Neutral Inter Connections

[dmh]

I've been investigating a problem today with an RCD that keeps tripping. I have discovered that on one of the ring circuits that is RCD protected there is a neutral connection to the non rcd side of things but for the life of me I cannot track down where it occurs. Any suggestions from anyone as to how to find this and is this likely to be the cause of the RCD tripping (customer is adamant that nothing has changed recently and the RCD problem has only just started happening)

Thanks

 

[davelerave]

may not be that

is it random trips?

you may get a reading across if IR readings are low-what sort of reading?

whats the IR readings like on the outgoing side of rcd?

 

[dmh]

may not be that

is it random trips?

- Not really random, trips when shower is on and then say kettle switched on in kitchen and that type of thing.

you may get a reading across if IR readings are low-what sort of reading?

- IR readings within the circuit are fine.

whats the IR readings like on the outgoing side of rcd?

- Not entirely sure what you mean by this

 

[davelerave]

the IR on outgoing side of rcd- with rcd in off position

leakage may be accumulating by the sound of it

 

[dmh]

Sorry to maybe seem a bit stupid but I am a bit new to this fault finding stuff. If i test this and find that i have poor readings what would this suggest the fault is?

 

[pushrod]

the rcd is detecting an imbalance between the line and neutral currents ie an earth leakage fault. Low IR reading between lives and earth could be responsible for the rcd trip, ie 30mA of current "leaking" between a live and earth. Sometimes rcd trips can be due to cumulative effects of lots of small earth leakages from several sources - lots of electronic devices will quite naturally contribute a small earth leakage, particularly computers. As the shower is a common factor have you had a look in their to check their are no small leaks.

 

[davelerave]

ya can be damp inside unit or low IR on 'heater tank'

that and kettle should be worth a quick look

 

[dmh]

I did start with the shower and insulation resistance between all conductors was perfect (>299M ohms on my Megger). I then moved on and happened to notice that when I had the ring feeding the kitchen diconnected (live, neutral and cpc all disconnected at CU) I was getting a continuity reading between the disconnected neutrals and the non rcd neutral bar which didnt seem right and hence my original comment about an inter connected neutral somewhere.

 

[dmh]

Incidently, the shower itself isn't connected to the RCD that is tripping.

 

[davelerave]

was it in the ohms range or megohms range?

the reading across circuits

 

[dmh]

Yes that was megaohms and it was the final circuit, not the shower itself.

No sign of any dampness in shower and trips almost immediatly so dont think its water getting into shower unit.

Not sure how would I check the IR on the shower itself.

Also as just mentioned the shower isn't on the RCD that is tripping.

The kettle has been replaced and problem persisted so dont think its the kettle either.

 

[Jimmyb]

have you ir tested between different circuits (neutral's & earth)

 

[pushrod]

Not sure how would I check the IR on the shower itself.

.

Put line and neutral in one croc and earth in the other, test at 250V

As mentioned above worth checking all neutrals to earths and have you double checked that all neutrals are going back to the correct neutral bar?

 

[dmh]

I have checked that all neutrals go back to the correct bar and I will check the IR on the shower tomorrow and see what i get. Sorry to keep harping back to this but if the shower is faulty why would it cause the RCD to trip when the RCD in question isn't protecting the shower.

 

[pushrod]

does the bath/ shower cubicle leak in any way? I have heard of the shower tripping an rcd when really it was not the electrics of the shower but the effect of water from it affecting the power sockets below - worth a look.

 

[dmh]

The shower is downstairs so not as though water is leaking through and down onto anything and I would say that its happening too quick for it to be water leaking somewhere it shouldn't. Turn shower on, turn kettle on and it trips. Incidently kettle on it owns works fine or at least it seems to when i test it but customer has said that sometimes tripping does occur when shower not in use.

 

[pushrod]

Might be worth trying to get customer to keep a log of what appliances are on when the rcd trips - you could be in the unlucky position of having more than one cause. Anything with electronics washing machine , microwave etc etc could be contributing.
[ you sure the sockets ring isn't running nearby in the wall , clutching at straws with the water leaking]

Edit : just a quick check - we are talking electric shower and not a power shower aren't we?

Edit again : have you tried ramp testing the rcd?

 

[Jon Bridges]

You say you have linked between the neutral on the side with the RCD and the other side but if you do each circuit individually you may get a better understanding, ie a borrowed neutral for a lighting circuit perhaps. Once you know which 2 circuit neutrals are connected you can wanderlead across the 2 circuits to track down the problem.

It takes a while, had a nicked neutral cable touching the backbox last week (causing a short between earth and neutral). When I pulled the sockets I couldn't find the fault. Took bloody ages to work out what was going on, and no it wasn't me that nicked it!!

 

[malcolmsanford]

Good idea to ramp test the RCD. It may just be that. As noted in a previous post quite a lot of modern appliances have High Earth currents and you could be leaking a few from TV. computers. Washing machines etc, a 30Ma RCD will most likely trip in the late 20Ma but if the RCD is old or somehow not quite up to standard it might be tripping a lot lower, perhaps below 20Ma. A ramp test will tell you what it is tripping at.

 

[La Poste]

Is the shower bonded, bonded into another circuit I mean? You know bathroon cross bonding and going into the light cpc and all that.
Just a thought.

 

[jibjob]

Don't know if this will help but had a similar problem few years back. Rcd tripping intermittently, but only when load reached a certain level. Thought it was kettle at first but if you ran it with everything else ie TV, video etc unplugged it wouldn't trip. Add say the TV & vid back into equation, off it would go. Eventually traced to a spur from the ring that ran under the carpet between the skirting and the carpet gripper, not a great idea in the first place but even worse when the cable runs across the gripper which has lots of little pins sticking out of it. Turned the cable over and there were loads of indentations/punctures in the mechcanical protection. A very small amount of current must of been leaking via the gripper but only activated the rcd when the load on that circuit reached a certain level. Re-wired the spur properly, problem sorted.