help with rcd trips, France

[wibbome]

Hi guys, need some advice please. I've got a problem on a French 3 phase CU. Basically the 3rd phase rcd trips when the boiler circuit on the 2nd phase is on whilst a sockets and lights circuit on the 3rd phase is on. If i turn off the sockets and lights mcb (there on the same circuit) then there's no trip and vice versa. Its only just started happening recently aswel I've been told and the client said nothing has been done to the installation. I've checked all the fittings for decent connections and everythings fine. I can't quite understand why its two separate phase circuits are affecting each other. Any advice will be gratefully welcomed, thanks.

 

[Engineer54]

Sounds as if you have neutral interconnection problem there, so i wouldn't completely believe the client saying nothing has been done to the installation!! You need to get your test equipment out and start testing between these two circuits...

Are you saying that a single MCB is controlling both a lighting and outlet circuit?? So what's the rating of this dual purpose MCB then?? lol!!

 

[Richard Burns]

I would agree with E54 something has changed!
It is possible that the two cables run close to each other and have worn together.
If it is only when the MCBs (assuming they are not double pole MCBs) are on and not when the boiler, lights, sockets are drawing power then it is N-E, N-N fault otherwise L-E.
Try a continuity between the neutral bars for the two phases.

 

[wibbome]

Cheers for the replies. Yep should have mentioned that there is no separate neutral bar, all the breakers are double pole and the neutral is linked between the 3 rcds. And its an older French installation so yeah the lights and skts are on a 16amp mcb. Crazy i know but they still allow it as long the skts are rated at 16a and only used for lamps! Ill have to quiz him more to see if anything has changed. But to clarify its when the boiler is on and the skts are on but without any lights or power being drawn that it trips. when the boiler mcb is on but not drawing power, because its set on to come on at peak times, and the skts mcb is on it doesn't trip. When the boiler is on and skts mcb is off it works fine. Stumped!

 

[SPARTYKUS]

Cheers for the replies. Yep should have mentioned that there is no separate neutral bar, all the breakers are double pole and the neutral is linked between the 3 rcds. And its an older French installation so yeah the lights and skts are on a 16amp mcb. Crazy i know but they still allow it as long the skts are rated at 16a and only used for lamps! Ill have to quiz him more to see if anything has changed. But to clarify its when the boiler is on and the skts are on but without any lights or power being drawn that it trips. when the boiler mcb is on but not drawing power, because its set on to come on at peak times, and the skts mcb is on it doesn't trip. When the boiler is on and skts mcb is off it works fine. Stumped!

Seen the lights/ sockets on same circuit (Belgium as well). Like the double pole MCBs though.

As above, get the tester out and do some continuity / IR tests.

 

[Victor]

Cheers for the replies. Yep should have mentioned that there is no separate neutral bar, all the breakers are double pole and the neutral is linked between the 3 rcds. And its an older French installation so yeah the lights and skts are on a 16amp mcb. Crazy i know but they still allow it as long the skts are rated at 16a and only used for lamps! Ill have to quiz him more to see if anything has changed. But to clarify its when the boiler is on and the skts are on but without any lights or power being drawn that it trips. when the boiler mcb is on but not drawing power, because its set on to come on at peak times, and the skts mcb is on it doesn't trip. When the boiler is on and skts mcb is off it works fine. Stumped!

Shared neutrals between different rcd's will cause them to trip, you may find that somewhere in the instalation there are several junction boxes, people here in France love connecting new circuits for either lights or sockets from these, then when they get a problem they call an electrician and say that it has never been touch and that it has not happened before. Check for JB's or shared neutrals in the CU.

Alsom would like to say that here in France, socket circuit can be run on 16amp mcb's and not as you say just for lights, however you are only allowed 8 sockets in total on either a 16amp or 20amp circuit.

 

[Victor]

Just had a thought, check the neutrals between the sockets mcb and the day/night contactor circuit, thats where I would look first.

Also there should be a 2amp mcb protecting the contactor, I have seen that used to run to a CU secondaire and cause a similar problem. Is there more than one CU in the house?

One word of WARNING, dont just change anything over to an alternative RCD, The French electricians love using junction boxes not only for lights but also for other circuits, especially if they are running low on cable (dont laugh). If you were to move the socket mcb over to the next range up you could end up putting 400v though other circuits without knowing it.

 

[Engineer54]

Where is our French electrician ''WilcoxElec'' when you need him?? ...lol!!

 

[wibbome]

Hey guys, so i checked the neutral on the contactor and hey presto it was interlinked. Sorted it all out and everything was fine, all boilers, skts and lights are on. Excellent, until i get phone call later on saying it had tripped again. So i didn't check for JBs before as i thought it was solved so i will be thorough now. Haven't seen any other CUs but it is quite large so will check for that also. Many thanks so far and i will tell you my findings and hopefully the problem!

Yep you're right Victor about the 8 skts on a 16amp mcb, i was immediately thinking of the 2 skts via a light switch on a 16A mcb wired in 1.5mm, my apologies

 

[Victor]

Sometimes EDF give customers a two hour cheap rate boost either at lunch time or mid afternoon. Could the contactor 'kicking in' have caused the trip out. If so, I would check out that there is not another CU with another contactor and 2amp mcb and that the feed to the CU you are working on is not fed from the other. The two cheap rate pilot lines should feed direct from the electric meter.

Hope this helps.

 

[Victor]

Where is our French electrician ''WilcoxElec'' when you need him?? ...lol!!

I'm here and a I'm a French electrician.....lol!!!

 

[Engineer54]

I'm here and a I'm a French electrician.....lol!!!

I thought you were a British ''Pseudo'' French electrician!! ...lol!!:devilish:

 

[WilcoxElec]

Where is our French electrician ''WilcoxElec'' when you need him?? ...lol!!

Could have emailed me...... Answer is always neutrals crossed on bipolar MCB --- often on ... e Va et Vient circuits -- nearly always one of them that gets crossed between the lighting MCBs ----- seen it many many times---- and it often happens during rewiring - replacing fuses with MCBs ...... --- So it was the Chauffe eau contacteur..... Yep .... Good ........ Been very Busy

 

[Victor]

As I said, always go for the chauffe eau contactor first, can save a lot of time.


Got a call out the other day, client said that there are 4 exterior lights on one switch, when switch is on, there are 3 lights off and 1 on..... with switch off there are 3 lights on and 1 off. Pinched neutrals here we come.

 

[wibbome]

Hey guys sorry i haven't been on for a while and replied to you lot but thanks for the many replies.

Victor, yeah the edf midday boost was the reason for the trip. So thoroughly checked the neutral and connections and for junction boxes and that the board has its own supply which is is all fine. The only thing i could say is that the contactors share the same switch wire from the edf meter which shouldn't matter.

Wilcox, didn't get chance to check the va et vient circuit, i couldn't say i noticed that circuit but i wasn't looking either.

I have suggested a rewire for the room only, to separate the lighting and skts circuits as i cannot access any of the wiring of the lighting circuit as its all behind wood cladding and there's no accessible junction box. I will check for that circuit first and test it and if the problem presents itself then im sure the client will be happy!

As always gentleman your advice is always sound and appreciated, thanks.