Discuss loop impedence test in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net
Anyway the point is rather moot lol, why would you have a Zs of 7.6k on a TN system anyway ? Rhetorical question BTW lol
Hi guys I was wondering if someone can help me with a question on my 2394 paper it says:
Why is it necessary to carry out an earth fault loop impedence test before carrying out an RCD test
My answer:
Because an earth fault loop impedance test will prove that there is a fault path to earth and without a fault path to earth an RCD cannot operate as they only operate when a live to earth or neutral to earth fault occurs.
If you could tell me if im correct or not in what im saying and if im correct do i need to elaborate a bit more
Thanks
2394 initial verification. As I understand it, you shouldn't be energising anything until you've confirmed there's an EFLI that complies.
OK then,
I was taught that the reason we use the max TT Zs values as the worst case for TN systems where RCDs are concerned, because even where the reason for the RCD is for say a high-ish Zs (just over the OCPD threshold) a TN system should always still have a lower Zs than most common TT systems (E54's TT excluded lol).
So long as you complied within the worst case TT values it would be ok with TN systems, which by default should have a much lower Zs anyway than those given in the TT table, and if you do have happen to have values approaching the max given in the TT tables on a TN system then you have other more serious faults. lol
You do realise that the EFLI is a live test ?
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