Chris Allen asks this question, which is about whether 6kA MCBs in a consumer units are OK, and whether the main fuse will provide sufficient protection. It has been answered by the NICEIC (Theme – Fire, Safety and Security):
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Question: Whilst carrying out a recent EICR, I noted that the measured prospective fault current (PFC) at the origin was quite high at 13.3kA.
I need to know whether or not the MCBs rated at 6kA in the consumer unit connected directly to the source of supply are compliant?
In other words, is it OK to rely on the supply authority fuse to provide PFC protection, or should there be a fuse on the consumer side of the installation before the consumer unit?
Please note that I could not see a kA rating on the main switch in the consumer unit to check whether or not this would provide adequate protection.
Answer: Indeed your thoughts are correct and although the equipment in the consumer unit is rated at a lower kA, the supplier’s fuse will deal with this issue as a means of protection.
If you have a copy of Guidance Note 5 'Protection against electric shock', there is in-depth help provided in it on this topic.
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