice Connections

Ground bus splice kits are provided by the switchboard manufacturers when more than one section is required to be electrically connected (see Figure 6). Proper installation of ground bus splice connections is essential to providing a low-impedance path to ground for temporary current resulting from phaseto-ground faults. a) Splice kits may come in separate boxes, be installed on the ground bus of one or more sections, or be stored inside the switchboard sections. b) Follow the proper sequence of hardware installation, as specified in the manufacturer’s installation instructions. Install conical washers such that their convex side is against the nut. c) Torque the splice bolts to the recommended value. Mark each torqued connection with a permanent marker.

3.10

Grounding and Bonding

3.10.1 Ground systems – service-entrance switchboards and switchboards used on separately derived systems NEC 250.64 describes complete grounding requirements for grounded separately derived systems.

Figure 6: Ground bus splice connections

NECA 400

a) Run a grounding electrode conductor from the grounding electrode at the installation site to the grounding electrode conductor connection, commonly called a ground lug, located on the switchboard ground bus (see Figure 7). b) NEC 250.67 describes requirements for grounding electrode conductor material, installation, and size. c) Torque the ground lug binding screw based on the manufacturer’s recommendation or crimp in accordance with the crimp tool’s instructions. d) For service entrance equipment, or a switchboard used on a separately derived system, install the system bonding jumper between the neutral bus and the ground bus. A label on the front of the switchboard will identify the section(s) that incorporate the system bonding jumper(s). e) Torque the hardware of the main bonding jumper in accordance with the manufacturer’s recommendations. f) Equipment ground-fault protection will be rendered inoperative if the system is grounded downstream from the ground fault sensor. g) For switchboards with multiple sources of power, there will be two or more main bonding jumpers to install.

Figure 7: Ground lug

7



NECA 400


3.10.2 Ungrounded systems – service-entrance switchboards and switchboards used on separately derived systems. NEC 250.64 describes complete grounding requirements for ungrounded separately derived systems. a) Run a grounding electrode conductor from the ground electrode at the installation site to the grounding electrode conductor connection, commonly called the ground lug, located on the switchboard ground bus (see Figure 7). b) NEC 250.66 describes requirements for grounding electrode conductor material, installation, and size. c) Torque the ground lug binding screw based on the manufacturer’s recommendation or crimp per the crimp tool’s instruction.

3.11 Busway Connections Power is often distributed from switchboards using busway, also called bus duct. Busway is provided in different configurations by different manufacturers; one typical configuration is shown in Figure 8. a) When connecting busway, install conical washers so the convex side of the washer is against the nut.

b) Confirm proper phasing of the busway before energizing the busway run. c) Do not use the switchboard to support the weight of the busway. Support the busway independently of the switchboard.

3.12

Conduit Area

a) The switchboard conduit entry drawings show the available conduit entry for the switchboard. External circuit cables for each section should be routed into and through these designated conduit areas, then routed internally to their designed termination areas. b) Do not use the switchboard to support the weight of the conduits. Support the conduits independently of the switchboard. c) If a bottom plate is furnished, remove it to cut holes for the conduit and cable entry. Bottom plates with holes are not furnished as a standard item. Reinstall the bottom plates after the holes are made. Saw kerf between conduit holes in bottom plate for installations where conduits, such as duct bank risers, carry phase conductors from only one phase (isolated phase arrangement) to prevent a magnetic loop from causing overheating within the switchboard. d) Under seismic conditions, the top of the switchboard may move up to 3 inches (76 mm) in any direction. Any cables entering the top of the switchboard need sufficient slack to accommodate this motion. If the floor of the switchboard is designed for movement during a seismic event, the cables entering the bottom of the switchboard should also have enough slack to accommodate this motion. e) Use approved hubs and ring connectors to protect the cables and prevent condensation from entering the switchboard through the conduits. f) Bond all conduits, stubs, and ring connectors to the switchboard enclosure following the manufacturer’s recommendations.

Figure 8: Busway connector (bus duct) 

