Help on strange RCD trip issues

[EwanMcD]

Hello all,

Do any of you know what could cause a 15-20 minute delay on being able to restore power after an RCD trip?

I’ll explain the problem:
About once every four months we have an RCD trip, where the problem is the kitchen/garage electrical circuit.

If I try to flick the power to the kitchen/garage back on within the consumer unit, it immediately trips the RCD again.

To isolate the problem/fault find, I try turning off each appliance within that ring, no appliances are at fault, with everything unplugged, the RCD still trips immediately when trying to restore power to the ring/circuit.

This is the strange bit, after about 5-10 mins, when trying to restore power by switching the kitchen/garage ring on at the consumer unit, the RCD doesn’t trip until about 3 seconds after applying power.

After another 20 mins or so, applying power at the consumer unit doesn’t trip the RCD. All appliances can be plugged back in and it’s usually 3-4 months before we see the problem again.

There have been logical reasons for the initial trip, we have fridge/freezer/dishwasher in the kitchen and Fridge/freezer/chest freezer in the garage. Too much current could easily explain why it trips in the first place.

What I don’t understand is why (with everything unplugged), you have to wait 20-30 mins before applying power back to the ring is successful?

Has anyone experienced anything like this?

 

[winston1]

There have been logical reasons for the initial trip, we have fridge/freezer/dishwasher in the kitchen and Fridge/freezer/chest freezer in the garage. Too much current could easily explain why it trips in the first place.

That is rubbish. RCDs do NOT trip on over current. They trip due to an unbalance between line and neutral, usually due to a leakage to earth.

 

[EFLImpudence]

The first thing to clear up, then, is -

is it an RCD (RCDs have test buttons) that trips or an MCB?

 

[EFLImpudence]

 

[ericmark]

I did look at this, and I considered what can delay being able to reset, there have been some electronic RCD's which are designed not to trip with spikes, but I have never found a RCD that when the loads are removed will not reset until a time has lapsed.

What I don’t understand is why (with everything unplugged), you have to wait 20-30 mins before applying power back to the ring is successful?

I also don't understand that, if the freezer was still plugged in then maybe a fault on the auto defrost, but he clearly says with everything unplugged, so I would be looking for some thing missed.

One RCD for kitchen and garage seems unusual, possible a RCBO but with twin RCD's in a CU seems an odd split?

I have had problems with my caravan with RCD tripping and then next day could reset, I would assume water ingress some where, never did find out why, so suppose could be same as you describe, with mine there was without question a real leakage fault as took out both caravan and caravan site RCD's but like with you fault vanished and when I got home and used insulation tester no fault found.

So would look at garage, and consider weather, was wind blowing in set direction? could some thing get wet then dry out.

 

[EwanMcD]

Hello, cheers for coming back to me...
The RCD trips.

If I turn off the MCB for the ring mains in the kitchen, the RCD will switch on no problem.

When the kitchen ring mains MCB is switched back on, the RCD immediately trips.

If every appliance associated with the kitchen MCB is turned off and the MCB is turned on, the RCD still immediately trips.

After waiting for 5 minutes and turning on the kitchen MCB, the RCD still trips but there’s a few seconds of delay before the RCD trips.

After waiting for 20 minutes and turning on the kitchen MCB, the RCD doesn’t trip.

Turn all appliances on, RCD doesn’t trip, turn kitchen MCB off and on, RCD doesn’t trip.

So no matter what is done at the moment, switching on/off MCB’s, running all kitchen appliances etc, everything is running as normal but this fault appears a few times per year where leaving the MCB off for 20 mins resolves it.

Just looking for any ideas as I want to get to the bottom of it.

 

[EFLImpudence]

If I turn off the MCB for the ring mains in the kitchen, the RCD will switch on no problem.
When the kitchen ring mains MCB is switched back on, the RCD immediately trips.

That would indicate a Line(Live) to Earth fault - MCB only disconnects the Line(Live).

If every appliance associated with the kitchen MCB is turned off and the MCB is turned on, the RCD still immediately trips.

Do you mean just switched off at their controls or at a wall switch?

After waiting for 5 minutes and turning on the kitchen MCB, the RCD still trips but there’s a few seconds of delay before the RCD trips.
After waiting for 20 minutes and turning on the kitchen MCB, the RCD doesn’t trip.
Turn all appliances on, RCD doesn’t trip, turn kitchen MCB off and on, RCD doesn’t trip.

As Eric said re: the weather, that does look like some drying or cooling down.

So no matter what is done at the moment, switching on/off MCB’s, running all kitchen appliances etc, everything is running as normal but this fault appears a few times per year where leaving the MCB off for 20 mins resolves it.
Just looking for any ideas as I want to get to the bottom of it.

Every four months is going to be difficult to pinpoint the fault.

 

[ericmark]

OK seems there is a real fault, i.e. RCD doing what it should do.

Water is most likely cause, possibly some sort of syphon? Water builds up then it reaches a point where some thing releases it, then slowly builds up again and it releases it onto some thing which can short out.

It could be a membrane that slowly stretches then releases. In my kitchen we had a leak, it was caused by faulty tile when building extension, but extension was up some 10 years before it started to come into kitchen, it did not matter what we did, it always seemed to cure the leak then it would start again, the water was building up being absorbed by the fibre glass and we blamed build up of moss on the roof, until one builder saw the faulty tile.

In our case it was not getting the light or any other electric item wet, so was not tripping electric, but water can build up then release, and it would seem that is most likely cause.

 

[jj4091]

I think your best chance of finding the fault is to get an electrician with an insulation tester to check out the affected circuit. A higher voltage applied to the cables may well make the intermittent fault show up.

 

[ericmark]

I think your best chance of finding the fault is to get an electrician with an insulation tester to check out the affected circuit. A higher voltage applied to the cables may well make the intermittent fault show up.

Had it not been for my caravan I would agree, however even on the 1000 volt range I could find no fault. An insulation tester new from internet costs around £35 clearly no calibration certificate at that price. But compared with my Megga it showed same results so clearly good enough for DIY.

However if caused by water ingress then you want to cure that ingress, items like air conditioning units collect condensation and once it reaches a set point pumps it out, I know from experience one clip missing and the waste pipe can come off and it was pumped onto suspended ceiling, no one realised until the ceiling fell down.

Trying to work out where water may enter is not something we can do on a forum, and getting an electrician to attend before fault goes again may also be a problem.

My garage is fed with a fused connection unit, I would say if that's the case, remove the fuse next time it happens.

 

[crystal ball]

Might be worth taking a few socket fronts off, last year I found a slug in a back box which was causing trip problems

 

[donrkebab]

Get an electrician to test the rcd, seems faulty to me.

 

[baldykev]

You say its the kitchen/garage circuit ,you don't have any exterior lights wired to that circuit ? like in or on the garage ect (could be water ingress)

 

[bernardgreen]

A fridge or freezer that "auto defrosts" collects the water from the melted frost in a dish fitted to the top of the compressor. If there is too much frost then there is more water than the dish can hold and overflow from the dish. In some models this excess water gets to the terminals of the compressor and earth leakage occurs.

The keat from the compressor evaporates the water ( in theory but not always in practise )