CONDUCTORS AND WIRING ACCESORIES by Engr . Alexis T. Belonio Department of Agricultural Engineering and Environmental Management College of Agriculture Central Philippine University Iloilo City
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Introduction
Electrical conductors are substance or materials used to convey or allow the flow of electric current
Silver, copper, aluminum, etc
Electrical insulators are substance or materials that resist the flow of electric current
Rubber, porcelain, etc
Introduction
Electrical conductors are substance or materials used to convey or allow the flow of electric current
Silver, copper, aluminum, etc
Electrical insulators are substance or materials that resist the flow of electric current
Rubber, porcelain, etc
Wires – they are smaller conductors 8 mm (AWG No. 8) and below Cables – they are larger than wire Cord – is an insulated stranded wire
Characteristics of Wire Size Wire Size AWG
Current Carrying Capacity 2 to 3 wires inc cable or raceway (Amp)
Area Circular Mills
Resistance Ω/1000 ft
Current Carrying Capacity Amp for Single Wire
14
15
4,107
2.58
20
12
20
6,530
1.62
25
10
30
10,380
1.02
40
8
40
16,510
0.641
55
6
55
26,250
0.410
80
4
70
41,740
0.257
105
Classifications
Solid Wire – They are single wire Stranded – They are group of smaller wires twisted to form a metallic string.
Receptacles
Raceway – It is the channel or wiring accessories so designed for holding wires, cables, or busbars that are either made of metal, plastic, or any insulating mediums. Conduit pipe is the most common electrical raceways used in all types of construction. Connectors – a metal sleeve usually made of copper that is slipped over and secured to the butted ends of conductors in making a joint. It is sometimes called splicing sleeve. Convenient Outlet or Attachment Cap – A A device that by insertion into a receptacles.
Wall Outlet – same as CO for attachment on wire coming from a lamps and other appliances. Lighting outlet – outlet intended for direct connection with a lamp holder, lighting fixtures, etc. Receptacle Outlet – outlet where one or more receptacles are installed. Junction Box – an extension of the box wiring. Receptacles – are contact device installed at the outlet for connection of a single attachment plug Switch – a device that open or closed the circuits in an electric circuit.
Ampacity of Electrical Conductor
It is the ability of the wire or conductor to carry current without overheating Conductor resistance to current flow generate not only heat but also contribute to the voltage drop Current size and rating should have sufficient ampacity to carry load. They should have adequate mechanical strength and should not be less than the rating of the branch circuit and the maximum load to be served.
Types of Cable
Armored Cable (AC) – used for both in exposed and concealed work Metal Clad Cable (MC) – used for service feeders, branch circuit, and indoor or outdoor work Mineral Insulated Cable (MI) – used for dry, wet or continuously moist location as service feeders or branch circuit. Non-Metallic Sheath Cable (NM) - used specifically for one or two family dwelling not exceeding 3 story buildings
Shielded Non-Metallic Sheath Cable (SNM) – used for hazardous location or in cable tray or or in in raceway. Underground Feeder and Branch Circuit Cable (UF) – used for underground connections including direct burial in the ground or feeder or branch circuit. Service Entrance Cable – primarily used for service wire.
Power and Control Tray Cable (TC) – used for installation in cable trays, raceways, or where it is supported by messenger wire. Flat Cable Assembly (FC) – for field installation in metal surface or raceways. Flat Conductor Cable (FCC) – used for general purposes such as appliance branch circuit, and for individual branch circuits especially in hard smooth continuous floor surface. Medium Voltage Cable (MV) – use for power system up to 3,000 volts.
Circular Mill
Mil is equal to 1/1000 of an inch that is used to measure the diameter of round wire. 1 circular mil = π /4 square mill = 0.7854 square mil Area, circular mil = D2 To find the circular mill area of any circle, just know the diameter in mils and then square this value.