8


3.13

Cable Pulling

Switchboard components are arranged to provide clearance and wire bending space for both line and load cables. Each cable should be pulled into the switchboard to conform to the arrangement specified on the switchboard drawings. a) Verify that the lugs correspond to the switchboard cable schedule and are suitable for the cables being terminated. Consult the markings on overcurrent protective devices to determine that the conductor size range is correct and the temperature rating is appropriate. Conductors rated 194°F (90°C) are permitted to be used with most connectors and terminals, but only at 167°F (75°C) ampacity. Some overcurrent protective devices, mostly those listed for operation at 100 percent of rated ampacity, require the use of 194°F (90°C) conductors sized at 167°F (75°C) ampacity. b) Consult NEC Article 310 to calculate the proper size and number of conductors for the loads served. c) Prior to pulling the cables into the switchboard, plan ahead as to which overcurrent device to cable first. This is particularly important for groupmounted constructions. d) Cable pulling lubricants should not be allowed to drip or come into contact with overcurrent devices and/or plating of the bus bars. Remove all pulling compound from the interior of the switchboard prior to energizing the unit. e) Position the conductors in the switchboard enclosure so they are not subject to physical damage. If any conductors are in contact with structural members, place suitable protective material at the contact point to protect the cable insulation. f) NEC 300.20(A) requires that all phase and grounded conductors of the same circuit pass through the same metal opening together. Otherwise, a magnetic loop will be created causing overheating within the switchboard.

NECA 400

g) Where required, brace or lace the conductors in accordance with the manufacturer’s instructions or consulting engineer’s specifications. h) Train cables within wire gutters of switchboards in a neat and workmanlike manner.

3.14 Cable Terminations Terminating and tightening cable connections to the manufacturer’s recommended torque value is imperative to a satisfactory connection. Follow these steps when terminating conductors at the switchboard: a) Strip a sufficient length of insulation from the cable end to fit into the full length of the lugs barrel. Use a proper insulation stripping tool to avoid nicking conductor strands. Stripping cable too long should be avoided since the through-air clearance could be reduced below the minimums required by the NEC. b) Mechanical lugs (set-screw type) are the most common type of connector furnished with switchboards. Torque these lugs in accordance with the manufacturer’s recommendations to avoid stripping threads or cracking the lug body. c) When compression lugs are used to terminate aluminum conductors, remove oxides from the conductors and apply an antioxidant compound to the aluminum conductor before inserting into the lug body. Oxides on aluminum conductors are poor conductors and will cause abnormal heating at the connection. d) Remove compression lugs from their point of termination in order to crimp them onto cables. Follow the manufacturer’s recommendation as to the proper number of crimps and their position on the lug. Use the recommended sealant. Reinstall the crimp lugs to the lug pad and torque the hardware used with the lugs.

9



4. Pre-Energizing Checkout Procedure 4.1

General

Conduct a complete inspection of the switchboard before it is energized to ensure that the components within the switchboard function properly. a) Check all field-installed bus bar connections for correct torque value. b) Check all accessible connections for tightness.

4.3

Current Transformers

Ensure that current transformers’ secondary terminals are connected to a load or are shorted together using shorting straps or terminal block shorting screws. CAUTION: Open secondary terminals may have high voltages, which could be a hazard to people or equipment.

c) Check all factory and field-installed lug terminations for the correct torque value.

The shortening means are removed when the current transformers operate normally with their intended load.

d) Visually check the bussing insulators for cracks and supports for damage.

4.4

e) Check to ensure that dents or other damage to the enclosure have not resulted in clearances that violate NEC requirements. f) Remove foam blocks, packing material, and temporary cushioning from the switchboard and components inside the switchboard. g) Check all relays, meters and instrumentation device wiring, and terminations.

4.2

Insulation Test

Perform a direct current (DC) insulation test on the switchboard and record the value for future maintenance tests; a switchboard insulation resistance chart is shown in Section 9. Values less than 1 megohm are typically unacceptable. Prior to this test, remove control power fuses and any other equipment that should not be subjected to this level of potential.



10

Circuit Breakers and Fusible Switches

a) Manually open and close all circuit breakers and fusible switches to ensure proper operation. b) Adjust the magnetic trip on thermal magnetic circuit breakers to their proper setting based on the system study or switchboard schedule. A setting too low for a load that has a high peak inrush current will trip the circuit breaker on start-up. c) Electronic circuit breakers have functions such as long-time, instantaneous, short-time, and groundfault, which require initial adjustment. Settings typically are provided in a coordination study prepared by the consulting engineer or other persons responsible for the switchboard set-up. NOTE: These values typically are not found on the drawings supplied by the switchboard manufacturer. If values are not provided, consult the manufacturer’s circuit breaker instruction manual for values that will set the electronic circuit breaker functions to emulate thermal magnetic circuit breaker characteristics.


4.5

NECA 400

Ground-fault Protection

a) The trip and time-delay on ground-fault protective equipment are typically set by the manufacturer at their lowest settings. Adjust these settings based on information provided in a coordination study prepared by the consulting engineer or other persons responsible for the switchboard set-up. b) Some ground-fault protection systems require field connections at the job site. Consult the switchboard interconnection wiring diagram for details. c) Check the ground-fault circuitry and establish that there are no grounds on the neutral downstream from the service entrance point. d) The NEC requires that the ground-fault protection system be performance tested when first installed, and that a written record of this test be available to the AHJ. A testing group with experience in switchboard ground-fault testing should perform an injection test.

