RCD Testing Problem

[cosmarchy]

Hi,

I'm testing an installation and all of the tests have gone well until the RCD rest on the upstairs ringmain.

The ring main itself is a loop of 9 sockets - the phases are a loop, as is the neutral and the cpc, all with suitable continuity resistance. The insulation resistance test is also suitably high.

When I plug in the RCD tester (megger CBT3) the P-N and P-E light up but the screen displays >50v which according to the manual means there is a N-E voltage greater than 50v. So I checked this with a multimeter and there is indeed a voltage present; 230v WTF :shout::shout::shout:

Now this sounds to me like a dicky neutral or earth but I've had the entire ring apart, checked connections, checked for ring again, checked IR again, checked the consumer unit terminations.
I also considered a dodgy tester but it functions for the downstairs ring and kitchen ring so I think I can eliminate that possibility.

Can anyone offer some suggestions?

Thanks

 

[ashrow]

You checked the Ze at the head ?

 

[telectrix]

i would suspect connections in CU. have you caught the insulation on either the cpc or N? is the busbar properly into the MCB? sometimes it can go behind the clamp and make a poor connection.

 

[ian.settle1]

You checked the Ze at the head ?

What may I ask has the Ze got to do with him measuring 230v across N-E?

 

[SYKRAPS]

Connections that are factory fit at the RCD crossed or RCBO cable connections back to front maybe

 

[Nightmare1308]

Have u tryed doing a continuity test of Rn+R2 as a figure of 8 then gone round see if any readings jump then u will see the socket at fault ?

 

[tony mc]

I would imagine that if the ZE (RA) is high then the meter will not test the RCD as the touch voltage will exceed 50 volts so the test meter will not function?

What is the earthing arrangement etc?

A bit more info is need !

 

[Richard Burns]

Do you have anything plugged into the ring that may be faulty and causing the N-PE voltage, thoguh this shoudl have been found on the IR testing?

I would tend toward Tel's response that the fault is at the CU since there seems to be no fault on the ring when it is not connected to the CU.

 

[kamikizzy]

I would guess fault at cu check all primary connections first

 

[Farmelectrics]

Induced voltage maybe

 

[cosmarchy]

Just a quick one to say I have found the solution, in case anyone else has something similar.

Turns out, the neutral of this circuit went to the wrong RCD neutral bar (split load CU) :38:

May be helpful if someone comes across this.

Thanks all for your suggestions, they were much appreciated.

 

[Spudnik]

Glad you got it sorted, however, i would have thought the RCD wouldnt even hold if the N was incorrectly connected.

 

[SPARTYKUS]

I hate dual RCD boards. Just go for the cheap RCBO boards now

 

[ashrow]

i am with Jason on this, i have never come across (yet) where the neutral incorrectly installed/connected at DB would when tested or put under load fail to trip etc
But glad you go sorted

off topic
I personally prefer individual rcbos when the client dont mind the cost (my last 2 big jobs had a total of 163 HAGER rcbos in their 3phase boards)

 

[Engineer54]

I hate dual RCD boards. Just go for the cheap RCBO boards now

Agree wholeheartedly!! Dual 17th boards as they are called and even the the so called (and ill named) ''high integrity'' dual boards, are nothing more than a compromise, ...A compromise on cost, and a compromise on electrical integrity and safety!! Apart from anything else, they can be a complete pain when trying to locate a fault (especially a leakage fault) on one of the protected circuits.

When all said and done, you can't get a higher integrity in a CU layout, than an all RCBO board!!!