One light circuit is tripping the system. what to look for?

[G and J]

8 minutes ago, saveasteading said:

Yes that's the plan. I was hoping for such an obvious bit of damage so it's good news. I need advice now on an acceptable way of patching in a repair, eg the boxes.

They seem appropriate to me as I can fix them to the joist to avoid any trailing cable.

I did, including after the visitors left, taking multiple chargers with them.

 

 

So it still trips even after your dangerous escapade!  Which switch goes?

[joe90]

Why not cut out say 100mm of that damaged cable and temporarily connect using a junction box (you seem to have slack if you cut the corner) if the tripping still occurs you have proved this damage was not causing the problem. 

[andyscotland]

3 hours ago, saveasteading said:

I'm down this way, nearly France, but electricicles behave the same.

 

I guess maybe @SteamyTea was thinking regs might be different, but this is just BS7671 which applies UK wide (not France though 🤣).

 

3 hours ago, saveasteading said:

Good reminder. It was Wagos that the electrician didn't like. I had done cabling on another daughters old house and asked him to do the final connections but he replaced them all.

I will take advice from @ProDaveor  other experts if they would please advise.

 

I'm not sure why the electrician didn't like Wagos if they were in a proper containment (other than that some people don't like new things).

 

When installed per manufacturer's instructions in a wagobox they are certified for use even in a totally inaccessible location (unlike anything with screw terminals). And are very hard to get wrong (again unlike anything with screw terminals). They do need to be in a proper box to provide protection for the unsheathed cables and strain relief, among other things, and the cable tie to hold the box closed is also important.

 

I would definitely use a wagobox to repair that damaged section, ultimately even if it's not the cause - and it could well be - it needs to be repaired anyway.

 

Hard to see from the photos how far it is to the junction box, if it's not too far best/cheapest bet is probably just one wagobox and then replace the whole section to the junction box. Alternatively get 2 boxes and just splice in a short replacement section. Make sure the cable you use matches or exceeds the size of the existing (I'd assume 1.5mm² will be fine, but check).

 

Unless you have a spare bit of suitable old cable lying around for the repair you are going to have different core colours in the replacement section. Old red = Brown, Old black = Blue. You should therefore also have a label like this at the origin (you can make your own) - not that there's really any electricians out there who aren't well aware of the harmonised colours by now!

 

Technically speaking as this is a repair to the fixed wiring it is Minor Electrical Works and should be done by a competent person, properly tested (with calibrated test equipment) & documented.

[G and J]

How I’d attack it would be set by whether it’s the RCD or MCB that’s tripping. 
 

Either way might be time for a kinetic type switch. 

[FuerteStu]

1 minute ago, G and J said:

How I’d attack it would be set by whether it’s the RCD or MCB that’s tripping. 

Yep. 

 

And if it's an rcbo, the way it trips.. A pop or bang. 

 

Is it live to earth, or neutral to earth

[G and J]

I think @saveasteadingsaid it happens even when the bulb is removed, and I would assume the switch is in the live side, so it is highly likely to be the returning switched live to earth (I think it’s most likely to be within one cable rather than between cables). 
 

But assumptions are dangerous things when dealing with stuff put in years ago by unknown dudes. 

[FuerteStu]

5 minutes ago, G and J said:

I think @saveasteadingsaid it happens even when the bulb is removed, and I would assume the switch is in the live side, so it is highly likely to be the returning switched live to earth (I think it’s most likely to be within one cable rather than between cables). 
 

But assumptions are dangerous things when dealing with stuff put in years ago by unknown dudes. 

Unless there is no other load on that circuit. 

It could be neutral to earth, but without load the rcd doesn't trip as there is nothing to imbalance

[Onoff]

You might find this interesting. Some of that old twin and earth with the white sheath just seems to crumble

 

https://electrical.theiet.org/wiring-matters/years/2021/84-march-2021/estimating-the-age-of-an-electrical-installation/

 

A discussion too on here from years back:

 

 

[saveasteading]

I'm going shopping apparently. 

I'll read all that clever stuff later....thanks all.