RCD nuisance tripping.

Jeepers_Creepers

Thanks Ris - that's useful to know.

Took some voltage readings to see if there's any potential mileage in 'that' theory.

At 1am last night it read 246.9V. That's a touch high, isn't it? The RCD didn't trip this morn (even tho' it was very blustery and quite heavy rain lashing - another potential correlation I'm keeping an eye on) but I took a series of readings before and after the usual trippin' times. 7.40 - 243.3V (so less than last night), 7.55 - 244.1V and 9.10 - 242.7V

So all pretty consistent. I'll keep my meter ready for action the next time it 'blows', see if there's any obvious change to the above.

DiddyDavies

Jeepers_Creepers said:

Thanks Ris - that's useful to know.

At 1am last night it read 246.9V. That's a touch high, isn't it? 

The voltage can actually go as high as 253V and still be within spec.
The voltage in the UK has been set at a nominal voltage of 230V with an allowable tolerance of -6% and +10% so in theory it could be anywhere between 216.2V and 253V.

AskAsk

i had an issue a few months ago where the MCB for the downstairs would go off.  you could reset the MCB and it would work again but after a few go it refused to be reset or if it did, it would only stay for a couple of hours before going off again.  then it became about 30 minutes before it went off again.

i tested every circuit and appliance and nothing tripped the MCB.  it just seem to trip all by itself at random.

luckily i had already booked the electrician to come round and replace the consumer unit, which was old.  so when he came i asked him to look at the issue as part of the work and he said it was the downstairs sockets causing the intermittent tripping as the downstairs circuit included the kitchen, which did not have its own MCB!  he said he thought it was a problem with the cables or a junction box under the floor.  as the floors were laminate wooden floors, he advised the best option was to rewire the downstairs sockets so we didn't have to lift the floors to work out where the fault was.

i decided to do that and it resolved the issue.

Jeepers_Creepers

Cheers, Diddy - well within parameters, then.

Thanks AskAsk, but that's a different issue in that an actual MCB was being tripped, suggesting a short-circuit... Gulp. Pleased you had it sorted.

Petriix

It does seem coincidentally close to the time when the PV inverter will have been kicking in; especially if it was causing issues before.

Jeepers_Creepers

That's a good point, thank you, and one I did consider. It's still very dark when this tripping happens, whereas the PV system caused issues as it tried to 'connect' to the grid, and that only happened when it had detected a generated voltage - ie. the sun was coming up. (I assume - it's not on a timer, is it?!)

The PV system/garage is now on its own CU with RCD so is the only thing still running when everything else has gorn orf. Could it still cause an RCD trip on the main board, I wonder?

I think I'll proceed with replacing the main RCD with a non-RCD type switch, and then swap half the MCBs for RCBOs to start with - all the socket circuits and some of the other rmost likely - or risky - other circuits, like outside lights. This would be a better setup anyway, so wouldn't be a waste.

Ectophile

Another thing that can trip an RCD, though in theory it shouldn't, is a short current surge.  Fridges and freezers are culprits for that.  On their own, they are unlikely to cause a trip, but when combined with a background level of leakage, they might.

AskAsk

i would be interested to know what is the cause when you finally get this resolved.

fenwick458

Jeepers_Creepers said:

I think I'll proceed with replacing the main RCD with a non-RCD type switch, and then swap half the MCBs for RCBOs to start with - all the socket circuits and some of the other rmost likely - or risky - other circuits, like outside lights. This would be a better setup anyway, so wouldn't be a waste.

that sounds like half of the circuits will end up with no RCD protection?
17 circuits is a lot, if that were my house I wouldn't bother with 17 RCBO's. I'd have all the sockets and lighting circuits on RCBO's, and the rest of the circuits spread across 2 RCD's.
but It does depend on what type of consumer unit you have, and the price and availability of parts for it

Jeepers_Creepers

fenwick458 said:

Jeepers_Creepers said:

I think I'll proceed with replacing the main RCD with a non-RCD type switch, and then swap half the MCBs for RCBOs to start with - all the socket circuits and some of the other rmost likely - or risky - other circuits, like outside lights. This would be a better setup anyway, so wouldn't be a waste.

that sounds like half of the circuits will end up with no RCD protection?
17 circuits is a lot, if that were my house I wouldn't bother with 17 RCBO's. I'd have all the sockets and lighting circuits on RCBO's, and the rest of the circuits spread across 2 RCD's.
but It does depend on what type of consumer unit you have, and the price and availability of parts for it

Yes, 17 circuits is nuts, but it's what I inherited - it's in a 20-space MEM 2000. I did add to the excessiveness myself since then by having a sole 20A MCB for the 4 sockets in the room I'm in now, converted from the attached garage, and possibly even a single one for just the lighting in here - 2 wall lights... Then there's a separate MCB for the doorbell (don't ask... Ok, it was because it used to supply an ancient 'Bell' porcelain & Bakelite trannie, so I kept it when I fitted a modern replacement), separate S and L circuits for the upstairs when it was converted, ditto for the new extension - you get the idea :-)    

I'm thinking there's some circuits that will just not require the added protection of an RCD - the lights in this room, the doorbell, for example - so will instead focus on the important ones first and hopefully ultimately do pretty much all of them.

First I need to track down RCBOs for a MEM 2000... :-(