Hi Zs reading

[chloebear]

I have a new ring circuit on a 32amp 'B' type breaker protected by a 30mA rcd in the CU. The Zs reading I am getting for the circuit is higher than the max allowed - max = 1.44 and I am getting readings of 1.51 - is the circuit alowable under the BS regs as it is protected by an Rcd???????????????

 

[rocker]

Have you got it on an RCD?

 

[Guest123]

Technically yes, but if as you say it is a new ring final then I would expect it to be well within the max permissable limits for the MCB alone.


Have you just installed it?, is it a particularly long circuit???

 

[rocker]

Just re-read.... max Zs is technically 1667 ohms though you wouldn't want to get near that. If it's a fairly big ring, I wouldn't be bothered with 1.51

 

[chloebear]

Yes newly installed in a fair sized new build, but not an overly long circuit.

 

[rocker]

Do us a flavour and do a Ze measurement at the board from tails, then from the load side of the RCD, and make sure they are about the same - have had it once or twice when an otherwise fine RCD ups Zs readings, even though they are not offering up more resistance. Don't knnow why this happens actually, if anyone has any ideas?

 

[nickblake]

What i would do is a quick check of the connections also carry out a few Zs tests around the ring see if the reading are higher than normal hi Zs could well be a loose connection although as rocker has said technically its fine as its protected by an RCD but its nice to get it within the regs limits , oh and just for the record you measured Zs should be lower than the max 80% of the maximum laid out in BS7671 if im not mistaken probably am brains not engaged as yet

thats a good point rocker if the Ze is higher than it should be then this will also effect the readings