4.6

Interconnections

Verify that all interconnecting wiring between switchboard sections has been connected.

4.7 Power Fuses and Control Power Disconnects Replace all control power fuses removed in the Insulation Test (see Section 4.2) and turn on all control power disconnects.

4.8

Clean-up

Vacuum all scrap, wire, dust, and other debris from the switchboard. Do not use compressed air to blow debris out of the switchboard, since debris may instead settle inside devices and impair their ability to function.

4.9

Close-up

Replace all covers. Check for any pinched wires and close all doors. Make sure that the enclosure parts are properly aligned and fastened securely.

11



5. Energizing the Switchboard

WARNING: Arc flash, arc blast, and shock hazards exist when energizing switchboards. Switchboards should only be energized by qualified persons, following work practices defined in NFPA 70E. If a short circuit or ground-fault condition, caused by damage or poor installation practices exists, and this is not detected and corrected during the checkout procedures, serious personal injury and/or damage to the switchboard can result when the switchboard is first energized. Follow the steps below to energize the switchboards; read all steps before proceeding. Step 1 Turn off all downstream loads. No load should be on the switchboard when it is first energized.



12

Step 2 Use remote operators, if available, to close devices and energize switchboards and loads for the first time. Step 3 Prior to energizing any circuit that supplies rotating machinery, verify that the phase sequence is correct. Serious damage can result to motors and similar equipment rotating in the wrong direction. Step 4 One by one, close each circuit breaker or fusible switch in the switchboard. Step 5 Proceed to energize (turn on) the downstream loads (lighting circuits, contactors, heaters, motors, etc.) one at a time.

6. Switchboard Maintenance

Periodic maintenance of switchboards extends service life and increases reliability. Cleaning, inspection, maintenance, and testing should only be performed by qualified personnel on switchboards to which power has been turned-off, disconnected, and electrically isolated, unless required for testing, so that no accidental contact can be made with energized parts. Follow all manufacturer’s warnings and instructions. The interval between maintenance checks varies depending on the environment, such as ambient temperature and conditions in the switchboard room, and usage of the equipment. For switchboards energized and in service, perform periodic routine inspections, such as making limited visual observations and recording operational data. Perform cleaning, inspections, maintenance, and testing of switchboards at least annually, but as often as the operating environment requires keeping switchboards clean. Perform the first inspection and maintenance no more than one year after the original installation. Plan cleaning, inspections, maintenance, and testing to minimize outages. In accordance with manufacturer recommendations, clean, inspect, maintain, and test switchboards following any unusual operating condition, such as whenever an overcurrent protective device opens, or a phase-to-phase short circuit or ground-fault occurs (see Section 7.1).

6.1

Routine Inspections

Inspect areas and spaces around switchboards for any accumulation of dirt or dust. Remove any accumulations of dirt or dust. Remove trash, combustible material, and other debris from areas around switch-

boards. Use the rate of accumulation of dust and moisture on visible surfaces as a guide for scheduling cleaning, inspections, maintenance, and testing. Inspect switchboards for external signs of overheating. Measure and record the ambient temperature. Check equipment installed near switchboards that might be an external source of heat. Eliminate external sources of heat to switchboards. Check the operating temperature of switchboards that have been operating under normal load and at normal ambient temperature for a minimum of 3 hours by measuring the surface temperature of switchboard access covers, doors, circuit breakers, and switches. If the temperature exceeds manufacturer recommendations, deenergize switchboard and investigate sources of overheating. Record switchboard voltage and load currents, if equipped with meters, noting the date and time of day. Provide comments regarding known causes of variations in loading, such as load additions or equipment maintenance outages. Check all accessible exterior switchboard hardware for tightness. Visually inspect enclosures for physical damage. Repair physical damage, if practical, and as approved by the manufacturer. Consult owner and switchboard manufacturer for recommendations for suitable protective barriers to prevent future damage. Inspect areas and spaces around switchboards for evidence of water or moisture. Eliminate sources of water or moisture, or provide switchboards suitable protection from sources of water.

