It is important to replace a blown fuse with one of the correct current rating. What
would be the overall effect on a subcircuit if you used a replacement fuse that had:
(i) An under-rated current rating for the subcircuit it protects?
Give this one a try later!
The current rating is too low for the circuit, and could blow for no apparent
reason well below the circuit full-load current, that is, nuisance tripping
A rewireable fuse is being reloaded. State TWO reasons why it is important to thread
the fuse wire from terminal to terminal through the tortuous path in the fuse carrier.
Give this one a try later!
It prevents fuse element from bulging out the side of the carrier and being
accessible to touch. ● Under overload conditions the heat produced in the
, element is confined to the tunnel area. ● Under short-circuit conditions the
arc and molten element is confined within the fuse carrier and base.
State THREE advantages that HRC fuses have when compared to rewireable fuses.
Give this one a try later!
It will safely interrupt short circuit currents of much higher values.
● It eliminates arcing because the fuse element is sealed.
● It is obtainable in a range of Utilisation category (fusing factors).
● Current rating is clearly marked.
● Reliable operation within prescribed limits.
● Constant fusing characteristics.
● Faster operation/acting.
● Doesn't deteriorate over time.
In an office, a 16A MCB protects a final subcircuit consisting of three socket outlets
supplying various 230V plug-in electrical appliances. The appliances were operating
normally until the MCB tripped. When the MCB was reset, it tripped again. You have
established that:
● The MCB is correctly rated for the circuit and is not faulty.
● The circuit is not faulty.
● The appliances are not overloading the circuit
(i) State the TWO reasons why the MCB keeps tripping.
For ONE of the reasons you have stated in (i), describe how you would test to
establish that this is the reason why the MCB keeps tripping.
Give this one a try later!
1.
● A short to earth in an appliance. (1 mark)
● A short between active and neutral in an appliance.
2.
Use an insulation resistance tester.
On each appliance, carry out an insulation resistance test between active
and the frame of the appliance. (2 marks) - The test result should
would be the overall effect on a subcircuit if you used a replacement fuse that had:
(i) An under-rated current rating for the subcircuit it protects?
Give this one a try later!
The current rating is too low for the circuit, and could blow for no apparent
reason well below the circuit full-load current, that is, nuisance tripping
A rewireable fuse is being reloaded. State TWO reasons why it is important to thread
the fuse wire from terminal to terminal through the tortuous path in the fuse carrier.
Give this one a try later!
It prevents fuse element from bulging out the side of the carrier and being
accessible to touch. ● Under overload conditions the heat produced in the
, element is confined to the tunnel area. ● Under short-circuit conditions the
arc and molten element is confined within the fuse carrier and base.
State THREE advantages that HRC fuses have when compared to rewireable fuses.
Give this one a try later!
It will safely interrupt short circuit currents of much higher values.
● It eliminates arcing because the fuse element is sealed.
● It is obtainable in a range of Utilisation category (fusing factors).
● Current rating is clearly marked.
● Reliable operation within prescribed limits.
● Constant fusing characteristics.
● Faster operation/acting.
● Doesn't deteriorate over time.
In an office, a 16A MCB protects a final subcircuit consisting of three socket outlets
supplying various 230V plug-in electrical appliances. The appliances were operating
normally until the MCB tripped. When the MCB was reset, it tripped again. You have
established that:
● The MCB is correctly rated for the circuit and is not faulty.
● The circuit is not faulty.
● The appliances are not overloading the circuit
(i) State the TWO reasons why the MCB keeps tripping.
For ONE of the reasons you have stated in (i), describe how you would test to
establish that this is the reason why the MCB keeps tripping.
Give this one a try later!
1.
● A short to earth in an appliance. (1 mark)
● A short between active and neutral in an appliance.
2.
Use an insulation resistance tester.
On each appliance, carry out an insulation resistance test between active
and the frame of the appliance. (2 marks) - The test result should
