c A flex outlet is a wall outlet which has a flexible cable permanently wired into it instead of being fitted with a plug to go into a socket outlet. Flex outlets have their own fuse holder to replace the fuse which would normally be fitted into the plug if a fused plug were used instead. Such fused flex outlets are commonly used for electrical appliances which will never be moved, such as immersion heaters, which are permanently installed into domestic hot water storage tanks, and hot water heaters which are wall-mounted. A spur outlet is an additional wall outlet that is permanently connected to another wall outlet instead of being wired directly back to the breaker panel on its own circuit. Spur outlets are used occasionally when most socket outlets in a building are installed on a "ring main" and for some reason - usually because of cost when an additional socket outlet is found to be needed at a new point in the building it was decided not to extend the ring main itself to that point in the building. A "ring main" is a loop of cable that goes out from a breaker to feed a "ring" of socket outlets in part of a building and then returns to be connected back to the same breaker. For instance in an averagesized house 3 ring mains would normally be installed: one for the socket outlets in the kitchen, one for the rest of the ground floor and the third for the bedroom floor. This method is used extensively in the UK and Eire where every appliance has its own correctly-fused plug.
Ô In electrical power distribution network how to decide the diversity factor? when a] If power supply is available 24 hours . b] If power supply is available for certain period of 24 hours. ANSWER:
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In electrical power distribution, a is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. The size of the busbar determines the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 mm2 but electrical substations may use metal tubes of 50 mm in diameter (1,963 mm2) or more as busbars, and an aluminum smelter will have very large busbars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminum from molten salts.
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V Busbars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross-sectional area ratio. The skin effect makes 50±60 HzACbusbars more than about 8 mm (1/3 in) thick inefficient, so hollow or flat shapes are prevalent in higher current applications. A hollow section has higher stiffness than a solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoor switchyards. A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal earthed enclosure or by elevation out of normal reach. Neutralbusbars may also be insulated. Earthbusbars are typically bolted directly onto any metal chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway, segregated-phase bus, or isolated-phase bus. Busbars may be connected to each other and to electrical apparatus by bolted or clamp connections. Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the contact resistance. At extra-high voltages (more than 300 kV) in outdoor buses, corona around the connections becomes a source of radio-frequency interference and power loss, so connection fittings designed for these voltages are used. Busbars are typically contained inside of either a distribution board or busway. V Ú
ºistribution boards split the electrical supply into separate circuits at one location.
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Busways, or bus ducts, are long busbars with a protective cover. Rather than branching the main supply at one location, they allow new circuits to branch off anywhere along the route of the busway.
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The busbars contained within are visible in this opened busway, above the arrows at left and traveling horizontally at right. This busway section was used in a fire test of a firestop system, achieving a 2 hour fire-resistance rating.
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Bus duct penetration, awaiting firestop.
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Electrical conduit and bus duct in a building at Texaco Nanticoke refinery in Nanticoke, Ontario, 1980s.
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= Current Carrying : 300 Amps operating current @ 30°C max temp rise. Application Dependent Parameters: Minimum Voltage drop, Max Capacitance, Minimum inductance. Product Configuration: Two Layer, Rigid Epoxy Glass Board, Edge Potting; Shape: Planar Dimensions: 24" long by 1.5" wide max Materials: Copper alloy 110, Mylar Tedlar Inner Insulation Termination Method: Threaded Fastener Mounting Method: Insulated thru holes Environment: High humidity environment, minimum vibration
Cross Sectional Area
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A = 300 x l x [1 + 0.75(N-1)] formula (2.7)
A = 0.097 sq in
l = 300 amps N = 2 layers
A = 300 x 300 x [1 + 0.75(2-1)]
Conductor Width (w) & Thickness (t)
w=A/t formula (2.8)
t = 0.093" w = 1.032"
t = selected thickness values from the available std thickness to get the maximum w / t ratio and practical to the application A = 0.097 sq in Thickness (t)
0.125"
0.093"
0.062"
Width (w)
0.776"
1.043"
1.564"
w /t Ratio
6.20
11.21
25.23
The width requirement is 1.5" max therefore 11.21 (0.93"/1.043") is the max w / t ratio practical to the application
Resistance
(Optional method) Use the ampacity table and select the combination of w & t practical to the application and which will yield the lowest inductance (max w / t ratio)
t = 0.093" w = 1.040"
R = ȡ / A ohms/foot
R = 0.084
formula (2.1)
Milli ȍ / foot @ 20°C
