46185280 iee wiring regulation
DESCRIPTION
IEE WIRING REGSTRANSCRIPT
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IEE Wiring Regulations
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Designing an electrical installation
Assessment of general characteristicPurpose and intended use of the building and the type of constructionMaximum current demandCompatibilityMaintainability
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PROTECTION AGAINST ELECTRIC SHOCKS
Direct Contact
An electric shock result from contact with a conductor which forms part of a circuit and would be expected to be live.
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DIRECT CONTACTL
N
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PROTECTION AGAINST ELECTRIC SHOCKS
Indirect contact
An electric shock is received from contact with something which would not normally be expected to be live but has become so as a results of a fault.
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INDIRECT CONTACTL
N
E
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PROTECTION AGAINST ELECTRIC SHOCKS
Protection against direct contactThe insulation of live partsThe provision of barrier, obstacles or enclosure to prevent touchingPlacing out of reach
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PROTECTION AGAINST ELECTRIC SHOCKS
Protection against indirect contact
Making sure that when a fault occurs the supply being cutoff within a safe time using
An over-current protection devicesA residual current devices (Current operated trip switch)
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Protection with over-current devices
L
N
Protective conductor
Fuse/MCB
Substation earth
Earth fault loop
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Earth fault loop impedance
Phase conductor impedanceT/F leakage impedanceT/F earth resistance including protective conductorResistance of the earthResistance of the consumers earth electrodeProtective conductor impedanceFault impedance
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Fixed and portable equipment
Portable equipmentShould disconnect the
supply within 0. 4 s
Fixed equipmentShould disconnect the
supply within 5 s
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Operation criteria for a fuse
Fusing current < Fault currentFusing current
For a portable appliance fusing current for 0.4 s operation For a fixed equipment fusing current for 5 s operation
Fault current = Nominal voltage / Earth fault loop
impedance
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Fusing characteristic
5 sec operating time for a 30 A fuse = 130 AMaximum allowable earth fault loop impedance = .....
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Over-current
240V
0.1
0.150
A
C
B
5A wire
CALCULATENormal current in the circuitCurrent when B & C are short circuited due to a faultCurrent when there is a direct short circuit between A & C
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Over-current and short circuit current
Over-current: current higher than that is intended to be present in the system
Short circuit current: Occur under fault conditions and may be very high
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Protection against overload current
Overload current should be interrupted before a temperature rise cause damage to the insulation, joints etc.Devices that can be used:
Semi-enclosed fusesHigh breaking capacity fusesMiniature and moulded case circuit breakers (MCB and MCCB)
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Selection criteria of the protective device for overload
Protective device .. Nominal current (In)Operating current (I2)I2 > In
Cable ... Current carrying capacity (For the smallest cable Iz)Designed current or load current (Ib)
Ib < In < IzI2 < 1.45 x Iz
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Semi-enclosed fusesRated current (In) value of current which the fusing element can usually carry without meltingMinimum fusing current (I2) minimum value of the current at which the fuse element meltsFusing factor = I2/In 2In2 d3 ( d diameter of the fuse wire)
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HBC fusesHBC fuses has quenching materials inside to quench the arc produced during the breaking processBreaking capacity --- 10 20 kA
Fusing element
Filling powder
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Miniature circuit breaker (MCB)
MCB is fitted withMagnetic coil for very fast operation under short circuitBimetallic strip for slow operation for overload currents
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Miniature circuit breaker (MCB)
100
101
102
10-3
10-2
10-1
100
101
102
103
Current as a multiple of plug setting
T
i
m
e
i
n
s
e
c
f
o
r
T
M
S
=
1
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Moulded case circuit breaker (MCCB)
Rating can be adjusted
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Protection against short circuit
Fault current is very highBreaking capacity of the protective device > Fault currentThe fault current protection system must operates before there is damaging increase in conductor insulation temperatureTime to damage a cable 2
2
IAt