13



NECA 400

6.2


Safety Procedures

Before cleaning, inspecting, testing, or maintaining, de-energize and electrically isolate equipment in accordance with established procedures. Consider all circuits live until they are confirmed to be de-energized by testing and are locked out of operation. Do not work on energized equipment. Guard energized conductors and equipment in close proximity to work. Failure to observe these precautions may result in severe personal injury or death. Personnel working on or near energized switchboards should follow the safe work practices described in NFPA 70E, including the use of personal protective equipment (PPE) appropriate for the task being performed. Apply lockout/tagout procedures in accordance with documented and established policies and practices. Render electrical circuit conductors and circuit parts electrically safe by removing all sources of energy by opening all upstream source disconnecting means, locking and tagging out all source disconnecting means, verifying the absence of voltage using an approved voltage testing device, and guarding any exposed energized components. Remove the front cover of the switchboard and attach grounding leads to the line terminals of the main circuit breaker or main lugs, to the neutral terminal bus bar, if so equipped, and to the grounding terminal.

6.3

Cleaning and Inspections

Consult manufacturer recommendations for cleaning and inspecting switchboards and components. Deenergize switchboards in accordance with Section 6.2 prior to performing any cleaning or inspections. Visually inspect switchboards for evidence of discoloration, abnormal dust accumulation, metal shards, or any other indication of overheating, wear, or other abnormal conditions prior to cleaning. Visually inspect the switchboard for signs of overheating. Discoloration and flaking of insulation or metal parts are indications of possible overheating. Correct 

14

conditions that cause the overheating, and replace the affected parts before re-energizing the switchboard. Vacuum the inside of switchboards to remove any debris, dirt, or dust that has accumulated, noting anything unusual, such as signs of insects, rodent activity, or moisture. Avoid blowing dust into switchboards. Do not use a blower or compressed air. Maintain adequate ventilation during cleaning. Wipe bus bars, insulators, conductors and other parts with a clean, dry lint-free cloth. Do not use chemicals or petroleum-based solvents that may degrade plastics or insulating materials. Visually inspect the inside of the switchboard for moisture, condensation build-up, or signs of any previous wetness. Moisture causes insulation failures and rapid oxidation of current-carrying parts. Pay particular attention to conduit entrances and the top of the switchboard between sections. Remove any moisture present inside the switchboard and seal off all leaks. Replace any components that show evidence of damage from moisture. Carefully inspect all switchboard devices for any worn-out, cracked, or missing parts. Inspect terminations, connections, and lugs for alignment, physical damage, burns, corrosion, discoloration, flaking, heat damage, arcing, pitting, melting, deterioration, carbonization, cracks, chips, breaks, partial discharge, or moisture. Replace damaged components. Investigate and eliminate sources of damage. Plated parts may become dark over a period of time due to oxidation. Removing this discoloration will reduce the thickness of the plating. Consult the manufacturer for recommendations regarding discoloration of parts. Verify that all key interlocks and door interlocking provisions are working properly.

6.4

Maintenance and Testing

Consult manufacturer recommendations for maintaining and testing switchboards and components. De-energize switchboards in accordance with Section 6.2 prior to performing any maintenance or testing.


6.4.1 Infrared Scan After cleaning and inspecting switchboards and components in accordance with Section 6.3, perform an infrared scan in accordance with switchboard and test equipment manufacturer recommendations. With the switchboard de-energized, remove accessible covers, plates, weathershields, etc. Provide supplemental barriers and safety precautions during infrared scan to prevent accidental contact with exposed energized components. Personnel working on or near energized switchboards should follow the safe work practices described in NFPA 70E, including the use of personal protective equipment (PPE) appropriate for the task being performed. Energize the switchboard in accordance with Section 6.6, and turn on all normal loads supplied by the switchboard. Perform an infrared scan of all switchboard electrical connections and terminals while energized and operating under normal load conditions. Use an infrared scanning device designed to measure actual operating temperatures or designed to detect significant deviations from surrounding conditions. Provide documentation of device calibration. Prepare a certified report identifying the switchboard tested and describing the results of the infrared scan. Include notations of deficiencies detected, remedial actions taken, and results from retesting after remedial actions. Consult switchboard manufacturer for repair or replacement recommendations if infrared scan results indicate overheating of components. De-energize the switchboard in accordance with Section 6.2.

6.4.2 Bus Bar Joints Consult the manufacturer’s recommendations concerning bus bar joints, and retorque where required. Some switchboard bus bar joints are maintenancefree. Additional tightening after installation may degrade these connections.

NECA 400

Replace parts that show indications of pitting, corrosion, discoloration, or annealing due to overheating. Do not use abrasive materials on bus bar joints. Use hardware and washers of a grade identical to or better than the hardware replaced.