ȡ = 8.1 (ȍ sq mil/ft) at Ambient Temp. 20°C table 3 A = 96,750 sq mil
R = 8.1 / 96,750 ȍ/foot
R2 = R1 [1 + Į (T2-T1)] ohms/foot formula (2.2)
R2 = 1.074 Milli ȍ / foot @ 50°C
R1 = 0.084 Milli Ohms as calculated above Į = .393 from table 3 (T1-T2) = 30°C
R2 = 0.084 [(1 + 0.393(30)]
Voltage Drop
ǻV = R x x l formula (2.3)
ǻV = 48 MIlli volts @ 20°C
(Conductor length) = 2 ft R = 0.084 Milli Ohm / foot at ambient temperature l = 300 Amps
ǻV = 0.084 * 2 * 300 = 50.4 Milli Volts at ambient temperature
R2 = 1.074 Mili Ohm / foot at the 50°C (the max allowed temperature)
ǻV = 0.644 Volts @ 50°C
ǻV = 1.074 * 2 * 300 (if this voltage drop is too large, increase cross sectional area)
Capacitance
C = 0.224 (k)(w)( )/d picofards formula (2.4)
C = 0.0095 microfarads
K (Dielectric constant Mylar tedlar) = 8.5 from table 4 w (width) = 1.040" (length) = 24" d (dielectric thickness) = 0.005"
C = (0.224)(8.5)(1.040)(24)/.005
Inductance
L = 31.9 ( ) (d/w) nano Henrys
3.68
formula (2.5)
nanoHenrys
= 24" d = .005 w = 1.040
L = 31.9 (24) (.005/1.040)
=!= "# ! !$ Equipotential Bonding³The Key to Building Safety Equipotential is a complex word that simply means equalizing electrical potential. Equipotential bonding is the process of making an electrical connection between the grounding electrode and any metal conductor³pipes, plumbing, flues, etc.³that may be exposed to a lightning strike and become a conductive path for lightning energy. Currently, in the United States, the National Electrical Code does not require equipotential bonding for all metal systems in the house. The NEC does require bonding of major metal systems, such as water piping, structural metal beams, and communications lines. In Europe, equipotential bonding for the entire building and all appliances is the norm. According to Source IEC Session 20 ² Earthing/Grounding Regulations: ´Full equipotential bonding is achieved by connecting not only the housings of the electrical equipment into the equipotential bonding, but also all other accessible, conductive structural parts such as building construction, metal containers, piping, etc. Extraneous conductive parts which do not belong to the structure or installation of the system (e.g. door frames, window frames) need not be incorporated into the equipotential bonding. This also applies to housings if their method of fixing provides reliable contact with structural parts for piping already involved in equipotential bonding. The connections for equipotential bonding must be reliable, e.g. using secured screw terminals." By effectively connecting all metal systems in the house together to the building·s electrical ground, the chances of electrical arcing caused by unintended voltage surges from lightning or transformer failures are significantly reduced or eliminated. Areas of the United States and Canada that require bonding of mechanical and electrical systems have no history of damage to CSST as a result of lightning. Perhaps someday, equipotential bonding will be part of building codes in the United States. Until then, installing CSST piping with enhanced lighting protection and bonding as required by local codes offers optimum protection against the effects of indirect lighting strikes.
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!uses and circuit breakers are two different ways of protecting against suddenly large overloads of electrical flow. Large power overloads are dangerous, potentially destroying electrical equipment or causing a fire. Both fuses and circuit breakers will automatically block against an incoming surge of electrical power past a certain safety limit. But while they both accomplish the same task, each uses different technology in the way that it stops the flow of electricity. !uses are typically small objects that plug into a fusebox or other central location. They are an early technology, dating back to the 19th century. Inside the fuse is a small piece of metal, across which the electricity must pass. ºuring normal flow of electricity, the fuse permits the power to pass unobstucted. But during an unsafe overload, the small piece of metal melts, stopping the flow of electricity. When a fuse is tripped, it should be thrown away and replaced with a new fuse. As there are many varities of fuses available that handle different capacities of electricity, care should be taken when choosing replacement fuses. Circuit breakers are a more recent invention and improve on fuse technology. Circuit breakers are switches that are tripped when the electrical flow passes a safe limit. The excess of electricity typically triggers an electromagnet, which trips the circuit breaker when an unsafe limit is reached. Once tripped, the switches simply turn off. That stops the flow of electricity, which will remain off until the switch is reset. To reset the flow of electricity after the problem is resolved, the switch can simply be turned back on. Circuit breakers are often located in a cabinet of individual switches, typically inside of an apartment or other central place. While often used in homes, circuit breakers can be used for much larger industrial applications as well. !uses and circuit breakers have unique advantages and disadvantages. One advantage of fuses is that they are cheap and can be purchased from any hardware store, but they have the drawback of needing to be replaced once they stop an overload. That can be challenging in a darkened room. Alternatively, circuit breakers can simply be reset with a flip of a switch after an overload. However, the technology can be more expensive than a fusebox. Electricians are best qualified to determine whether fuses or circuit breakers are better for a particular electrical installation.
