Tripping RCD: Installing RCBOs...?

[shortshrift]

I've been plagued by intermittent RCD trips in the last few weeks - 12 to date, sometimes 4 in a day, sometimes nothing for 10 days, the irregularity making it impossible to identify the failing circuit by exclusion.

Clearly I'm going to have to get an electrician in, but if he can't rapidly identify a bad circuit/appliance/RCD (and maybe he won't see anything... it is intermittent), I'm thinking my next course is to have him swap out the RCDs for RCBOs, so (a) I get to identify the affected circuit, (b) in the interim the trips don't take down the freezer, fridge and heating controls if I'm out of the house.

I have a Proteus consumer unit with 8 x 632B1 32A Type B MCBs and a 63/2/30T RCD. Is it possible to simply swap the MCBs for RCBOs (Proteus 326MBRSP has similar characteristics)? And then I guess I would need to replace the existing RCD with a time-delayed RCD since the RCBOs are single pole and don't protect against Neutral-Earth faults?

And are other brands (e.g. Wylex) compatible with the Proteus consumer unit...?

Thanks in advance!

 

[JohnD]

If you are going to all that trouble and expense you might consider throwing away the Proteus and buying something better.

It is notifiable work.

Why do you think you need a time-delayed RCD as well?

If you get a N-E fault it will trip both the RCBO and the RCD since the RCBO will not isolate the N

 

[phatboy]

I have RCBO's, and they definitely trip on N-E faults

JohnD - he said he was getting an electrician to do the remedial work, so no notification required.

 

[JohnD]

I have RCBO's, and they definitely trip on N-E faults .

Yes, they will trip, but they will not isolate the N-E fault, so his proposed RCD will trip as well.

If you get a N-E fault it will trip both the RCBO and the RCD since the RCBO will not isolate the N

I suggested he change the CU. Having an electrician in does not make notifiable work become non-notifiable

 

[EFLImpudence]

And then I guess I would need to replace the existing RCD with a time-delayed RCD

No. Just remove it.

The RCBOs are replacing the RCCB.

If the RCCB was also the Main Switch you will need a Main Switch.

 

[shortshrift]

Thanks for the replies.

My thinking on the time-delayed RCD is that while the RCBOs will trip on N-E faults, single pole RCBOs will do nothing to isolate the fault: they'll trip, but the N-E leakage will continue all the same.

So a double-pole RCD is additionally needed to gain full protection. And the purpose of the time delay is so that on L-E faults, the fault is interrupted by the RCBO before the RCD trips and I don't lose the whole house.

I'm not overkeen to go down the RCBO route, but with an intermittent RCD trip (sometimes 4 times a day, sometimes not for 10 days) I'm having difficulty establishing any pattern or solving it by elimination, and I've got a suspicion that when I call an electrician he'll test all the circuits and tell me they're all fine, so what to do then...?

I originally thought it was the Central Heating pump struggling. Seemed to be a smell of hot electronics around that area, and after bleeding and repressurizing the system I didn't get any more trips for a while. And then I did. Maybe the pump/insulation has been damaged by overheating. Or maybe it was a red herring.

Could also be water ingress somewhere in the house, as perhaps the trips have been more frequent on wet days, but the correlation is not 100% and there are no obvious signs of damp.

Or maybe a faulty appliance. My first thoughts were the fridge and freezer, but I've had the RCD trip with both those turned off.

I watched yesterday a YouTube video where a guy demonstrates a perfectly healthy PS3 leaking 2mA+ to Earth (presumably a result of capacitance in the PSU)... if this is typical then a house with a lot of electronics isn't going to need much of a nudge to reach the 18mA-ish threshold of an RCD. In that respect, anyway, I would benefit from RCBOs, since these leakage currents wouldn't be summed across all circuits.

Ho hum.

 

[Chri5]

If the ch pump is on a timer, and the trips match the on setting there's a bit of a clue.

A split board would allow you to know its one of 50% of circuits

It's more likely a socket circuit, lights tend not to cause problems unless they are outside or subject to damp moist air.

Elimination, drop a circuit for 12 hours and see. Things like fridges can be put on a temporary lead to another circuit.

Kettle, water heating, irons, leaky fridges, freezers, older electric cooking appliances could cause. That aside maybe the rcd is knackered, some do fail because they start tripping well below the 30mA .

You might be able to mod the board and make a direct way, then rcbo some circuits and rcd with mcb others.

 

[shortshrift]

Chri5, thanks. All good stuff!

Unfortunately I have had 10 days between trips (which led me to think I'd fixed it), and then...

Given which, it's a very slow business to exhaustively exclusion test since you only get a data point in the event of a trip and the test circuit has to remain excluded for all that time.

I've been outside and eyeballed the exterior lights suspiciously (they remained impassive under my gaze...). They're all off at their respective switches, but that doesn't preclude a N-E leak from moisture if the switches are single pole.

Regarding the CH pump: yup, if the RCD trips coincided with the heating timers that would be a big clue, wouldn't it? But the pump runs okay plenty of the time. Doesn't mean it isn't occasionally spiking or that the insulation isn't marginal. And also in my setup the boiler fires even outside timer periods - CH/HW simply open motorized valves; even with both valves closed the boiler is still maintaining a small closed loop of water at the set temperature and firing periodically.

I've just opened up the boiler and turned it off (can't find an external switch... surely there should be one). See how that goes. At least if the RCD does trip now I can rule the boiler out and look elsewhere.

 

[JohnD]

I've been outside and eyeballed the exterior lights suspiciously

open them up and look for traces of water inside enclosures, switches, junction boxes.

also look in the loft for signs of leaks.

look behind fridges for melt water spilling

it's usually water.

 

[shortshrift]

JohnD, Thanks.

"it's usually water." I bet.

I still have some money on the CH pump because it did smell overheated first time the RCD went and because the tripping did disappear for some while after I bled and repressurized the system.

Two other thoughts that occur: (1) With damp in a light fitting, would it always be intermittent trips, never an unresettable hard trip (I'm up to 13 now, over about 3 weeks)? I suppose this is possible if noise from some other appliance is briefly taking the total leakage past the trip point, but if so I'm surprised the damp produces such a constant, consistent effect, never a hard trip. (2) It would have to be a N-E leak, as the exterior lights are all off at their switches. Since Neutral and Earth are usually at similar potentials, there would need to be a good conduction path for 30mA, so how common a problem are these?

Have managed to rule out fridge and freezer (got a trip with these off), and loft seemed completely watertight in the parts I could access. Guess I'll have to get a ladder and open up the exterior lights. Deep joy.

 

[JohnD]

You might like to try an RCD adaptor, as used for lawn mowers, and plug suspect appliances into that.

When I used to test, I found the adaptors tripped faster than the RCD in a CU ( I assume because they have lighter contacts so less inertia), but more often than not they would both trip. There were only 5 or 10 milliseconds difference.

 

[martinxxxxxx]

Having an electrician in does not make notifiable work become non-notifiable

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Location: Argyll

 

[martinxxxxxx]

From what you have said I would disconnect the heating system, unless you still need it on..

See if that does the trick.

Also an insulation test meter from fleabay might shorten your quest. Other than that see if you can buy an hour of a decent electricians time

 

[JohnD]

Location: Argyll

building warrant, then?

 

[phatboy]

If he is going to employ an electrician, he shouldn't need to worry about notification, the electrician should deal with this - was my point