Part P BS 7671 IET Wiring Regulations 2

Question 1

What is the fundamental protection against electric shock in BS 7671?

Accepted Answer

Basic protection (preventing contact with live parts) and fault protection (stopping dangerous current in the event of a fault)

Answer

BS 7671 requires two levels of shock protection: basic protection (preventing access to live parts under normal conditions, e.g., insulation) and fault protection (limiting shock current if a fault occurs, e.g., earthing and protective devices).

Question 2

What does the term 'protective bonding' mean in BS 7671?

Accepted Answer

Connecting extraneous conductive parts to the main earthing terminal to prevent dangerous potential differences

Answer

Protective bonding (main and supplementary) connects extraneous metallic parts (such as gas pipes, water pipes, structural steelwork) to the main earthing terminal, preventing dangerous voltage differences during a fault.

Question 3

What is the minimum disconnection time for a circuit with a fault to earth in a TN system supplying a socket outlet circuit not exceeding 32 A?

Accepted Answer

0.4 seconds

Answer

BS 7671 Table 41.1 requires a maximum disconnection time of 0.4 seconds for socket outlet circuits up to 32 A in TN systems, to limit the duration of dangerous touch voltages in the event of a fault.

Question 4

What does 'Zs' represent in electrical installation testing?

Accepted Answer

The total earth fault loop impedance of the circuit

Answer

Zs is the total earth fault loop impedance, comprising the supply source impedance (Ze) plus the impedance of the phase and protective conductors of the circuit (Zs = Ze + (R1 + R2)).

Question 5

What test instrument is used to measure earth fault loop impedance?

Accepted Answer

An earth fault loop impedance tester

Answer

An earth fault loop impedance tester injects a current pulse around the fault loop path and measures the impedance (Zs), which is compared to the maximum values in BS 7671 to verify protective device operation.

Part P Electrical Practice Test

Part P Electrical Practice Test

Part P BS 7671 IET Wiring Regulations 2