RCD nuisance tripping

[rad1o]

We have had a split load C/U installed about 5 years ago. We have always had some tripping often when electric motors were started like lawn mower, drills, grinder. We had the unit tested and the electrician could not isolate the fault, but found that there was continuity between the lights and a socket ring. All tests were fine.
I have been reading about RCD tripping and have read the advice to change the RCD to an RCBO. This seems a more sensitive device than a RCD. Would this not cause more tripping than we already have?

 

[Marvo]

You would probably require several RCBO's to replace a single RCD. RCBO's aren't necessarily more sensitive but if the RCBO trips you only lose power on the one circuit whereas an RCDtrip will cause power loss on several circuits.

 

[Sharpend]

Interestingly what did the electrician do about the continuity between sockets and light circuits?
An rcbo is no more sensitive than an rcd, it is basically an individual rcd device for a single circuit.

Personally I think a bit more testing if your current install, did your spark carry out an earth leakage test?

 

[Octopus]

We have had a split load C/U installed about 5 years ago. We have always had some tripping often when electric motors were started like lawn mower, drills, grinder. We had the unit tested and the electrician could not isolate the fault, but found that there was continuity between the lights and a socket ring. All tests were fine.
I have been reading about RCD tripping and have read the advice to change the RCD to an RCBO. This seems a more sensitive device than a RCD. Would this not cause more tripping than we already have?

Not sure those 2 facts stand. Did you get give the test results?

I think you should seek a 2nd opinion.

 

[rad1o]

We needed something else doing and had an electrician in and while he was here I asked whether he could just spend a little time to look at this tripping problem. I was watching over his shoulder hoping it could also help me understand the problem.
He tested insulation resistance, ramp, and had almost every wire in the fuseboard off and commented that the socket ring is not a ring but someone has branched off the ring. He said there was continuity between the lights and the sockets and it was not from within the fuseboard, it could be in a junction box in the floors or cables within a bunch of cables lying together if I got him right.
Now my thought was that I could put the MCB for the socket ring from the RCD protected side onto the unprotected side but stick it onto its own RCBO, which I understand is a MCB with RCD function in one...... So if anything trips its only this and not the whole RCD side.

 

[tony mc]

I take it that you are going to do the work yourself ! IMHO you need this looked at again as once you place the RCBO on the FRC if it is connected to the lights then the RCBO will not hold and you will be scratching your head. How can the electrician say ALL TESTS WERE FINE after telling you that a dangerous fault is present !

 

[telectrix]

We needed something else doing and had an electrician in and while he was here I asked whether he could just spend a little time to look at this tripping problem. I was watching over his shoulder hoping it could also help me understand the problem.
He tested insulation resistance, ramp, and had almost every wire in the fuseboard off and commented that the socket ring is not a ring but someone has branched off the ring. He said there was continuity between the lights and the sockets and it was not from within the fuseboard, it could be in a junction box in the floors or cables within a bunch of cables lying together if I got him right.
Now my thought was that I could put the MCB for the socket ring from the RCD protected side onto the unprotected side but stick it onto its own RCBO, which I understand is a MCB with RCD function in one...... So if anything trips its only this and not the whole RCD side.

that would be an idea, but you need to sort out the underlying problem first. no use treating the symptoms. you have to treat the cause. it seems like there are 2 problems. first the lack of end/end on the ring, and second, the link between the ring and the lights. probably a bit of DIY bodging under floorboards. if you ( or your sparks, preferably) can identify a socket that looks newer than the rest, or wall lights, that is a pointer as to where the problem lies.

 

[rad1o]

I do not know whether I would want to go into the fuse board myself. I have put extra sockets next to existing ones and changed light switches.
The problem with the house is that we bought the house from the 1930ies with an extension built by the previous owners in the 80ies and most of the wiring is in ceilings / floors.
If I can cure part of the symptoms I would sigh with relief.
I do not understand why not every MCB in a fuseboard is an RCBO so that they can trip individually just going by what I have read. Ok.,It might be overkill in some houses...

 

[telectrix]

RCBOs cost more, that's why.

 

[oldtimer]

Seems to me the consumer unit has been put on the back of maybe an old and creaking installation. You also mention mower,grinder,drill so can I ask what is common to all 3 ie an extension lead perchance ?

Sounds like the electrician could not pin down the fault because it was not their when he visited in other words an external influance so check your leads and hopefully there is not a lot of tape joints due to the lead getting run over by the mower

 

[plugsandsparks]

The current regulations have been interpreted as requiring a minimum of 2 RCDs which typically would cover 10 circuits. Increasingly this is not good enough to avoid nuisance trips and enable speedy diagnosis of a fault. RCBOs cost between 5 and 10 times the cost of a MCB

Assuming appliances is at fault, good candidates are: Steam iron, toaster, oven, dishwasher.
Any wiring or fittings that go outside are potentials.

You need an electrician with the right equipment to measure leakage whilst appliances and other loads are applied and take it from there. Its unlikely that the fault would not present itself in some form even if a trip does not occur at that time.

 

[rad1o]

We can trigger the trip if we "rev" the electric appliance, i.e. start repeatedly. We can also trip the socket ring on the RCD side with a light switch being flicked on and off at speed with the light ring sitting on the non RCD side. Sometimes the RCD does NOT trip with almost everything on. But the RCD could also trip with hardly anything on. It was tested and found to be ok.
Would it be legal to have a socket ring on a non-RCD side on its own 32A RCBO. I know it does not cure the problem.
What would I gain to know the earth leakage?

 

[telectrix]

you would need an earth leakage clamp meter. cost from around £90 to £300+ . cost less to get a spark to find the fault.

 

[plugsandsparks]

We can trigger the trip if we "rev" the electric appliance, i.e. start repeatedly. We can also trip the socket ring on the RCD side with a light switch being flicked on and off at speed with the light ring sitting on the non RCD side. Sometimes the RCD does NOT trip with almost everything on. But the RCD could also trip with hardly anything on. It was tested and found to be ok.
Would it be legal to have a socket ring on a non-RCD side on its own 32A RCBO. I know it does not cure the problem. There is no other way
What would I gain to know the earth leakage?

For a start you would not be wasting time trying to make it trip by rapid switching. You can measure the leakage that the RCD is seeing at anytime, you can introduce loads one by one and in combination, you can also see if the leakage is fluctuating due to external factors. You can also check live and neutrals are balanced on each cct just in case its not wired correctly. There will be a pattern you are just not seeing it.
Good Luck finding it.. generally they never improve so it may become more obvious over time.

 

[Octopus]

For a start you would not be wasting time trying to make it trip by rapid switching. You can measure the leakage that the RCD is seeing at anytime, you can introduce loads one by one and in combination, you can also see if the leakage is fluctuating due to external factors. You can also check live and neutrals are balanced on each cct just in case its not wired correctly.
Good Luck finding it.. generally they never improve so it may become more obvious over time.

Only if the OP has the necessary tools and knowledge!