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Needing to meet mcb zs with ln loop.
Former Community Member
Where an rcd is relied on for fault protection due to high zs it has been suggested to me that the loop between live Conductors needs to be less than the mcb max zs. I can't find anything on this anywhere but he said he had this confirmed by an niceic assessor. Have I got it wrong ?
but the required clearing time for an L-N fault is much longer than for an L-E fault, where we would have to worry about touch voltages, and insist on ADS in a fraction of a heartbeat. There is no formal time limit in BS7671, but If you are thinking it ought to be no more than a few seconds however, then you can deduce a new, much higher level of L-N loop impedance that is the upper acceptable limit.
but the required clearing time for an L-N fault is much longer than for an L-E fault, where we would have to worry about touch voltages, and insist on ADS in a fraction of a heartbeat. There is no formal time limit in BS7671, but If you are thinking it ought to be no more than a few seconds however, then you can deduce a new, much higher level of L-N loop impedance that is the upper acceptable limit.
