BS7671: Part 4 - 10 Questions

1. A 230 V single phase circuit supplying a pump motor is protected by a 20 A type C circuit breaker to BS EN 60898. The minimum value of fault current to ensure compliance with the thermal and shock requirements is:

• a) 20 A

• b) 140 A

• c) 100 A

• d) 200 A

2. Given that the fault current on a 16A BS 88 fuse is 60A, the corresponding disconnection time is:

• a) 0.5 s

• b) 1 s

• c) 3 s

• d) 10 s

3. From the time/current characteristic for a 30A BS 3036 fuse, the approximate current required to operate this device at a time of 5 s is:

• a) 30 A

• b) 66 A

• c) 87 A

• d) 180 A

4. A 15A protective device to BS3036 when carrying a fault current of 180A has an operating time of:

• a) 0.4 s

• b) 0.2 s

• c) 0.1 s

• d) 5 s

5. A 30A protective device to BS1361 when carrying a fault current of 200A will operate in:

• a) 0.2 s

• b) 4 s

• c) 0.4 s

• d) 5 s

6. The symbol used to denote the operating current of the device protecting a circuit against overload is:

• a) lb

• b) l2

• c) ln

• d) lz

7. A 230 V 30 A radial circuit is protected by a BS 3036 device. If the value of earth loop impedance for the circuit is 2.3Ω, disconnection under Line/earth fault condition will occur in:

• a) 2 s

• b) 4 s

• c) 3 s

• d) 5 s

8. The fault current due to an earth fault of negligible impedance in a 400V, threephase four-wire circuit having an earth loop impedance of 0.3 Ω is:

• a) 1383 A

• b) 728.3 A

• c) 124.5 A

• d) 72 A

9. A single-phase circuit is to be wired using single-core cables having 90º C thermosetting insulation with copper conductors and protected by a BS 3036 protective device. For an ambient temperature of 55º C, identify which of the following is the ambient temperature rating factor to be used when determining the size of the conductor.

• a) 0.61

• b) 0.76

• c) 0.88

• d) 0.84

10. A circuit with a design current of 45 A is installed using a cable with a current rating of 50 A. If the voltage drop for the cable is 8.0mV/A/m, the circuit voltage drop for a 10 m run will be:

• a) 2.5 V

• b) 3.6 V

• c) 4 V

• d) 6 V