House trips started going..... why?

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Last week we had a minor? change made to the supply wires coming into the house. The electricity company changed the supply wires (from their pole to our incoming fuse) from the 1970's twin wires to a modern single coaxial supply wire. The distance is about 30-40 yards.
Before the change I can't remember the last time the RCCB tripped.
After the change we now have permanent tripping, that started on the same afternoon.
The tripping seems to be load-related, the more things we have on, the more it is likely to trip. eg, To have a shower, (electric, 7KW), we now have to more or less turn the rest of the house off.
Note that the loadings we have on at any one time are no different to those before the cabling change, when we did not have tripping.
It has taken me a few days to go round the house, measuring the leakages (Megger), or selectively isolating various appliances. I cannot find any single suspicious appliance.... except to say that if we have enough appliances off then we do not have a trip during a shower. Things with motors (vacuum cleaner) do seem to trigger a trip.
L-N and N-E voltages are much the same as before the change, 242Vrms and 1-2Vrms each. Although I do feel that the 'dip' of the lights as the shower is turned on does seem smaller than previously.
Can anyone suggest what is going on? Could such an apparently simple change to 30 yards of supply wiring make the trips more sensitive? Is there any mistake they could have made?
For ref; The RCCB in the Consumer Unit is an MK LN5780, 240V 80A, with 30mA tripping current. Between the incoming fuse and the CU is the old original trip, a Chilton "Voltage operated Earth leakage trip, 60A Type D". The MK 30mA always trips, and sometimes (maybe 1 in 5 times) the Chilton also trips.
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Tony Williams. Change "nospam" to "ledelec" to email.

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On Sat, 27 Sep 2003 09:42:27 +0100, Tony Williams wrote:

Give the company that made the change a call and report it. There is something odd going on and RCDs should not trip in relation to the load.
A couple of points from your description.
Is the 30mA RCD in the supply to whole house? If so that should really be a 100mA time delayed device and if you want shock protection on some circuits a 30mA non delayed RCD should be used as required.
Where is the voltage operated trip really loacted you don't mention a meter. If it's pre the meter it is the boards equipment and I'd argue up to them to replace it with a 100mA time delayed RCD. Voltage operated trips are really from the ark these days.
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Cheers snipped-for-privacy@howhill.com
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That does look on cards. I was trying to eliminate us as the problem first.

The RCD supplies the three ring mains and the shower. The lights, boiler, cooker are not on the RCD.

I forgot the meter. Fuse --> meter --> Chilton, --> CU.
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Tony Williams. Change "nospam" to "ledelec" to email.

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One possibility is that on the old set up you were not connected to the electricty company's earth and now you are. Small amounts of leakage current from a number of appliance can trip a 30mA RCD. From memory I think 100mA is recommende/requierd if covering the whole supply.
Your wiring may have been installed perfectly ok to operate without an electricty company earth on the other hand it may not have been or the electricty company earth may have been broken/ accidently disconnected for years.
Earthing is complicated if it was me I would get the electricty company back and ask them what they changed and how it may cause your RCD to trip. If there is still a problem get professional assistance if you don't know what you are doing.
Ian,
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ATM I can't see this. There are two wires only going from pole to pole. There used to be two wires coming into the house, and there are still only two wires coming into the house, except they are now coaxial.

Yes this is an all-electric house so the total load can be high and I have a feeling that multiple RCDs is where we might end up. No room for that in the present CU though. :(
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On Sat, 27 Sep 2003 23:30:29 +0100, Tony Williams wrote:

Where is the transformer? Do you have your own or is it shared?

The neutral will almost certainly be bonded to earth at the transformer or at least it should be. Ours is you can see the wire from one of the transformer LV terminals descending the pole and into the ground.
Though with that old voltage operated breaker I suspect your earth was/is supplied localy. Trace out the earth bonding, if you can. It may well disappear outside to an earth rod in addition to connecting to the incoming service pipes.
I suspect you now either have a better earth than you did before or maybe no earth cause of a cock up somewhere in the change over.
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Tony
For some reason I can only see your reply's an not messages from other posters.
If there is was only two single wires coming into you house you may have had an earth from the electricity company, you may not. I gather you mean you now have a concentric cable (one thicker single black one). This can have either a live and neutral or live, neutral and earth. So it is quite possible that you now have an electricity company earth when you didn't have one before . As I said I ask the electricity company to see if they can sort out what they did to point you in the right direction.
Ian
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The incoming cable goes into the fuse and there are only two cables going from fuse to meter. There is no sign of a new Earth wire anywhere.

I'm going to have to do that probably.....
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Tony Williams. Change "nospam" to "ledelec" to email.

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But then I doubt you have access to a Megger as the OP has...
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*24 hours in a day ... 24 beers in a case ... coincidence? *

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Maybe the electric company did a megga test, and fried your RCD!
I have the same model MK breaker, and have had to replace it recently, not due to a megga test, just seemed to have died, it was about 20 years old! - as soon as we got the new one (same model) the annoying trips stopped!
One thing though, they aint cheap!
Sparks...
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No I watched him..... he tested the new installation with the CU isolated (by the Chilton).
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Tony Williams. Change "nospam" to "ledelec" to email.

