Wylex RCBO Intermittent Tripping

[uksparks]

Hi,

I went to see a house today where their plug circuit on a 32A Wylex Type A RCBO keeps intermittently tripping each day.

Its a TNC-S, Wylex board with 6 protected by RCD and three on RCBO's. Board was changed 3 years ago.

The RCBO that's on the plug circuit keeps intermittently tripping. I checked all connections etc and nothing obviously wrong at the board.

What I have done is Ramp tested the RCBO to see what its tripping at and its going out at 15mA which is low, but I understand on the Wylex RCBO's this is not too uncommon. I said it could be an accumulation of leakages causing this. I put my ELCM round the tails which measured 13.7mA and round the main earth that was 21mA.

There a couple of outside sockets protected by RCD spurs, bit of SWA to the shed with another RCD ( in the shed there's a fridge and a freezer). The RCD spurs, ive left tripped for a moment to help eliminate the outside sockets.

I have checked all appliances for earth leakage when operating, I have a small extension with the earth wire exposed that I check with, all appliances were under 0.5mA each so nothing to bad there. Even disconnected and checked the boiler.

I did an RCD test on it, which was fine, nicely within limits, nothing abnormal on both 0 and 180, good Zs etc...

I am not sure why the person who changed the board used a Type A RCBO, actually all three of the RCBO's are Type A. I swapped the shower RCBO and the plug circuit RCBO round as they were both the same size (32A) and the shower ramped out at 18mA which again I think is a little on the low side.

I said to the bloke, without sounding useless, and spending more time looking at all accessories etc and carrying out more tests as only did basic bits today, I said it might be worth changing or try changing the plug circuit RCBO out for a new one Type AC and hope its got a better threshold.

Am I correct in thinking the Type A has something to do with being able to withstand more DC back voltages or something? Seems to ring a bell, ill be honest, I've never used a Type A so little knowledge of them.

I said try unplugging one appliance at a time and leaving it 24 hours before moving on to the next to see if you can pin it down at all. You see, it does it at like 6:30am, which instantly made me think immersion (which they have not got) or a boiler maybe, but the boiler seems to be ok even when on, so maybe would a valve cause it?

So really, why and when would you use a Type A RCD in a domestic environment and any pointers? I am normally quite good at pinning down these problems, but all the obvious appliances seem to be. I am guessing its going to be a Class 1 appliance but not too sure now. I feel the bloke who changed the board (NICEIC AC), made a nice job, but had a problem when he did which is why he went Type A on the RCBOs?

Any points much appreciated.

 

[alanl]

Hi,

I went to see a house today where their plug circuit on a 32A Wylex Type A RCBO keeps intermittently tripping each day..

I'm presuming that is an A type RCD, rather than the overcurrent part being 'A'?

Presumably you have done insulation tests on the circuit?
Is it the RCD, or the overcurrent that is tripping?
Only once a day points to an appliance or timer etc causing the tripping if the RCD, or possibly everything comes on and overcurrent protection causes it?
You are not clear what is on the circuit, you say some RCD spurs - what is that, a RCD fused spur being fed by a RCBO?
Anyway, if dead insulation tests are good, it is more than likely something connected to the circuit that is causing the fault. Get the info on when it is tripping, and narrow the fault down. It has been awfully wet recently, I'd be looking at anywhere that water could have got into an appliance.

 

[Darkwood]

Ramp testing will not show what the trip level of the device is unless the circuit is off load and insulation tests confirm integrity of the cable, if you have 6mA background leakage already and the ramp trips at 15mA then its effectively operated at 21mA.

You need to liaise with customer to establish exactly what is plugged in when it trips and log times and dates d see if any links can be establised, also note the weather too is it windy or raining - maybe an external circuit tapped off the ring is effected by the weather.

And yes as alanL points out the A is possible the Ampage symbol mcb's / rcbo's are not made in type A specifically for the reason A is already used for Ampage symbol.

 

[HandySparks]

I think that type A RCBOs are a fairly standard offering nowadays, i.e. sensitive to a pulsating DC component, due to increasing use of semiconductors in equipment which can cause this type of current draw. I checked my own (Crabtree) CU which I installed a couple of years ago and all the RCBOs are type A.

