Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning a domestic 100A electrical installation and circuit protection, is answered by SELECT:
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| A BS 3871 MCB - typically 6kA rated. |
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Question: Would we be allowed to use 3kA MCBs at the origin of a domestic 100A installation if the fault current exceeded the 3kA.
I have read that if the consumer unit enclosure is type-tested to 16kA, then the supply company's main fuse will suffice up to 16kA. Is there a minimum size breaking capacity for a MCB at the origin of a domestic electrical installation?
Answer: Normally, the short circuit capacity of circuit breakers (BS EN 60898) used in domestic installations are rated at 6kA and BS 3871 MCBs for domestic use were typically M6 rated which also equates to 6kA.
In a domestic installation, where the distributors cut-out fuse is either a BS 88 or BS 1361 type and does not rated at greater than 100A, the cut-out fuse may be able to provide the appropriate short circuit protection it is however preferable if the fault rating of the circuit breakers is sufficinet to clear any fault occurring.
It should be noted that a protective device should generally be selected in relation to the likely fault current at the position installed.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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