Part P Circuit Design and Protection

Question 1

When designing a ring final circuit for a domestic kitchen, what is the minimum cable size for 2.5mm² twin and earth cable with standard installation method?

Accepted Answer

2.5mm²

Answer

1.0mm²

Answer

1.5mm²

Answer

4.0mm²

Question 2

What is the purpose of applying correction factors when calculating the current-carrying capacity of a cable?

Accepted Answer

To account for conditions that reduce the cable's ability to dissipate heat, such as thermal insulation, ambient temperature, and grouping

Answer

To increase the cable's capacity so smaller cable can be used

Answer

To determine the voltage drop

Answer

To calculate the prospective fault current

Question 3

A radial circuit for a domestic cooker uses 6mm² cable protected by a 32A MCB. What is the maximum demand that should be calculated for a 13kW cooker using diversity?

Accepted Answer

10A plus 30% of the remainder plus 5A for a socket outlet

Answer

13kW (full rated load)

Answer

6kW flat rate

Answer

32A × 230V = 7.36kW

Question 4

What is the maximum permitted voltage drop for a lighting circuit in a domestic installation according to BS 7671?

Accepted Answer

3% of the nominal voltage (6.9V)

Answer

5% of the nominal voltage (11.5V)

Answer

10% of the nominal voltage (23V)

Answer

No limit specified

Question 5

In a domestic installation, what is the typical prospective fault current (PFC) range at the origin of supply?

Accepted Answer

3kA–16kA

Answer

100A–500A

Answer

1kA–3kA

Answer

20kA–50kA

Question 6

Which type of MCB (circuit breaker) is most commonly used in domestic installations?

Accepted Answer

Type B — trips at 3–5 times rated current

Answer

Type A — trips at 2–3 times rated current

Answer

Type C — trips at 5–10 times rated current

Answer

Type D — trips at 10–20 times rated current