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wrote:> > Maybe the electric company did a megga test, and fried your RCD!> No I watched him..... he tested the new installation with

Hi
I'm not quite 100% clear about this, but I detect a possible problem with your setup. The voltage operated ELCB works by disconnecting your house's earthed appliances (including shower) from earth, and tripping when the voltage between the house 'earth' loop and the real earth exceed 50v. To be frank, if you have an electric shower, I would think this was dangerous.
Then we have an RCD, which _relies on_ a proper earth connection somewhere to function. The RCD doesnt need an earth connection itself, but it does need the appilances/wiring to be earthed, one way or another, to be effective.
Now this is one area that's stretching my knowledge a little, but from what I understand of your setup I dont think I'd be volunteering to take any electric showers.
If I have this right: your shower can have upto 50v on it before the Chilton trips your shower is disconneted from earth your plughole probably will be earthed once the water starts running. AND it looks like you have more than 30mA of earth leakage current from your disconnected earth loop thats connected to the shower.
I would say you need skilled advice before you get in that shower again.
Regards, NT
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I too am a bit perturbed by the apparent setup, with both an olde-worlde voltage-operated earth leakage breaker, and a whole-house current-balance one downstream. And as both Nick T and Dave P have suggested, I'd want to ditch the voltage-operated item. Since your hassles have started after the supply co's mods, I'd start with a friendly call to them. Don't bother sounding too clueful on the phone - you want to get a real person from the supply company to come visit your place with test gear and knowledge to hand; don't expect (or accept ;-) a diagnosis over the phone from the person slaving in call-centre hell!
HTH, Stefek
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The RCCB in the CU only feeds the three ring mains and the shower. The appliances with fixed wiring (cooker, c/heating boiler, immersion, lights, etc), are not on that 30mA RCCB and their possible earth leakages would be detected by the old Chilton. It makes a sort of sense.

Yes, I got them back in last week. Three men, two vans and a serious inspection from the pole up to the Chilton. That's the limit of their responsibility (when for free).
They confirmed what I already thought.... they had simply replaced a two-wire feed with another two-wire feed, but in one cable instead of two. Their opinion was that the fault was almost certainly in our RCCB, or downstream of it.
So I hacked an old portable RCCB into a differential current sensor, and have been going around the house looking for possible (multiple) perps.
The electric kettle is known to have (apparently) tripped the RCCB at point of switchoff and it is that stupid design where actual steam is used to heat the bimetallic element. I boiled it a couple of times, but it only showed a differential current of less than 1mA. It's a bit mucky inside the handle so that one is still a maybe for an occasional trip.
Other appliances, mini oven, w/machine, tumble drier, Henry, all show a tiny differential current, of between 0.0 and 0.5mA. The two fridge-freezers haven't been tested yet.
The biggest perp (oh buggerit!) is this computer system. It has a differential current of 1.3mA. And (wait for it) the little mains filter that powers the modem actually has a VDR across Line-Earth. I can only think that fitting a VDR in that apparently daft place is for it to conduct whenever there is an overvoltage surge on the mains, which would deliberately trip the RCCB.
The number of nuisance trips have reduced over the last few days (to zero yesterday). This may (or may not) be due to two changes made. That VDR across L-E has been removed, and the soil around the earthing rod has been thoroughly wetted (this is a clay soil, which I know to be bone dry down to at least 3ft, with major cracks running through it).
Touch wood.....
Thanks for all the suggestions.
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Tony Williams. Change "nospam" to "ledelec" to email.

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Could have been the culprit if your earthing is recently improved. You wouldn't like to post the make and model and approx age of this item you? Is it a "transformer moulded onto a 13A plug"?
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roger

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Noname (yet). All I know atm is that the nuisance tripping *appeared* to reduce when that VDR was removed. The VDR is marked "GE U9 275L40B", which probably means a 275V(rms?) stand-off voltage. So that should be an ok design as long as the VDR is not faulty, and on normal mains voltages.
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Yes.
No, definitely not. Should only be between L & N.

Normal mains voltage includes very short spikes up to several kV, and longer ones of several 100 Volts. During these spikes the VDR is only 100 Ohms or less, so it can put a lot of unbalance current thro the RCD for the duration of the spike if your earth is fairly good. These spikes can trip RCD's anyway on occasion, due to the house-wiring capacitance to earth and filters on electronic gear, without the help of spurious VDRs. If your electrician gives your installation a clean bill of health, but trips still occur, he can ask the supplier to but a transient recorder on site for a couple of weeks to see if your trips coincide with incoming rubbish. Normally foc.
You really didn't want to know all that did you, but maybe it will be useful to someone else following the thread.
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roger

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In this case, replace the ELCB with a Type S 100mA RCD.
Christian.
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Yes, other comments about replacing the Chilton have been noted. We will be getting a leccy in to do that (and a few other things). Thanks for a suggested specific type.
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Final followup;
I found an actual definitive perp. All appliances checked out ok, so isolated the incoming mains and started prodding around inside the CU. Found a Neutral-Earth short, disconnected all N's and found it was on an upstairs ring main, so started hunting for it.... Cutting a very long story, I finally found a low-R between E+N and the head of a nail, above particular 13A socket. Removed the nail, and all probs went away.
We've been having a lot of internal/external work done recently and this nail went in at about the same time as the incoming cabling was changed. I'm not blaming anyone though, because it is only about 2ft above the 13A socket, and a good 8" to the right of it. I now have to remember to warn people of the possibility of diagonal cabling under the plaster.
Note that (with our very low E-N voltage) the E-N short itself did not cause a trip, it required a certain amount of load current on that ring before there was enough unbalance current between the L-N wires.

Leccy's been in and done it, as suggested, thank you.
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