Discuss Zs reading high! in the Australia area at ElectriciansForums.net
first compare it with another meter if you have a mate with one. i would still be inclined to suspect MCB or RCD is adding that 0.7 ish value.
Thanks for the replies guys.
Absolutely right Rockingit. I will not be happy having spent £500 on a new Megger if I can't trust it's readings, or get readings that are above the max Zs allowed by BS7671 when it shouldn't be. Yes there are tolerances for test results but +/- 5% not + 250%.
To clear up a couple of matters the supply is TNCS, the length of cable is about 20 metres (8 metres of 6mm T+E inside cavity wall upto loft, then into 60 amp juntion box joined to 10mm through isolator to shower.) Yes 0.91 is just OK for the 40 amp MCB but it's very close.
As I said earlier I also got high readings on the cooker circuit 101 when it should have been 0.32 and radial sockets 106 should have been 0.53.
I'm starting to think I may need to send the meter back to have it checked.
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