6.4.3 Molded-Case Circuit Breakers a) Clean circuit breaker surfaces. Remove dust, soot, grease, moisture, and foreign material. b) Operate circuit breakers several times to exercise the mechanism and contacts, and to ensure smooth operation. Many circuit breakers have a test feature which trips, exercises, and lubricates the mechanism. This method of exercising circuit breakers should be used if available. If unavailable, operate circuit breakers manually. Do not oil or grease parts of molded case circuit breakers. Replace circuit breakers that do not operate smoothly. c) Check circuit breakers for visual defects, chips, cracks, breaks, burns, and deterioration. Visually check circuit breakers for evidence of overheating and thermal damage. Investigate and eliminate sources of overheating. Replace damaged circuit breakers. d) For circuit breakers that use solid-state circuitry or a microprocessor, run the self-diagnostic program, if available. For electronic circuit breakers, use the test set to run trip unit test automatically with user prompts. Repair or replace circuit breakers in accordance with manufacturer recommendations.

6.4.4 Bolted Pressure Switches Exercise bolted pressure switch operating mechanisms. Check the cover interlock with the switch in the “on” position. The cover should not open using normal hand force. Lubricate parts using materials and methods in accordance with manufacturer recommendations.

6.4.5 Fusible Switches a) Thoroughly clean fusible switches inside and outside. Clean contact areas of fuses and fuse holders.

15



NECA 400


Wipe insulating areas of fuses with a clean, dry, lintfree cloth. b) Operate each switch several times to ensure that all mechanisms are free and in proper working order. Check switches for damaged or broken parts, free movement, corrosion, dirt, and excessive wear. Verify proper blade penetration, travel stops, and mechanical operation. Repair or replace switches in accordance with manufacturer recommendations. c) Inspect contact surfaces, blades, and jaws for discoloration, overheating, pitting, arcing, and corona. Inspect arc chutes. Clean and dress readily-accessible copper electrical contacts, blades, and jaws in accordance with manufacturer recommendations. Repair or replace burned contacts. Many contact surfaces, such as arcing contacts, are silver tungsten or other types of materials that must never be dressed. When contacts of these materials require maintenance, they must be replaced. If contact clips have lost their tension, replace clips or replace the switch. Consult the manufacturer for recommendations. d) Tighten fuse holder connections in accordance with manufacturer recommendations. Inspect each fuse holder to determine whether it seems to be adequately supporting the fuse and that the fuse holder is securely attached to the mounting base. Inspect fuse clips for discoloration, overheating, corrosion, or physical damage. Replace weak or burned clips. Install new fuse clips and suitable clamps. Use manufacturers’ replacement parts. e) Lubricate operating mechanisms and sliding contact surfaces, if required, according to manufacturer’s instructions. If no instructions are given on the devices, sliding copper contacts, operating mechanisms, and interlocks may be lubricated with clean, light grease. Wipe off excess lubrication to avoid contamination. f) Check the cover interlock with the switch in the “on” position. The cover should not open using normal hand force. Inspect switches for any damaged or broken parts. Check the fuse mounting clips or bolted contact area for corrosion or discoloration due to overheating. Replace damaged or broken parts as necessary. 

16

6.4.6 Inspecting and Replacing Fuses Ensure that equipment is de-energized before inspecting and replacing fuses. Test line and load terminals of switches for the presence of voltage before replacing fuses. Turn the switches to the “off ” position before opening the door. Do not defeat cover interlocks to gain access to fuses. Visually inspect switch blades to verify that all blades are disconnected from the line connections. Consult the manufacturer for recommendations when blades do not disconnect from line connections. a) Check all fuses to ensure that the correct type and rating are installed. Where renewable fuses are used, examine fuse links to ensure that the correct link is installed. NOTE: Some switchboard manufacturers do not recommend the use of renewable link fuses in their equipment. b) Look for fuses that have been bridged with wire, metal strips, disks, or appear to have been forced or hammered in, etc. Replace with correct fuses and consult the manufacturer for recommendations for preventing a recurrence. c) Look for evidence of overheating of cartridge fuses. Replace fuses having discolored or weakened casings. Investigate the cause of overheating. d) Inspect ferruled or knife blades of cartridge fuses for corrosion or oxidation. Clean and polish contact surfaces. Clean surfaces with a noncorrosive cleaning agent. Plated parts may become dark over a period of time due to oxidation. Removing this discoloration will reduce the thickness of the plating. Consult the manufacturer for recommendations regarding discoloration of parts. e) Measure fuse resistance. Investigate fuse-resistance values that deviate from each other by more than 15 percent. Replace defective or partiallyburned fuses. Retighten plug fuses. f) Replace fuses with fuses of like types and ratings. Ensure that non-current-limiting devices are not


used as replacements for current-limiting devices. Do not defeat any rejection feature in any switchboard fusible device.