You say that you've clamped the tails and found 13.7mA of differential current. Do you have the figure for the particular circuit in question? If anywhere around 10mA or above, then you need to track down the reason. Also, as above, what were your IR readings for the circuit? (L+N to E would do).

 

[uksparks]

Sorry was eating dinner, I was only there 30 mins as had to go but am going back for further investigation.

the circuit IR was >250 lives to earth, I didn't do a full IR test as didn't want to kill any unsuspecting appliance.

the tripping is any random time in the day, might only happen once, most its happened is 5 times in a day. It a strange one, when I measured the ramp, I did it with all circuits off apart from the plug circuit but with all readily obvious appliances switched off, I also redid the ramp on the shower circuit after swapping the RCD and it was tripping out at 15mA with the shower off etc.

 

[uksparks]

forgot to add, my IR test lives to earth was >250M, the EIC that I saw, said each above >250 not limitation too, so on that basis if that's accurate, chances are the IR is possibly ok, but things do change.

I did say to the bloke, it is now cold and wet and has only started this last week, so could be damp or wet in a box where the SWA connects, or the outside socket etc..

I need to go back to have a proper look, unfortunately I was meant to be there earlier but the van got a blooming flat tyre so had to sort that first so didn't leave me much time.

 

[guest119]

Central heating pump?

Boydy

 

[uksparks]

I am still thinking along the lines of something to do with the heating, just because its random which kind of fits with fluctuating temperatures etc. I don't really do much on the heating side, but am guessing a valve or something like that that's powered that does something when the temp drops or whatever it needs to do.

Like I say, I'm usually pretty good at sorting these problems without any input from others, but this one seems to have be wondering as from what I can tell on the surface, things 'appear' to be ok. So its got to be something that's switching in and out and random times.

 

[Octopus]

Are you saying there are RCD's on the same circuit in the shed?

 

[uksparks]

Yes, there's a small cu in the shed, for plugs and lights, it's got the fridge Nd freezer connected, it's got a normal 30mA RCD in there, so no discrimination between that and the house, plus there's two power breaker rcd spurs in the house feeding outside sockets, all I can assume is these and the shed cu probably existed prior to the new board that got fitted a couple of years ago.

The shed doesn't trip out, it's only the one in the house, I need to have. Better look to be honest. As said above, have tested all appliances and am happy with them with them on and functioning so to speak. There's got to be something lurking in a corner.

 

[Octopus]

Yes, there's a small cu in the shed, for plugs and lights, it's got the fridge Nd freezer connected, it's got a normal 30mA RCD in there, so no discrimination between that and the house, plus there's two power breaker rcd spurs in the house feeding outside sockets, all I can assume is these and the shed cu probably existed prior to the new board that got fitted a couple of years ago.

The shed doesn't trip out, it's only the one in the house, I need to have. Better look to be honest. As said above, have tested all appliances and am happy with them with them on and functioning so to speak. There's got to be something lurking in a corner.

And all we can assume is that the sparky that did the change didn't use their eyes or these would no longer be in place!

 

[uksparks]

Yeah well if I had done it I would have taken them out too. To be honest the board change was not that tidy, lots of exposed copper, jotted wires and the like, I'll take a pic when I go back, plus they have cut the tails on the rcbos to the point you cannot even move them one space, what a plonker eh!

 

[uksparks]

The customer called me this evening to say that since I swapped his breakers over and the slightly less sensitive rcbo is now on the plug circuit, he has had no tripping and everything is working ok. So by swapping his rcbo on the plug circuit that was tripping at 15mA with the on that was on the shower that was tripping at 18mA it seems have fixed it, so it must just be n accumulation of earth leakage causing it. I didn't charge him as I didn't know if it would work, he said send him a bill but I said just tell people I fixed your problem that will do.

I said there's little point in replacement it if that's resolved it, at least it's stopped tripping 3,4,5 times a day anyway.

 

[PEG]

Hope it resolves the issue but 3mA is not a lot of insurance against another call-out...

 

[uksparks]

I know, well it might have only been just tipping the other over edge, I'll change it for a new one if it happens again, at least it's fixed it for now.