This Question of the Day concerns separate circuit protective conductors (CPCs) run in parallel with armour. It is answered by BASEC (Theme – Cables and Wiring):
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This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: I've just been reading an article regarding a research program by another organisation, which states that, following results of tests, in most cases a separate CPC run in parallel with the armour is not necessary.
Can anyone tell me whether this is now the case? I understand the research was commissioned in 2007.
Answer: In many applications, the amount of armouring present on an armoured cable will be of sufficiently low resistance to permit its use as an acceptable CPC.
However, where a full-conductor-sized CPC has been specified, or where other considerations apply, this will not be the case and a separate CPC should be installed. It will depend on the actual system design and should be specified by the designer. Calculations should be carried out whenever the armour is used as a CPC to make sure.
The armouring would, of course, need to be properly terminated through appropriate glands at both ends, and tested as normal for a CPC.
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