Factors Determining Wire Size
Length Cross-Sectional Area
Materials
Resistance of Wire
R = 10.8 L / A (for copper) R = 17.0 L / A (for aluminum)
Where: R - wire resistance, ohms L - length of wire, ft A - area of wire, circular mills
Voltage Drop and Power Loss in Wire
Voltage Drop = Circuit Current x Resistance of Wire (I x R) Power Loss = Circuit Current x Voltage Drop (I x Vdrop) Power Loss = Component Resistance x Square of the Current (P = R x I2)
Allowable Voltage Drop
1% - used for branch circuit wires and loads involving constant voltage 2% - adequate design for practically all conditions 3% average design figure 5% used only if the economy of wire cost desired
Series Circuit
Series Connection - single path exist for current to flow; elements are arrange in series one after the other; no branches; current is the same but the voltage differ. Voltage: Vt = V1 + V2 + V3 … Resistance: Rt = R1 + R2 + R3 … Current: It = I1 = I2 = I3
Series Connection
Sample Problem Calculate the current flowing, the total resistance and the voltage drop across each resistor with the total applied voltage Et = 200 v and the value of each resistor is R 1 = 24 ohms, R 2 = 66 ohms, and R 3 = 44 ohms.
It
R1=24Ω
R2=66Ω
R3=44Ω
Et=200v
Given:Et - 200 volt
R1 - 24 ohms
R 2 - 66 ohms
R3 - 44 ohms
Required: Rt, It, voltage drop
Solution: Rt
= R1+R 2+R 3 = 24 ohms + 66 ohms + 44 ohms = 134 ohms
It
= Et / Rt = 200 v / 134 = 1.49 amp
ER 1
= It R 1= 1.49 amp x 24 ohms =
35.6 volt
ER 2
= It R 2= 1.49 amp x 66 ohms = 108.34 volt
ER 3
= It R 3= 1.49 amp x44 ohms = 65.56 volt
Parallel Circuit
Parallel Connection – multiple connection exist for current to flow; it is the standard arrangement for house wiring connection; voltage is the same but current differs. Voltage: Vt = V1 = V2 = V3 … Resistance: 1/Rt = 1/R1 + 1/R2 + 1/R3 … Current: It = I1 + I2 + I3 ...
Parallel Connection
Sample Problem The total voltage Et of 200 volts is the same across all three resistive branches, R 1is 40 ohms, R 2 is 100 ohms, and R 3 is 200 ohms. Calculate the current flowing in each resistive branches and also the total current.
R1=40Ω
Et=200v
R2=100Ω
R3=200Ω
It
Given:Et - 200 volt R 2 - 100 ohms Required: I1, I2, I3, It
R1 - 40 ohms R3 - 200 ohms
I1
= E / R1
= 200 v/40 ohms = 5 amps
I2
= E / R2
= 200 v/100 ohms= 2 amps
I3
= E / R3
= 200 v /200 ohms= 1 amps
It
= I1 + I2 + I3 = 5 amps + 2 amps + 1 amp = 8 amps
Branch Circuit
Electric Circuit – a complete path traversed by an electric current. Branch circuit – it is the circuit conductors between the final over current protective device and the outlet. It is the wiring installed between the circuit current protective device, i.e. fuse or circuit breaker, and the outlets.
Components of Branch Circuit
Source of voltage Wiring Load Switch and Fuse
Classifications of Branch circuit
General Purpose Branch Circuit – supplies outlets for lighting and small appliances including convenience receptacles. Appliance Branch Circuit – Supplies outlet intended for feeding appliances. Individual Appliance Branch Circuit – Intended to supply a single specific item.
Protection of Branch Circuit
Branch circuit should be protected from over current (any current in excess of the rated capacity of the equipment or the rated capacity of the conductor) . It should always be connected at its hot line and to the voltage source and its load end to the circuit wiring. Causes of over current
Overload in the equipment or conductors Short circuit or ground fault
Fuse – an overall current protection device with a circuit opening fusible element which open (break) when there is an over current in the circuit. Circuit Breaker - an over current protective device designed to function as a switch. It is equipped with automatic tripping device to protect the branch circuit from overload and ground fault.
Trip or tripping – refers to the cutting-off or disconnection of the current supply.
Factors to Consider in Designing Branch Circuit
Flexibility of the circuit Reliability and efficiency of service Safety of circuitry Economy as to cost Energy consideration Space allocation
Effect of Acquiring Low Cost Equipment
High energy cost High Maintenance cost
Shorter life
References
Brown, R. 1956. Farm electrification. McGrawHill Book Company. New York. 367pp. Subhash Metha. Electrical Engineering. Synergy Books International. A division of Sam Publishing Sdn. Bhd. 7 Jalan Bangsar Utama 3, Off Jalan Bangsar , Kuala Lumpur Malaysia. 388pp.
