rcd tripping when power restored after power cut

[steve1999uk]

Hi all i have a customer who has a problem that when they have a power cut and the power is restored the rcd trips i have done full test on the system a ramp test on rcd and even disconnected everything except the incoming tails and when i replicate the power cut it still trips. It is a crabtree starbreaker split load metal clad consumer unit the rcd is the rccb 63amp type. Insulation test done on all circuits and was fine have even swapped rcd for another same type etc and still trips .customer spends a lot of time out of the country on business and is worried about freezer etc if they have a power cut any help in this matter would be greatly appreciated

 

[Marvo]

Did you check the standing leakage with an earth leakage clamp meter around L+N? How many PC's do they have?

You could install an RCBO on the circuits that are critical but that's not really fixing the problem. I'd start with a global leakage test then if it's pretty low (<10mA) I'd just try a replacement RCD out of interest. If that didn't help I'd disconnect circuits one at a time and narrow down the circuit that's causing the issue then go hunting for devices with asymmetrical start current draw on power-up. Most likely will be a switch mode supply on a PC, laptop, charger TV or other electronic device. Could even be a lighting driver or ballast but take your soldering iron with you and when you find it replace the MOV surge arrestors if possible or replace the entire power supply if you prefer.

 

[Farmelectrics]

Why so many power cuts

 

[steve1999uk]

Hi thanks for your quick replies it still trips when every circuit is disconnected and neutral bars and earth also disconnected .They live out in the sticks and do seem to have more than there dair share if power cuts .Have tried replcement rcd and still tripped can only use crabtree due to it being the strabreaker fitting . Is it common to these rccb's have seen on other forums ppl having same problem but no answers has really baffled me think answer might be to put freezer circuit on rcbo or swap entire conumer unit for a more upto date one ???

 

[steve1999uk]

Please help me anyone

 

[Richard Burns]

If you have an RCD that is not connected to anything on the outgoing terminals and is tripping when power is applied to it then it can only be a faulty RCD, even though you have changed it.
The RCD is only going to trip if there is an imbalance between the outgoing line and neutral currents, if there is nothing connected then there can be no current flow to be out of balance.
If there is anything still connected then that is where the fault must lie. If you have removed all circuits from the earth and neutral bars and have all the MCBs off then have you checked to see if there is a damaged bus bar tail that is nearly in contact with earth /neutral and the potential jump on switch on may be enough to bridge the gap.
If the MCBs are still on then there could still be a fault line to earth somewhere on a circuit.

 

[Marvo]

.....it still trips when every circuit is disconnected and neutral bars and earth also disconnected ..........Have tried replcement rcd and still tripped.........

Ah, slightly different ball game if it's tripping with nothing connected to the load side of it.

I could only think of harmonics from an external source as a possible cause which wouldn't be easy to test for. A long shot of it being 2 RCD's with the same fault or problem so maybe try another replacement but it's pretty unlikely.

Maybe RCBO's isn't such a bad option in this case. I'm not sure if it's a known issue with that particular RCD or not but if you're 100% certain you've tested all the final ccts thoroughly and it's far to travel it might even be worth discussing a CU upgrade with them.

 

[davesparks]

Have you checked that the board itself is ok? It might sound a bit far fetched but with the enclosed/inaccessible plug in busbar of those boards it may be possible that damp or corrosion in there may just be enough to cause occasional tripping?

 

[baldsparkies]

Had this once with a TT system.
The property was fed from a pole mounted overhead supply transformer.
The DNO installed an earth rod (not a twig) from the neutral terminal at the Henley/cutout within the property, and no it wasn't PME, still a TT system.
Anyway it cured the problem, no more nuisance tripping from the Rcd.

 

[Farmelectrics]

the op hasnt told us what earthing arrangement it is

 

[baldsparkies]

the op hasnt told us what earthing arrangement it is

Yer right Farm, he does say they live out in the sticks though so TT would be my guess.
Place yer bets gentleman please !!

 

[Leesparkykent]

Yer right Farm, he does say they live out in the sticks though so TT would be my guess.
Place yer bets gentleman please !!

ill have a pinky on it being TT Lol

 

[Farmelectrics]

I'll go each way

 

[DPG]

I'll go each way

I read that on a toilet door. Daz

 

[Dave OCD]

Did any manufacturer ever produce a 'front end' RCD that was configured to isolate in the event of mains failure- just as some RCD sockets are designed to do this- 'passive' or 'active' is the terminology ?

 

[steve1999uk]

Ello again everyone thanks for your valued and funny input just to let you know its got a PME no overhead cables they were remoced several years ago and underground cables installed in the village its a split load starbreaker board so I'm trialling rcbo's on thr non rcd side to see if they trip if not then thats the route i think I'll be going down

 

[Marvo]

We refer to them as an NVR RCD but I've never seen them on a domestic or commercial DB or CU. NVR = No Volt Release