RCD Trips after two minutes ?

[Dave1982]

Hi all.

Can anyone tell me why an RCD would take more than 2 minutes to trip after the main supply circuit has been energised.

Will not reset immediately afterwards but will reset after 3 to 5 minutes of isolating the circuit.

This is with no loads connected. that is all MCB's switched off.

My supply is from a SWA cable connected into a fused switch incorporating a BS3036 60 Amp fuse. The cable run is approx 12mtrs from the meter and cut-out dissapearing into the wall cavity and reappearing upstars of a domestic property converted to an appartment.

Any expert help would be gatefully appreciated.

 

[Octopus]

Hum, have you done any IR tests?

 

[Richard]

Do you have the means to test the RCD?

 

[Dave1982]

I will be back tomorrow with my tester and will be able to do some tests.

What is stumping me is the delay in tripping. which would or could be explained if the RCD were based on thermal aspect of overload and not imballance of current. any thoughts on that ?

 

[Dave1982]

I suspect there may bedamage to the SWA cable.?

 

[tony mc]

It would be a guessing game.

You need to carry out all the dead tests tehn the live along with RCD tests in case its duff.

It wont be on the SWA IMO as this is only suppling the power to the RCD it does its job by protecting the load side for any earth imbalances.

It will be on your load side neutral to earth fault as you are only switching of the line conductors with the MCB's if it is a cct

Try taking out all of the neutrals and replace them one at a time until you get your tester.

 

[Dave1982]

Thanks Tony for that advice will do as you advised. Why the delay in tripping? how can that be explained?

 

[tony mc]

Earth leakage could be anything water in fitting screw nipping cable in fitting you will have to IR the ccts to find the fault.

 

[nickblake]

I would carry out all the tests again IR especially make sure all is ok with the circuits andensure all appliances are un plugged

 

[Dave1982]

Sorry to be a nuisance Tony. I'm getting abit confused here. You say the rcd works on an imballance of current in the Line and neutral wires. I'm clear with that.

If there is no current flowing supplied to the line conductors there is no current in the neutral conductors iether. so no imballance should occure if there is a potential route to earth from a short between earth and neutral. Is that right? The problem also occured when I removed all line conductors from each MCB not just switched off. Its been a long day so I may be talking giberish.

 

[Kamikaze]

I would check the connections of the wires. I sounds like the earth and neutral are reversed on one of the circuits.

 

[Dave1982]

Anybody else comment on my last post please

 

[RogertheBodger]

All your Neutrals are connected together in the cu, there is always a bit of current N-E, all it takes is 30Ma.

 

[bugsy]

Experianced the same problem on a job last year only it took between 5 and fifteen mins to trip rcd, turned out to be water ingress a JB feeding spike in the garden causing low I/R on earth and neutral

 

[pushrod]

I would test your rcd and also ramp test it - you could well have a dodgy rcd. If you can't get it to hold while testing try putting one that you are confident is working or another new one in. Rule that problem out before spending a lot of time elsewhere imo.