6.4.7 Ground-Fault Protection Systems a) Check the torque of terminal connections on ground-fault protection systems annually. Inspect for corrosion and for physical, thermal, and electrical damage. Replace any damaged components. b) Test the ground-fault protection system in accordance with manufacturer recommendations. Testing may be conducted with or without tripping main or branch overcurrent protective devices. Testing with trip is preferable since it ensures the whole system is functioning. Energize the switchboard in accordance with Section 6.6 prior to testing. c) If the ground-fault protection system does not operate properly and additional equipment has been connected to the installation since the last maintenance test/check, de-energize the entire system in accordance with Section 6.2, disconnect the main bonding jumper, and check for continuity between the neutral and ground on the load-side of the main bonding jumper. If grounds are found, remove them and test again. If no grounds are detected, and the ground-fault protection system is still not functioning properly, consult the switchboard manufacturer for recommendations. d) If the ground-fault protection system does not operate properly, and no additional equipment has been connected to the installation since the last maintenance test/check, check the devices for physical or electrical damage and replace accordingly. Check wiring for damage or loose connections and correct any problems found. Consult the switchboard manufacturer for recommendations.

6.5

Insulation Resistance Test

Perform an insulation resistance test on switchboards using a 1000 VDC megohmmeter. Disconnect all accessories and electronic devices that may be sub jected to the test voltage. Test from phase-to-ground and from phase-to-phase with all switches and circuit breakers in both the open and closed positions, all

NECA 400

instrumentation and control fuses removed, and no loads connected to the switchboard. Ground all phases not being tested. Connect megohmmeter between each phase and ground, and between each phase. Measure insulation resistance at one minute intervals following the application of the test voltage. Record the megohm values of each phase and between each phase, along with the description of the instrument, voltage level, humidity, temperature, time, and date of the test. Consult switchboard manufacturer's published data for acceptable test results. If published data is not available, investigate any values that deviate from previous test results under similar conditions by more than 50 percent of the lowest value. Investigate any results less than 1 megohm with the overcurrent protective devices in the open position for possible tracking on insulation or insulation breakdown. Ground each phase at the completion of the test. Maintain records of testing for future reference.

6.6

Re-energizing Switchboards

Energize switchboards in accordance with Section 5. Remove grounding leads from the line terminals of the switchboard. Visually inspect the system to ensure that all tools, electrical jumpers, test devices, etc., have been removed. Visually inspect equipment and areas around equipment to ensure that all persons are clear from circuits and equipment to be reenergized. Remove locks and tags only after work is complete and tested, and all personnel are clear of the area. Test for short circuits or ground-faults. Energize circuits using established switching procedures. Close disconnect means starting at the source, working toward the load. Measure phase-to-phase and phaseto-neutral voltages, if applicable. Investigate source of voltage imbalance greater than 3 percent. Measure switchboard feeder and branch load currents. Verify that conductors are properly sized and protected for actual loading.

17



7. Adverse Circumstances

Special procedures are necessary to determine whether a switchboard can safely remain in service following a short circuit, ground-fault, or exposure to water.

7.1 Inspection Following a Short-Circuit or Ground-Fault Condition Do not attempt to re-energize a switchboard following a short-circuit or ground-fault condition within the switchboard. Do not re-energize a feeder or branch overcurrent protection device in the switchboard that has opened due to a short circuit or ground-fault until the problem downstream has been corrected. Following a short-circuit or ground-fault within a switchboard, inspect the equipment thoroughly as described in Section 6.1 to verify that damage has not occurred to conductors or insulators within the switchboard. NOTE: The insulating properties of some organic insulating materials may deteriorate during an electrical arc. Replacement of the damaged insulating material is the only remedy.

7.1.1 Short-circuits develop high mechanical stresses that can damage conductors and insulation Improper and loosened connections may result in conductors pulling out of their terminations on subsequent short-circuits. For this reason, all connections should be inspected and, if necessary, re-evaluated. Great care must be taken in evaluating the cause of the short circuit. Do not replace the fuse(s) and turn the overcurrent protective device back on, or reset the circuit breaker, without first determining whether it is safe to energize the circuit. Phase-to-phase short circuits that originate on bus bars can travel the length 

18

of the bussing system through the switchboard, and the greatest damage may not occur where the arcing condition originated. Conduct an insulation test to determine the integrity of the switchboard insulation prior to re-energizing the switchboard.

7.1.2 Ground-faults are unintentional current paths between a phase conductor and ground Depending on the magnitude of the ground-fault and its duration, carbon build-up and metallic splatter may need to be removed, insulators cleaned or replaced. Perform phase-to-phase and phase-toground insulation tests, with a minimum reading of one megohm, prior to turning the switchboard power back on.

