RCD nuisance tripping.

Jeepers_Creepers

Hi all.

This has been happening for around a month, always in the morning. Occurred a few times before Chrimbo, but fortunately behaved itself on the day, and for most of the time since then. It's now started happening again, twice in the past few days.

At around 7.30-8.00, the RCD trips and everything goes off. Sometimes - usually - I can reset it right away and it stays on, but occasionally it trips again very quickly, which I thought would at least allow me to start isolating circuits one at a time to see if I could ID the cause. Nah. It's too inconsistent - sometimes I can turn off a circuit (starting with the most likely contenders such as outside lights, the cooker, etc) and the RCD stays on, but then when I re-engage the 'tested' circuit, the RCD stays on. So completely indecisive.

It ain't the CH 'cos that comes on well before, and turning off the boiler doesn't make any difference. It ain't the garage as that's on its own consumer unit with RCD since I had PV panels fitted and then had some nuisance tripping from that - its own CU sorted that.

There is nothing I can tie it to - nothing it being activated at the relevant time. Lights are either on or off - none being activated to make it trip. Ditto kettle - this can be used before or after, but it also doesn't cause the trip during use. Radio has been on for an hour. No TVs are being used.

I guess it's time to get a sparky out to test each circuit. A theory I have - tho' I don't know if it's nuts - is that it isn't any single circuit or item causing this, but an accumulation of small leakages/imbalances which are hovering somewhere below the 30mA trip point, but then in the morning the electricity board are perhaps turning on more power to cope with the morning rush of kettles and toasters and stuff - this might be causing a voltage a bit higher than usual, which would then cause a similar blip in the current - perhaps enough to trip? Nuts idea?

Any other thoughts? Cheers.

FreeBear

Jeepers_Creepers said: Any other thoughts?

The RCD developing a fault ?

They don't last for ever (I've had to replace mine last year).

Jeepers_Creepers

Good point - I did wonder. I recall I replaced it before, well over a decade ago.

That seems like a good move before getting the pros in.

Cheers.

grumbler

I had a laptop power supply that kept tripping my RCD.

Sandtree

RCD itself could have a fault but the fact it trips every day at 7:30-8am suggests that its something that kicks in at the time thats causing it... I'd expect a fault with the trip switch itself to have no pattern.

Moss5

Consider changing to RCBOs in the consumer unit.
As you say, a cumulation of petty faults can exceed 30mA. Better to give each circuit the 'right' to it's own 30mA. I have an LED indicator for each circuit to make me aware that one circuit has dropped-out.
If you use a toaster, put that on the suspect list. May be more crumbs in there than you would like to own-up to.

Jeepers_Creepers

grumbler said:

I had a laptop power supply that kept tripping my RCD.

Blimey! Pretty sure not the case here, tho'. How did you work that out?!

Jeepers_Creepers

Sandtree said:

RCD itself could have a fault but the fact it trips every day at 7:30-8am suggests that its something that kicks in at the time thats causing it... I'd expect a fault with the trip switch itself to have no pattern.

Yes, there's something amiss at that time, but I really cannot pin it down to anything in the house.

Jeepers_Creepers

Moss5 said:

Consider changing to RCBOs in the consumer unit.
As you say, a cumulation of petty faults can exceed 30mA. Better to give each circuit the 'right' to it's own 30mA. I have an LED indicator for each circuit to make me aware that one circuit has dropped-out.
If you use a toaster, put that on the suspect list. May be more crumbs in there than you would like to own-up to.

Gulp - I have 17 MCBs :-(  

If I were to replace, say, the socket circuits with RCBOs, would it be ok to keep the main RCD in place or would that need removing?

Yes, toaster, but used rarely, and not at that time.

theoretica

Could it be something external happening at that time?  A small surge on the line/a neighbour's device affecting the neutral.  They shouldn't trip your circuit if everything is working properly, but if yours isn't quite right there could be a minor external trigger.

shinytop

Are you on economy7?  Ours switches over at 7:39 precisely every morning.  We can hear it because we have a 3 phase supply with a contactor switch.  Might be irrelevant to you but it is something that happens at the same time every day and might cause the blip you're thinking of.