5A lighting circuit, connect L and N or L, N and earth?

[TheLastMan]

Had a nasty short in a 5A lighting circuit in our new house. Fuse was blowing weekly. The end of an old steel pipe under the bathroom floor was cutting into the cable supplying the kitchen ceiling lights every time someone stepped on a floor board. Took us a while to work out what was happening until wife stepped on offending floorboard to accompanying flash, bang and smell of burning plastic. On lifting the floorboard we found the cable had been mashed by the pipe and the plastic insulation had melted.

Rushed out this morning to B&Q and bought a 5A connector that contained two brass connecting blocks in a plastic housing with cable clamps at each end.

Removed the offending pipe and cut out the mashed section of lighting cable to wire into the connector. The cable contained two 1mm insulated single core copper conductors, one red and one black. In between was a bare copper 1mm earth conductor. Now I thought a 5 amp lighting circuit would be just two wires? Do I need to connect the earth as well?

At the moment I have wired just the two live conductors and trimmed off the earth conductors but am worried that I have done the wrong thing. I am running out of slack on the cable and want to avoid rewiring if I can. Otherwise I will have to buy a short length of lighting cable and splice it in with two connectors. Not ideal!

I can confirm that this circuit is purely for lighting, serving 8 ceiling mounted lights on the ground floor. All are 15w low energy bulbs so the load is about 120w (0.5 amps). The fuse is of the old fashioned melting wire type held down by two screws in a ceramic block. I am using 5A wire for this.

I can buy a 13amp connector with three connecting blocks to do this job if necessary.

 

[davy_owen_88]

You must ensure earth continuity, so cutting the earth conductor off is not a good idea. But another 5A connector block and connect the earth conductors to that, remember to sleeve the bare conductors with green+yellow sleeving and then fit the whole lot in a choc-block

Another point to remember is that all screw terminals must be accessible - under floorboards is not really accessible if you have carpets/laminate flooring etc.

Davy

 

[TicklyT]

Yes, you do need to connect the earth as well.
If you don't it may compromise the safety of the complete lighting circuit.

any metal parts (including the screws fixing plastic light switches to the wall) may become 'live' under fault conditions if the earth conductor is disconnected, and it takes a lot less power to kill than it does to blow a 5 Amp fuse!
I believe the 5A and 13A connectors you have referred to are intended for jouning appliance flex rather than cables. Probably better to use a junction box, or a choc box and choc block.
If it is accessible, consider the possibility of replacing the complete run of cable to avoid the problem of any inaccessible connections.

 

[TheLastMan]

Yes, you do need to connect the earth as well.
If you don't it may compromise the safety of the complete lighting circuit.

any metal parts (including the screws fixing plastic light switches to the wall) may become 'live' under fault conditions if the earth conductor is disconnected, and it takes a lot less power to kill than it does to blow a 5 Amp fuse!

Thanks both. Not what I wanted to hear, but want to do the job properly. The floor in question is bare sanded and varnished floorboards screwed down onto the joists, so the wiring blocks will be accessible if necessary, but not exposed to casual meddling.

 

[Chivers7]

I can buy a 13amp connector with three connecting blocks to do this job if necessary.

Why not use a Distribution box buy a new piece of cable and rewire it from there? Should be fairly straight forward.

 

[TheLastMan]

a Distribution box.

Sorry, not sure what you mean by this. Googled it and just found socket extension leads!

 

[Chivers7]

perhaps i should have said junction http://www.tlc-direct.co.uk/Products/AAJB5.html

 

[TheLastMan]

That is not disimilar to what I bought, two terminals in, two terminals out - which is what initially confused me and why I assumed the earth was not needed.

What I actually got was one of these but with two connecting blocks rather than three.

Slighlty annoyed at B&Q at selling the connector as suitable for "5 amp lighting". It is now clear that the box was for wiring a lamp to a plug/socket rather than for inclusion in a fixed lighting circuit. Anyway, it was up to me to do my research properly, so ultimately it is my fault. Off to local hardware store now to see if I can pick up the necessary kit.

 

[Spark123]

The best option would be, if possible, to replace the whole length of cable from its terminations (i.e. between ceiling roses??). As has been said, a junction box should be accessable for inspection purposes.

 

[TheLastMan]

The best option would be, if possible, to replace the whole length of cable from its terminations (i.e. between ceiling roses??). As has been said, a junction box should be accessable for inspection purposes.

Agree this would be the best option, but we will be getting the house comprehensively rewired in a few months (when the bonus comes in!). Most of the sockets and switches seem to date from the 1970's, there aren't enough of them and the fuse box is positively ancient. We will be replacing the kitchen lights at that time so it can be done then - so just wanted a short stop-gap for the next few months.

Chatting to the guy in the hardware shop, it sounds like the piping causing the problem was probably galvanised steel conduit which carried the cable for the previous kitchen lights (which were replaced in about 1999). He says it is likely that more of the cabling in the house will be in this kind of conduit. Is that likely to be a problem?

Ironic that the only bit of modern cabling in the house was being chewed up by the remnants of the old cabling infrastructure!