7.2 Replacing a Switchboard Soaked by or Submerged in Water a) Do not work on energized electrical equipment when standing in water. b) Do not energize a switchboard that is wet. c) Do not clean or repair a switchboard that has been submerged in or exposed to large volumes of water. Current-carrying parts, insulation systems, and electrical/electronic components may be damaged beyond repair through contamination by chemicals, river or creek water, sewage, and other pollutants. In this event, replace the switchboard rather than attempt to repair it.

7.3 Inspecting and Re-Energizing a Switchboard Sprayed or Splashed with Clean Water Apply heat (a minimum of 250 watts per section) to the switchboard to dry it out until visible signs of


dampness cannot be seen. Remove materials that could catch fire prior to applying the heat. Consult the manufacturer’s recommendations for specific guidelines on how to ensure that it is safe to re-energize the switchboard, or follow this procedure.

7.3.1 Preliminary Inspection Follow the steps in Section 7.3.2 to re-energize the switchboard only if a preliminary inspection verifies that the following conditions are satisfied: a) There are no signs of physical damage to the equipment. b) The switchboard has not been soaked by or submerged in water. c) The water that has been in contact with the switchboard has not been contaminated with sewage, chemicals, or other substances. d) Water has not entered any area of the switchboard enclosure that contains wiring, and has not come into contact with any live part. Look for water entering through conduits. If all of the conditions listed above are satisfied, proceed as follows.

NECA 400

Voltage cannot be present on the switchboard during the insulation resistance test. Step 4 Use a DC insulation-resistance tester with a capacity of 500-1000 volts DC to perform phase-toground and phase-to-phase insulation tests. NOTE: Use of an AC dielectric tester is not recommended. a) Measure each phase-to-ground (A, B, C) with the circuit breakers or fusible switches “on”. b) Measure each phase to another phase with the circuit breakers or fusible switches “on”. Record the values of the insulation resistance on the insulation resistance chart shown in Section 9. Step 5 Do not re-energize the equipment if any of the resistance measurements are not at least 0.5 megohm. If moisture is the cause of the low resistance readings, the moisture can be removed from the switchboard by providing a minimum of 250 watts of heat per vertical section. Step 6 If the resistance measurements are greater than 0.5 megohom, the equipment can be re-energized.

7.3.2 Cleaning, testing, and re-energizing a switchboard Step 1 Completely de-energize and electrically isolate the switchboard so that contact cannot be made with energized parts. Step 2 Wipe off all moisture from bus bars, insulators, and insulating materials with a clean, dry, lintfree cloth. Never use cleaning agents or sprays unless specifically recommended by the switchboard manufacturer. Step 3 Prepare the switchboard for an insulation resistance test by disconnecting all line-side supply conductors and all load-side conductors to isolate the switchboard from the wiring system. Turn all circuit breakers or fusible switches to the “on” position.

19



8. Recommended Torque Values

If the switchboard manufacturer does not provide specific torque recommendations, use the following as a guide.

Hardware Description 1/2 inch

Hardware Description

Torque Value 780-900 lb-in (88-102 N*m)

Torque Value

1/4 inch

50-75 lb-in (6-8 N*m)

5/16 inch

80-125 lb-in (9-14 N*m)

3/8 inch

175-225 lb-in (20-25 N*m)

1/2 inch

250-350 lb-in (28-40 N*m)


Torque Value

3/8 inch

175-225 lb-in (20-25 N*m)

1/2 inch

250-350 lb-in (28-40 N*m)



20


3/8 inch

1/2 inch


5/16 inch 3/8 inch

Torque Value Conical Washer OD

Square Head (Tee) Bolt Conical Washer

0.87 inches (22 mm)

250-280 lb-in (28-32 N*m)

1 inch (25 mm)

130-150 lb-in (15-17 N*m)

1.25 inches (32 mm) 2.25 inches (57 mm)

450-550 lb-in (51-62 N*m)

Torque Value Conical Washer OD

Hex Head Bolt (2) Conical Washers

0.90 inches (23 mm)

145-260 lb-in (16-29 N*m)

0.87 inches (22 mm)

250-280 lb-in (28-32 N*m)

1 inch (25 mm)

130-150 lb-in (15-17 N*m)

1.25 inches (32 mm) 1/2 inch

2.25 inches (57 mm)

780-900 lb-in (88-102 N*m)

3.00 inches (75 mm)

21



9. Switchboard Insulation Resistance Chart NOTE: The use of a AC dielectric tester for testing the motor control center is not recommended. Use an insulation resistance tester with a capacity of 500-1000 V DC.

