Fixing pinched light cable

[Tegid Owen]

Good evening,

The upstairs lights have tripped a not coming back on. I was in the attic at the time and thought it may be caused by a pinched cable under floor. I have raised a section of the floor (the one recently installed) and saw that there was a pinched wire (you may be able to see from the photo). To repair this problem I plan to cut the damaged section of cable and fit junction boxes (2 boxes as the cable is tight and has little slack) to reconnect the cable. You may be able to see the junction boxes I plan to use in the photo. My question is, is this a safe and effective way of fixing the problem? Many thanks in advance

 

[terryplumb]

How do you know that cable ,which doesn't appear to have damaged insulation, is the cause of your problem ?
What exactly has tripped , MCB,RCD,RCBO ??

 

[robinbanks]

I'd expect it more likely that a screw/nail has been driven through a wire, or a wire has been flattened by something that really damaged the sheath (such as ramming it into the gang nail strip of a roof truss) and bridged the connectors, but terry's question is a good one; show us a picture of the consumer unit and point out which thing has tripped (if it's not obvious)

Your debox connectors boxes aren't suitable for making connections in inaccessible places, in my opinion. I'd seek something maintenance free instead

 

[terryplumb]

Your debox connectors boxes aren't suitable for making connections in inaccessible places, in my opinion. I'd seek something maintenance free instead

The one in the pic isnt maintenance free. ,But they do one that is ,I think !

 

[SUNRAY]

I'd be looking to replace the length of cable rather than adding 2 junction boxes, that is of course after isolating the existing piece and prooving it is the fault.

 

[Tegid Owen]

How do you know that cable ,which doesn't appear to have damaged insulation, is the cause of your problem ?
What exactly has tripped , MCB,RCD,RCBO ??

I don't know for sure that its the trapped cable however, this seems the most likely as I've recently installed a section of flooring on top of this cable. I was very careful and no screws were anywhere near any of the cables. I've been walking a bit on this section of flooring today too. From what I gather on this circuit there are 4 upstairs lights and one socket (all are not working as its isolated at the moment). Everything else is working i.e all other upstairs sockets.

 

[Tegid Owen]

The one in the pic isnt maintenance free. ,But they do one that is ,I think !

What do you both mean by maintenance free?

 

[terryplumb]

Maintenance free junction boxes have terminals that allow the conductor to be held in place by spring pressure ,rather than screw down . They also require strain relief on the cables ,so they can't be pulled out easily.
Is there an external light on the circuit ?
What is plugged into the socket ?

 

[Tegid Owen]

Maintenance free junction boxes have terminals that allow the conductor to be held in place by spring pressure ,rather than screw down . They also require strain relief on the cables ,so they can't be pulled out easily.
Is there an external light on the circuit ?
What is plugged into the socket ?

Ah I see now what you mean about maintenance free. There is no outside light, hasn't been since I moved in around 7 years ago. At the time it first tripped there was an extension lead and a lamp plugged into the socket. The socket is on the wall at the bottom of the attic ladder. I have unplugged this and tried the trip switch again but it still trips.

 

[terryplumb]

At exactly what point did the MCB trip ? When a light switch was turned on ? Whilst you were walking around on the floor above the cable ? Some other coincidence ?

 

[Tegid Owen]

At exactly what point did the MCB trip ? When a light switch was turned on ? Whilst you were walking around on the floor above the cable ? Some other coincidence ?

I was up in the attic walking around at the time. The light had been on for a good 15 minutes. I wasn't anywhere near any switches or cables. Only the ones under the flooring

 

[terryplumb]

You could replace the cable / effect a temporary repair ,see if that solves the issue. It doesn't appear too badly damaged in my opinion ,and I suspect the problem may be elsewhere.
Were you standing in the position of that cable when MCB tripped ?

 

[terryplumb]

How do you know that damaged cable is even on the same circuit as the tripped MCB ??

 

[Tegid Owen]

You could replace the cable / effect a temporary repair ,see if that solves the issue. It doesn't appear too badly damaged in my opinion ,and I suspect the problem may be elsewhere.
Were you standing in the position of that cable when MCB tripped ?

I was standing close to it but not directly above. You're right, the only way to find out is to a temporary repair to see if this cable is the problem. There is no tear to be seen on the cable, not on the outside anyway. It may be damaged inside? Ideally I would like to isolate this part of the cable specifically. There are 4 upstairs light and the pinched cable is closest to the landing light. I don't know if this comes directly from downstairs or does it go through the other lights first. Difficult to find out without lifting up most of the attic flooring

 

[Tegid Owen]

How do you know that damaged cable is even on the same circuit as the tripped MCB ??

Yes, evrything else in the house works even the upstairs sockets (apart from one at the bottom of the attic ladder). I presume this is on the same circuit as all the lights