05: 52 Selection and Erection of Wiring Systems (136)

Question 1

If running cables in permitted zones are used as protection against impact, what extra measure would be required if the installation was in a domestic premises. (522.6.202 p.139) (415.1.1 p.73)

a) Run cables with capping fitted
b) All circuits protected with a 30mA RCBO
c) Cables to have additional protection by means of 30 mA RCD
d) Cables to have additional protection by means of 100 mA RCD

Answer 1

c) Cables to have additional protection by means of 30 mA RCD

522.6.202 p139
A cable installed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition shall:

(i) be installed in a zone within 150 mm from the top of the wall or partition or within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined from the reverse side, a zone formed on one side of a wall of 100 mm thickness or less or partition of 100 mm thickness or less extends to the reverse side, or

(ii) comply with Regulation 522.6.204.
Where indent (i) but not indent (ii) applies, the cable shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.

Question 2

Cable surrounded by thermal insulation for 400 mm or more has a derating factor of (523.9 p.143 Table 52.2 p.144)

a) 0.63
b) 0.51
c) 0.55
d) 0.5

Answer 2

b) 0.51

523.9 p.143
Cables in thermal insulation:

Where a cable is to be totally surrounded by thermal insulation for less than 0.5 m the current-carrying capacity of the cable shall be reduced appropriately depending on the size of cable, length in insulation and thermal properties of the insulation. The derating factors in Table 52.2 are appropriate to conductor sizes up to 10 mm2 in thermal insulation having a thermal conductivity (λ) greater than 0.04 Wm-1K-1.

Question 3

Every connection shall be accessible for inspection except for (526.3 p.145)

a) A joint that has been thoroughly inspected and tested
b) A joint designed to be buried in the ground
c) A joint in a class 2 junction box
d) A joint that cannot be reasonably be located to comply with that regulation

Answer 3

b) A joint designed to be buried in the ground.

526.3 p.145-146
Every connection shall be accessible for inspection, testing and maintenance, except for the following:

(i) A joint designed to be buried in the ground
(ii) A compound-filled or encapsulated joint 146

(iii) A connection between a cold tail and the heating element as in ceiling heating, floor heating or a trace
heating system

(iv) A joint made by welding, soldering, brazing or appropriate compression tool
(v) Joints or connections made in equipment by the manufacturer of the product and not intended to be inspected or maintained
(vi) Equipment complying with BS 5733 for a maintenance-free accessory and marked with the symbol MF and installed in accordance with the manufacturer’s instructions.