Phase-to-Phase

Phase-to-Ground

Date

All Disconnects Open A-B

B-C

C-A

Phase-to-Phase

Date

22

A-GND

B-GND

C-GND

Phase-to-Ground

N-GND

Neutral-to-Ground

All Disconnects Closed A-B



Neutral-to-Ground

B-C

C-A

A-GND

B-GND

C-GND

N-GND

10. Operations and Maintenance Documents This standard refers to manufacturers’ packing label warnings (2.1a), instruction manuals, literature, drawings (Section 3), recorded values of tests (4.2, 7.3.2, 9), and set values of adjustable trips (4.4 and

4.5a, 4.5d). This material, plus as-built drawings, should be assembled, identified, and delivered to the owner of the facility at the completion of the installation.

23



(This annex is not part of the standard)

Annex A: Reference Standards

This publication, when used in conjunction with the National Electrical Code and manufacturers’ literature, provides sufficient information to install and maintain switchboards. National Fire Protection Association 1 Batterymarch Park P.O. Box 9101 Quincy, MA 02269-9101 (617) 770-3000 tel (617) 770-3500 fax www.nfpa.org NFPA 70-2005, National Electrical Code (ANSI) NFPA 70E-2004, Standard for Electrical Safety in the Workplace Current National Electrical Installation Standards ™ Published by NECA: National Electrical Contractors Association 3 Bethesda Metro Center, Suite 1100 Bethesda, MD 20814 (301) 215-4504 tel, (301) 215-4500 fax www.neca-neis.org NECA 1-2006, Standard for Good Workmanship in Electrical Construction (ANSI) NECA 90-2004, Recommended Practice for Commissioning Building Electrical Systems (ANSI) NECA 100-2006, Symbols for Electrical Construction Drawings (ANSI) NECA 101-2006, Standard for Installing Steel Conduits (Rigid, IMC, EMT) ( ANSI) NECA 102-2004, Standard for Installing Aluminum Rigid Metal Conduit (ANSI) NECA/AA 104-2006, Recommended Practice for Installing Aluminum Building Wire and Cable (ANSI) NECA/NEMA 105-2002, Recommended Practice for Installing Metal Cable Tray Systems NECA 111-2003, Standard for Installing Nonmetallic Raceways (RNC, ENT, LFNC) (ANSI) NECA/NACMA 120-2006, Standard for Installing Armored Cable (AC) and Metal-Clad Cable (MC) (ANSI)



24


NECA 400

NECA 200-2002, Recommended Practice for Installing and Maintaining Temporary Electrical Power at Construction Sites (ANSI) NECA 202-2006, Standard for Installing and Maintaining Industrial Heat Tracing Systems (ANSI) NECA 230-2003, Standard for Selecting, Installing, and Maintaining Electric Motors and Motor Controllers (ANSI) NECA/FOA 301-2004, Standard for Installing and Testing Fiber Optic Cables (ANSI) NECA 303-2005, Standard for Installing Closed-Circuit Television (CCTV) Systems (ANSI) NECA 305-2001, Standard for Fire Alarm System Job Practices (ANSI) NECA 331-2004, Standard for Building and Service Entrance Grounding and Bonding NECA 400-2007, Standard for Installing and Maintaining Switchboards (ANSI) NECA 402-2007, Recommended Practice for Installing and Maintaining Motor Control Centers (ANSI) NECA/EGSA 404-2007, Standard for Installing Generator Sets (ANSI) NECA 406-2003, Standard for Installing Residential Generator Sets (ANSI) NECA 407-2002, Recommended Practice for Installing and Maintaining Panelboards (ANSI) NECA 408-2002, Recommended Practice for Installing and Maintaining Busways (ANSI) NECA 409-2002, Recommended Practice for Installing and Maintaining Dry-Type Transformers (ANSI) NECA 410-2005, Standard for Installing and Maintaining Liquid-Filled Transformers (ANSI) NECA 411-2006, Standard for Installing and Maintaining Uninterruptible Power Supplies (UPS) (ANSI) NECA 430-2006, Standard for Installing Medium-Voltage Metal-Clad Switchgear (ANSI) NECA/IESNA 500-2006, Standard for Installing Indoor Commercial Lighting Systems (ANSI) NECA/IESNA 501-2006, Standard for Installing Exterior Lighting Systems (ANSI) NECA/IESNA 502-2006, Standard for Installing Industrial Lighting Systems (ANSI) NECA 503-2005, Standard for Installing Fiber Optic Lighting Systems NECA/BICSI 568-2006, Standard for Installing Commercial Building Telecommunications Cabling (ANSI) NECA/MACSCB 600-2003, Recommended Practice for Installing and Maintaining Medium-Voltage Cable (ANSI) NECA/NEMA 605-2005, Recommended Practice for Installing Underground Nonmetallic Utility Duct (ANSI)

24



Switchboards

Recommend Documents