New downstairs light fitting tripping upstairs circuit.

[MikeJEN]

Hi all, new to the forum but have been a lurker for a while. I have a problem that I thought I'd put to you guys first before calling in a local sparky to see if I'm missing something.

I've recently tried to replace a light fitting in my lounge downstairs...here is a pic of the old fitting wired up:

I've wired up the red as live, black as neutral and copper as earth to the new light fitting shown below:

Problem is as soon as I connect the last wire in the new fitting the upstairs circuit trips? When the old fitting is replaced everything works fine. I thought the new fitting could be faulty but I've had this changed and the same problem persists. Could it be the wires sticking out the ceiling are tripping somehow? With the old fitting wired up it seems ok but it does trip very rarely. The new fitting causes the circuit to trip as soon as its connect and even before I put power through the circuit and try to switch it on.

Also, I'm replacing a fitting with one bulb to a fitting with 4, but the tripping upstairs circuit is still there when I try to fit the new 4 bulb fitting with only one bulb in.

Any help will be much appreciated.

Thanks
Mike

 

[mikeyd]

What, exactly is tripping? Nice photos, can we have one of your consumer unit, including the things that trip?

It sounds to me like a 'borrowed neutral' problem. google it. Also bear in mind that if you touch a neutral wire, even if the circuit isn't live then you may still trip an RCD.

And get some earth sleeve for that 'copper' conductor.

 

[ban-all-sheds]

It sounds to me like a 'borrowed neutral' problem.

How would that result in a trip with one light and not with another?

 

[Lectrician]

And it would not occur with no lamps in either (and the OP says no lamps have been fitted yet).

Difficult to judge - We need to know exactly what is tripping.

 

[MikeJEN]

Thanks for the responses so far, here is a pic of the CU

The switch with RCD is the one that trips. It trips even without any light fitted if the wires accidentally touch. It also trips when the last wire to the new fitting is connected. It seems fine with the old light fitting. I have googled about a borrowed neutral set up. Is it actually dangerous or just impractical? I can understand why it may seem I have this set up but doesn't explain why the old light fitting poses no issues but the new one trips the RCD.

Also, I have only just moved into this property. Before moving in I paid for a general circuit inspection which got a satisfactory report with no raised issues. Is a borrowed neutral (if this is the issue) something that should have been picked up?

Thanks
Mike

 

[bernardgreen]

These fittings appear to use a bracket that is screwed to the ceiling.

Does the trip only happen when the fitting is attached the the bracket

Did you have to change this bracket and is it possible that when you did a fixing screw could have punctured the cable in the ceiling ?

 

[MikeJEN]

Yes, the fitting uses a bracket screwed to the ceiling, but i am using the existing holes for the new bracket. The RCD will trip only sometimes with the old fitting....but it 100% always trips when the new fitting is wired up...and not even when it fixed to the bracket.

I suppose it is possible that an existing screw has punctured a cable, but still unsure why the old fitting works and not the new one?

I'm confused. Also, does this seem a big or small job to rectify? I intend of changing a few other fittings in the house...will this issues of the new light fittings not work be present upstairs?

Cheers
Mike

 

[winston1]

Looks like an earth/neutral short in new fitting. Test it with a multimeter on ohms.

 

[JohnW2]

The switch with RCD is the one that trips. It trips even without any light fitted if the wires accidentally touch.

That. in itself, is not unexpected (if the black and earth touch).

It also trips when the last wire to the new fitting is connected.

Is that true regardless of the order in which you connect them? In particular, if you connect the red wire last, does it not trip until you connect the red wire, or does it trip after the first two have been connected (i.e. before you connect the red wire)?

Kind Regards, John

 

[MikeJEN]

The switch with RCD is the one that trips. It trips even without any light fitted if the wires accidentally touch.

That. in itself, is not unexpected (if the black and earth touch).

It also trips when the last wire to the new fitting is connected.

Is that true regardless of the order in which you connect them? In particular, if you connect the red wire last, does it not trip until you connect the red wire, or does it trip after the first two have been connected (i.e. before you connect the red wire)?

Kind Regards, John

I think i connected the Red first, but not too sure to be honest. Will have another go at it tonight.

 

[MikeJEN]

Looks like an earth/neutral short in new fitting. Test it with a multimeter on ohms.

i initially thought it was an issue with the new fitting so i took it back to the retailer and swapped it over for a new one. The replacement fitting presents the same issue. I suppose there could be an issue with the second new fitting, but what are the odds.

 

[JohnW2]

Is that true regardless of the order in which you connect them? In particular, if you connect the red wire last, does it not trip until you connect the red wire, or does it trip after the first two have been connected (i.e. before you connect the red wire)?

I think i connected the Red first, but not too sure to be honest. Will have another go at it tonight.

OK. As others have said, the most 'obvious' explanation would be that there was a neutral-earth fault ('short') within the fitting (and the replacement fitting, which I suppose is not totally impossible, if it were a 'batch' problem). If that were the case, the RCD would trip as soon as you had connected the black (neutral) and earth wires, even if you hadn't yet connected the 'live' (red) wire (just as the RCD would trip if you touched the neutral and earth wires toigether). As others have also said, if you have a multimeter, checking to see if there is a low restistance between the neutral and earth terminals on the fitting would be the easiest way of identifying such a fault (if it exists) in the fitting.

Kind Regards, John

 

[MikeJEN]

Is that true regardless of the order in which you connect them? In particular, if you connect the red wire last, does it not trip until you connect the red wire, or does it trip after the first two have been connected (i.e. before you connect the red wire)?

I think i connected the Red first, but not too sure to be honest. Will have another go at it tonight.

OK. As others have said, the most 'obvious' explanation would be that there was a neutral-earth fault ('short') within the fitting (and the replacement fitting, which I suppose is not totally impossible, if it were a 'batch' problem). If that were the case, the RCD would trip as soon as you had connected the black (neutral) and earth wires, even if you hadn't yet connected the 'live' (red) wire (just as the RCD would trip if you touched the neutral and earth wires toigether). As others have also said, if you have a multimeter, checking to see if there is a low restistance between the neutral and earth terminals on the fitting would be the easiest way of identifying such a fault (if it exists) in the fitting.

Kind Regards, John

Cool, I don't have a multimeter but can pick up a cheap one from Maplin on the way home tonight.

I am a complete novice when i comes to electricals so excuse my stupidity...when I'm checking the fitting is low resistance good?? I check the resistance when its not wired up right? I've read an online tutorial on how to use a multimeter...just want to know how to interpret the results.

Thanks again for everyones input so far...really appreciate it.

Mike

 

[EFLImpudence]

Disconnect the light fitting.

With the meter on low ohms (beep) there should be no measurable resistance (infinite - 1) with probes at the terminal block measured between L & E and N & E.

If, as is suspected you have a short circuit, you will get a reading and a beep between N & E.

 

[MikeJEN]

Disconnect the light fitting.

With the meter on low ohms (beep) there should be no measurable resistance (infinite - 1) with probes at the terminal block measured between L & E and N & E.

If, as is suspected you have a short circuit, you will get a reading and a beep between N & E.

Great, will have a look tonight and see what i get and will keep you all posted.

Cheers
Mike