Nuisance Tripping

[Electroguard]

Hi, I would like something to be confirmed before I blow myself up!

First let me set the scene... My property is suffering from intermittent nuisance tripping, sometimes it happens nightly, and sometimes not for weeks, and there is no rhyme or reason (such as specific times or appliances or weather etc).
To make matters worse, the property is in France and has a 30ma RCB built-in to the electricity companies main incoming isolator, so there is no way I can bypass or split it to help pinpoint the cause (I can't speak french yet by the way, and couldn't afford to call out an electrician even if I knew how!).
An added complication is that it's a 3 phase supply feeding 6 single-phase consumer units plus some 3-phase sockets (property was previously a lorry yard which I'm converting to caravan storage and overnight parking). The property is quite old, the wiring is maird', and radial, with some going externally underground to an out-building. When initially trying to find the problem I discovered that one of the phases contacts in the old isolator were welded shut therefore everything on that phase was still live even with the isolator tripped off! I got the power company out and they installed a new one, so I'm reasonably sure the problem is my equipment and not theirs.

Due to the intermittency I think I'm going to have to 'pre-load' the earth leakage current to the point where the faulty item will definitely cause a trip when I connect the offending item/circuit. My ohm's law is nearly 50 years old, but having dusted it off it seems like I should be able to use a 10K 10w resistor to give about 25ma max in series with a 250K variable resistor (if I can get a 10w one) to allow the current to be reduced down to about 1mA (I've 'assumed' 250v instead of 230v for a bit of a safety margin) and with an AC milliameter in series with the resistors so I can see how much added leakage is needed to cause tripping and therefore get a rough idea what the real leakage must be (30mA minus the pre-load value).

So my first question is... should that work?

At the moment I dare not leave the property for any length of time - such as going to England - without risk of another nuisance trip taking out all my local and online security and CCTV etc (browse to www.electroguard.com if you're interested) and spoiling fridge and freezer contents.

So my second question is...

Until such time as I can track the problem down could I use the same setup between L and N instead of L and E to provide an opposite 'offset' leakage and therefore reduce the possibility of tripping in my absence by effectively increasing the required tripping current up to about 55mA (RCD 30 mA + 25mA offset)?

Lastly... I seem to remember that 35mA was accepted as the fatal 'dose' so is presumably why 30mA protection was adopted as standard, but with the premises being vacant would a tripping leakage of less than 60mA still provide safe protection for the property?

BTW - I deliberately posted in the UK and not the 'Overseas' category (even though the property is overseas) because the actual problem and questions are not really location specific, and therefore are answerable by non-french expertise.

Thanks in advance for any advice.

 

[Electroguard]

Another thought is... I don't have a clamp meter but they seem cheap enough, so if I got an AC milliampere clamp meter could I read the earth leakage current with that?
Would that be a practical way of tracing any high leakage back from the incoming RCD Isolator to its specific circuit and possibly even device?

 

[ban-all-sheds]

Mod - Given that the location of the OP's property is utterly irrelevant to the electrical aspects of his question (the laws of physics being the same in France as here), and particularly considering his comment about why he posted it in the UK forum, why did you feel the need to move this topic?

Electroguard - if you get no joy, re-post in the UK forum, but omit the part about it being in France....

 

[ban-all-sheds]

The property is quite old, the wiring is maird', and radial,

Nothing wrong with radials.

with some going externally underground to an out-building.

If you don't need power in the outbuilding you should disconnect that cable at the source, to rule out the possibility of that being the cause.

I'm reasonably sure the problem is my equipment and not theirs.

Probably, but you should get the RCD checked.

Due to the intermittency I think I'm going to have to 'pre-load' the earth leakage current to the point where the faulty item will definitely cause a trip when I connect the offending item/circuit. My ohm's law is nearly 50 years old, but having dusted it off it seems like I should be able to use a 10K 10w resistor to give about 25ma max in series with a 250K variable resistor (if I can get a 10w one) to allow the current to be reduced down to about 1mA (I've 'assumed' 250v instead of 230v for a bit of a safety margin) and with an AC milliameter in series with the resistors so I can see how much added leakage is needed to cause tripping and therefore get a rough idea what the real leakage must be (30mA minus the pre-load value).

