Part P Cable Selection and Wiring Systems 2

Question 1

When a cable is totally enclosed within thermal insulation (e.g., loft insulation), what derating factor must be applied to its current-carrying capacity?

Accepted Answer

0.5

Answer

0.25

Answer

0.75

Answer

No derating is required

Question 2

According to BS 7671 Appendix 12, what is the recommended maximum voltage drop for a lighting final circuit in a domestic installation?

Accepted Answer

3% (6.9 V)

Answer

1% (2.3 V)

Answer

5% (11.5 V)

Answer

10% (23 V)

Question 3

Which BS 7671 reference installation method applies when twin and earth cable is clipped directly to a plaster wall surface?

Accepted Answer

Reference Method C

Answer

Reference Method A

Answer

Reference Method B

Answer

Reference Method E

Question 4

What is the recommended minimum burial depth for a cable installed under a domestic garden or lawn (not subject to vehicle traffic)?

Accepted Answer

500 mm

Answer

150 mm

Answer

300 mm

Answer

750 mm

Question 5

When two or more circuits share the same conduit, trunking, or cable bundle, what effect does this have on each cable's current-carrying capacity?

Accepted Answer

It must be reduced using a grouping derating factor

Answer

It increases, as the cables share the generated heat

Answer

It remains unchanged

Answer

It doubles as the circuits share the enclosure

Question 6

Which cable type provides inherent mechanical protection suitable for direct burial or outdoor above-ground runs without requiring additional conduit?

Accepted Answer

Steel Wire Armoured (SWA) cable

Answer

Flexible cord (3183Y)

Answer

Fire-resistant cable (FP200)

Answer

Standard flat twin and earth cable

Question 7

What minimum cable cross-sectional area (CSA) is typically required for a domestic cooker circuit supplying a 45A cooker control unit?

Accepted Answer

10.0 mm²

Answer

4.0 mm²

Answer

6.0 mm²

Answer

16.0 mm²