RCD tripping

[diy-newby]

Hi

Need a bit of help regarding the RCD tripping on my consumer unit. At the weekend the RCD tripped, knocking off the sockets. Tried resetting but it wouldn't, kept flicking back to the OFF position. Turned off all the sockets and narrowed it down to the fused spur which feeds the central heating control panel which was causing the RCD to trip. Turned the fused spur back on and it would trip again. Waited a couple of minutes, then tried again and this time the RCD did not trip.

This morning, the same happened again, the RCD tripped and again, leaving the fused spur turned off I could reset the RCD. This leaves us with no central heating. I switched off the cooker switch and turned on the fused spur and it did not trip the RCD.

Anyone any ideas?

TIA

[Palindr☻me]

The device detects the sum of all the earth leakage currents on all the circuits connected through it. It is very possible to get a number of faults, none with a large enough current, yet, to trip the device but together they do.

For example - the insulation within the cooker has deteriorated such that 20mA of leakage current is now flowing. This won't be enough to trip the device, if it is a 30mA one. The insulation within, say, the central heating pump has also deteriorated such that 18mA of leakage current is now flowing. Again, insufficient to trip a 30mA unit, on its own. Switch them both on, 48mA flows and the device trips.

Or it could be that you have half a dozen devices all leaking 4mA - giving 24mA and not tripping the device. Switch the cooker on and it adds another 5 mA - still not enough total current leaking to earth. Now switch the central heating on, another 5mA - and the trip operates.. Switch either the central heating or cooker off and the total leakage current drops below the trip level.

You really need to know what the situation is and get it fixed.

[the_constructor]

Has your next door neighbours been doing an electrical work in their houses ..... ?

I ask, because, a friend of mine put a socket in his living room and everytime he used it, it tripped the electrics next door. He asked me to have a look at it for him and I discovered that he had wired it incorrectly. Once put right, next door had no problems.

Wierd I know.

[John Whitworth]

I had a very similar problem after a storm was in the area. After what seemed like hours of disconnecting circuits, I traced it to the fused spur itself...i.e. the fuse casing. Replaced it, and all was fine. I can only conclude that somehow, during the storm, the insulation had deteriorated to such an extent in the fuseway that it caused the tripping out.

JW

[ARWadsworth]

If the RCD trips when the boiler fires, not just when the fused spur is turned on then you are probably looking at a pump problem. Ideally central heating systems should be on the non RCD side of a CU

Adam

[ARWadsworth]

RCDs can trip anytime after the halfway mark of the rated trip current. So a

30mA RCD may trip at 16mA.

Adam

[Palindr☻me]

The principle still holds - the OP was asking how come he could have either the cooker on, or the heating on, but not both on - without the trip operating.

IIUC ;)

[ARWadsworth]

The principal still holds (well spotted Sue), but the OP said s/he lost the power to the sockets. Maybe a clearer view of the OP's CU layout could shed more light but I will still put money on a dodgy pump.

Adam

[William4]

Rubbish, if there's an EL fault you want the fault detected. Who wants a bit (or more) mains stuck on their heating pipes to save a problem tripping their power. It is indeed annoying, can be tricky to locate, but if working the RCD is doing it's job.

Reminds me of the Spanish hotel who inserted an earth isolation plug (I kid you not) because we complained that if the cooker was on (and heating) and we touched the sink we felt a sharp tingle (made you jump) !!

My money is only the CH circuit/s having a fault, pump yes, diverter valve yes, controller fault yes.

I have, in the past, comprehensively tested an 'external' ELB for an outhouse, both when new and after a number of years. The trip value was as low as 6mA (reliably) and whilst I can't remember the timings was also well below the maximum spec. Good job really as a 30mA rating may stop nuisance tripping but 25mA is the rated danger current through the central body (and heart) and you do not want to get near that.

[malc]

I had a problem with my Baxi Bermuda backboiler. The heat exchanger was clogged so when it lit the flames went round the side instead of up the middle [1]. This burnt the insulation on the mains cable to the control unit and caused the RCD on the consumer unit to trip. Unfortunately the burnt insulation was inside a duct in the boiler so it wasn't visible immediately. I checked out the pump and all sorts of things before I found it.

I disagree. If mine had not been on the RCD it could have caused a fire.

[1] Lack of servicing, now sorted.

[Andrew Gabriel]

How?

[ARWadsworth]

The pipework will be earthed and the CH fuse will trip.

Adam

[malcolm.white]

Excess current flow in a cable passing through wooden partitions frinstance.

[diy-newby]

It has been fine since yesterday. CH on and the cooker plus the usual tv / pc on as well and the RCD has not tripped. Seems to be an intermittent problem. Turning the CH on and the cooker on at the same time does not always trip the RCD. Just when the RCD trips, turning the CH fused spur off allows me to reset the RCD. Turning this back on will trip the RCD. Wait a while and I can turn it on and it will be ok for a while

[Palindr☻me]

It hasn't "been fine" - it is simply that the fault currents haven't added up to enough to trip the device.

This "intermittent" problem could be water leakage/condensation only being in present in sufficient quantities and in contact with power-carrying conductors under certain conditions and, say, not present or evapourating off under others. Even when not tripping, there could easily still be enough water to be present to be corroding wiring and electrical units - until the damage becomes so great that a permanent fault develops.

What I would do is to isolate parts of the system and test them with an insulation tester - which will localise the problem(s). At this stage it could be extremely inexpensive to fix - just a displaced seal needing to be repositioned, a bit of silicone sealant needed, a compression fitting needing tightening, etc. Leave it and you risk expensive repairs later..

Good luck

Sue

[Andrew Gabriel]

That will trip the overload or fault current protection. No RCD required in that case.

[ARWadsworth]

If my memory is correct is that the socket that was wired with the live and neutral connected the wrong way round on a TT system.

Adam

[malc]

Possibly but I don't know where my controller gets its power from. The cable appears from somewhere in a cupboard. I presume it's wired direct into the ring main like my immersion heater. If that's the case then the cable which looked to be less than 13 amp might be backed up by a 30 Amp (or whatever the ring main breaker is) breaker. In which case a fault might cause the cable to burn out before the breaker went.