problem with RCD

[che gomez]

Hi, my names Rob, been working for company's in the Birmingham area for the last few years but have now gone on my own and have my part p in jan. I Have a problem with a job i am going to have a look at soon.The customer has a small garage/workshop that was recently wired and contains basic stuff some sockets and lights but does plan to plug things like compressor, heaters and other machinery to ringmain. The workshop is feed from a 6mm armored from existing fuse board in house on 32a breaker whitch is then protected by a 30ma RCD. The problem is when to many thing are running in the workshop its tripping the RCD in the house (not the MCB).
It sounds like over load but its not tripping the individual MCBs in the workshop or the house. Im thinking it might be a faulty device being plunged in but he says when he runs an extension lead off the house circuit it doesn't happen. It could be The wiring but all the circuits work fine its just seems to be when there is to much load on the ring main and if there was an wiring fault (damage or short) the RCD would not come back on at all......would it?

 

[Dan]

Hi che gomez and welcome to www.electriciansforums.net!

 

[Richard Burns]

Hi there and welcome to the forum.

You may find that if you post this query in the general electrical forum you may get more response.

The likely problem here sounds as if there is a link between neutral bars so that the RCD has two paths for the neutral current one of which is outside the RCD so when a high current is flowing there is enough imbalance to trip the RCD.

 

[ringer]

A link between neutral bars would trip the rcd instantly and the rcd would never reset. I assume there is a garage board because you mention mcbs in the garage. Is there not a rcd in the garage board? If it was recently wired then I would expect that board to have a rcd (proabably rcd main switch). I would also expect the 32A mcb in the main fuseboard to be not on a rcd - particularly if garage is fed by swa. Methinks dicrimination problem. You need to explain the circuits in both boards better for us to help further (RCD or not, how many circuits etc)

 

[che gomez]

the feed is taken from a 32a mcb that is on the protected side of the board (30ma RCD that serves 5 circuits on that side) that then goes to a basic 4 way board in workshop in garage with no RCD just 100a main switch.
none of the breakers in the workshop have tripped. Also of note is the feed taken from 32a mcb in board was already feeding one ring main in house ie that breaker is now feeding workshop and ring main in house! but not tripping mcb for overload just the RCD

 

[HandySparks]

With the RCD tripping but not any MCBs, it sounds like a live to earth fault. Could be in the garage wiring, but more likely in the equipment used in the garage (as the RCD trips when more equipment is plugged in). You could start by checking leakage currents if you have a suitable clamp meter or you could measure the live (L+N) to earth insulation resistance of the whole garage installation. I'd also try the same test with all the garage equipment plugged in and switched on to see if the fault's there. (Might be best to be a bit cautious and do the test at 250V). It could be that the tripping is caused by cumulative leakage from a number of appliances rather than by just one item.

 

[HandySparks]

It bugs me when a topic is re-started in another thread. You take the trouble to reply and then find that you've missed a load of other posts and your contribution is pointless. If you're going to do this, or advising someone to do this, can you please put a note in the original thread to say "this conversation is continued in a new thread" or similar.

No offence intended to this particular OP.

Edit: Much better to ask the moderators to move the post rather than start again.

 

[Richard Burns]

You may find that if you post this query in the general electrical forum you may get more response.

I did recommend that this thread be opened in the general electrical forum for better response rather than the introductory thread where it may be missed. I should have mentioned that this would generate a duplicate and that this original thread should be edited, sorry.

 

[MarkieSparkie]

Hi, welcome to the forum.

 

[Guest123]

Welcome along.