So my first question is... should that work?

It will "work", but if your problem is cumulative intermittent leakage from old "merde" cables you may still not be able to track down an identifiable culprit. You need an insulation resistance check done on all the wiring...

Until such time as I can track the problem down could I use the same setup between L and N instead of L and E to provide an opposite 'offset' leakage and therefore reduce the possibility of tripping in my absence by effectively increasing the required tripping current up to about 55mA (RCD 30 mA + 25mA offset)?

Won't do any good at all - a connection between L & N won't generate leakage, it will just be a regular load, the same as any appliance.

Lastly... I seem to remember that 35mA was accepted as the fatal 'dose' so is presumably why 30mA protection was adopted as standard, but with the premises being vacant would a tripping leakage of less than 60mA still provide safe protection for the property?

Oh yes - 100mA would be fine, but the problem is you can't replace the RCD...

 

[ban-all-sheds]

Just seen your post ban, now moved back to Electrics UK

Ta!

 

[Electroguard]

Thanks for the response anti-shed man.

I've ordered a 10mA RCD today - to put into the distribution panel - with the intention of connecting each of the circuits through it in turn, hoping that the leaky one will trip it instead of the incoming 30mA one and let me narrow things down a bit.

It wasn't particularly cheap, and I'm on a rather wobbly financial tightrope, so to save wasting money on the wrong thing I'd appreciate any possible suggestions or recommendations for a cost-effective tester that would be suitable for the purpose?

 

[ban-all-sheds]

There aren't any - RCD testers aren't cheap - in the £'00s.

As are insulation testers.

Basically, a new set of, or all-in-one, testers is going to set you back £500-700, and s/h on eBay at least half that...

 

[retirednow]

A friend has a similar problem. Their entire house is on a 30mA trip. A while back they had a trip caused by plugging in a dusty convector heater that had not been used for six months. The slight leakage through it was the last straw that broke the camels back.

IMHO (and this agrees with the IEE) 30mA trips are only recommended for FINAL circuits. For a whole building a 100mA trip is adviseable. Of course this then conflicts with the 30mA rule so you really need to put 30mA trips into the finals. This can be a great nuisance if the consumer unit will not accept miniature trip switches (RCDs)

By the way in France the term is Interrupteur Differential. Same thing as Ground Fault Circuit Interupter in the USA and Residual Current Device in the UK.

Make sure that you get one that is current operated (has a little transformer in it) Voltage operated devices are no longer legal as far as I know but there may still be some old stock in some parts of the world.

At least you don't have the two jags nonsense over there

 

[JohnD]

some kind soul posted a translation of a french Wiring book recently. you will probably find it if you browse the non-UK electrics forum.

I think you need to have the 30mA whole-house RCD removed and replaced with RCBOs and/or a less sensitive one or a simple isolator. but it is up to you to understand the french regulations and find a suitable person. I expect you are contemplating the effect of moving to a foreign country without understanding the language

BTW earth leakages are most commonly on:
Outside circuits (including outdoor lamps) that get rained on
Watery appliances like immersions; boilers, pumps; kettles; tea urns
Heating elements including ovens and cookers
Very old cables
Cables that have had nails driven into them

so you could start by isolating all of those.

It is entirely possible that you have ten faults of about 3mA each, so you may not find a singe circuit or appliance that is to blame.

 

[plugwash]

I think you need to find a good local electrician who is both an expert in local regs and speaks good english. A 30ma RCD covering the whole install is totally inappopriate for a big three phase install and you should find out if there is any way to get it removed.

I wonder if there is a market for a device that sits downstream of a RCD detects the leakage and cancels it out. would be quite tricky to design though.

 

[Spark123]

Like a transformer you mean?

 

[luminaire]

Here is an English speaking electrician working in France.
I got on the "French Wiring" on the 'electrics outside the UK forum. His name is Badger
HTH

 

[plugwash]

Like a transformer you mean?

Using an isolating transformer is certainly an option but rather bulky and expensive.

I was thinking of an electronic system that measured the imbalance in the same way an RCD does (pretty easy, you just put the two conductors through the same CT coil) but rather than having a trip mechanism having a system to create equal and opposite leakage.