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

[saveasteading]

19 hours ago, FuerteStu said:

If its recent,

No It's been ok for 30 years....and nowhere near my recent overflowing header tank (resolved 3 weeks ago anyway). Also nobody has been near that area.

 

19 hours ago, FuerteStu said:

Moisture inside the switch, or fitting. 

The switch is well clear of any water source....the fitting I will check when I venture up. Tomorrow is always a good day for unpleasant things.

 

 

20 hours ago, FuerteStu said:

the lamp itself causing the trip.

Removed without benefit.

 

20 hours ago, andyscotland said:

to be sure I've understood: 

correct It is 30A.

 

20 hours ago, andyscotland said:

t's common for electronics (computers, LED drivers, smart stuff) to produce a small level of background leakage due to the way electronic transformers work.

As 4 family members have just left along with many chargers,  I've checked again but it still trips. Anyway, they would be on the sockets ring main not the lighting circuit.

 

Much confused though as 2 switches tripped at the same time. Isn't that like a rope or chain snapping in 2 places? surely one part breaks and the other doesn't?

DB3 the left switch, along with the red switch on the distribution board (or am I misremembering already and it was the adjacent black? )

 

I put some special food in the attic a week ago, and then more. There was scampering until 2 days ago.  There is no smell of rotting rodents but they may have gone elsewhere to be tidy. Mice smell 3 days, rats 5 days.

 

So tomorrow I will put on my new favourite wooly hat with lamp in front (highly recommended) and get up there. I believe I am checking the ceiling connection for damp or dead things, and the cable from light fitting to switch, looking for teeth marks????

[andyscotland]

38 minutes ago, saveasteading said:

 

correct It is 30A.

30 milliAmps I assume.

 

 

38 minutes ago, saveasteading said:

As 4 family members have just left along with many chargers,  I've checked again but it still trips. Anyway, they would be on the sockets ring main not the lighting circuit.

 

The thing is the RCD is across both the sockets and the lights so that would not necessarily matter. But if still tripping then sounds like that's not a factor.

38 minutes ago, saveasteading said:

 

Much confused though as 2 switches tripped at the same time. Isn't that like a rope or chain snapping in 2 places? surely one part breaks and the other doesn't?

DB3 the left switch, along with the red switch on the distribution board (or am I misremembering already and it was the adjacent black? )

 

The red switch is just a switch so it won't have been that. If it was caused by the light it should have been the RCD (the black one with a test button) on the right  of the board e.g. furthest from the red switch as that is the one that protects the half of the board with your lighting circuit breaker (the one that is switched off).

 

It is possible for 2 RCDs to trip simultaneously - the tripping current and time are both so low that they trip easily and fast. Opening the circuit is a mechanical action so it's rapid but not instant. So the downstream can detect a fault and start opening but the power remains connected for enough milliseconds that the upstream also sees the fault.

 

Ideally an installation would be designed to reduce the risk of this happening but it's not always possible (and even with the best designs can't be guaranteed in all circumstances).

 

38 minutes ago, saveasteading said:

 

I put some special food in the attic a week ago, and then more. There was scampering until 2 days ago.  There is no smell of rotting rodents but they may have gone elsewhere to be tidy. Mice smell 3 days, rats 5 days.

 

So tomorrow I will put on my new favourite wooly hat with lamp in front (highly recommended) and get up there. I believe I am checking the ceiling connection for damp or dead things, and the cable from light fitting to switch, looking for teeth marks????

 

Depending how your lighting is wired, I would also check any cable from the suspect lamp to the next fitting. And also look out for any junction boxes nearby and similarly check them for dead things/damp/visible damage.

 

Make sure you de-energise the circuit at the distribution board before you start poking around, especially as there is a chance of damaged/wet connections. And if there is anyone else home who might be tempted to turn circuit breakers on, tell them what you're doing.

[Onoff]

52 minutes ago, saveasteading said:

So tomorrow I will put on my new favourite wooly hat with lamp in front (highly recommended) and get up there. I believe I am checking the ceiling connection for damp or dead things, and the cable from light fitting to switch, looking for teeth marks????

 

For example:

 

 

 

Also junction boxes that haven't had the lids put on properly and have open cable entries. Mice can get through a hole the size of a pencil. You can get slugs, wasps etc in there too. 

[BotusBuild]

On 19/12/2024 at 19:59, Mattg4321 said:

Only if there was a fault between the switch and an earthed back box could it cause tripping.

 

On 19/12/2024 at 19:59, Mattg4321 said:

unless subjected to very high loads or extreme temperatures etc.

 

On 19/12/2024 at 19:59, Mattg4321 said:

If in a domestic property it’s unknown how long it will last in good conditions as the earliest examples from the 60’s are still in good condition.

So, in all the quoted examples above, there is a possibility, however low that might be. Ergo, these things should be tested for. And that testing can be carried out without specialist equipment.

Regarding the last point, I bought a 1980's built property in 1997 and had to have about 25% of the wiring replaced as the cable had hardened and cracked. Sometimes, you get shit materials and knowing the quality of the rest of the property I can believe this builder was get stuff from wherever they could as cheap as they could.

🫳🎤

[saveasteading]

52 minutes ago, andyscotland said:

should have been the RCD (the black one with a test button) on the right  of the board e.g. furthest from the red switch

Memory failed on the colour, but it was that side so was the left hand black one.

 

The switch to the right that is off may be confusing things  (The one  with the tag against it)  It is another matter altogether. An outside light circuit that pings in wet conditions. so it is turned off.

 

50 minutes ago, Onoff said:

For example:

Helpful. I would be looking for such, but why would that short?  Exposed wire but the top one is not touching or near any other conductor??

 

 

 

 

[Onoff]

15 minutes ago, saveasteading said:

The switch to the right that is off may be confusing things  (The one  with the tag against it)  It is another matter altogether. An outside light circuit that pings in wet conditions. so it is turned off.

 

That's a possibility. If the outside light fitting is wet you could be getting a neutral to earth fault irrespective of whether that breaker is switched off. 

 

Might be worth isolating that "wet" light altogether. 

[Mattg4321]

4 hours ago, BotusBuild said:

 

 

So, in all the quoted examples above, there is a possibility, however low that might be. Ergo, these things should be tested for. And that testing can be carried out without specialist equipment.

Regarding the last point, I bought a 1980's built property in 1997 and had to have about 25% of the wiring replaced as the cable had hardened and cracked. Sometimes, you get shit materials and knowing the quality of the rest of the property I can believe this builder was get stuff from wherever they could as cheap as they could.

🫳🎤

Depends if you like wasting your time or not I suppose. 
 

Chances of it being any of those things mentioned are pretty slim. I like to target the most likely thing first, before clutching at straws, but have already given advice earlier in the thread, that has been repeated by someone else on here.
 

Getting up in the loft with the circuit disconnected and inspecting the installation is free and requires no insulation resistance tester. 
 

However, it’s probably still best to get hold of some proper test equipment or an electrician as ‘bang testing’ isn’t really something to be advised. 

[andyscotland]

15 hours ago, saveasteading said:

Memory failed on the colour, but it was that side so was the left hand black one.

 

The switch to the right that is off may be confusing things  (The one  with the tag against it)  It is another matter altogether. An outside light circuit that pings in wet conditions. so it is turned off.

 

Ah, I'd misunderstood the original pic. So I assume the circuit that feeds the suspect light is also on the left hand half of the board? That would make sense.

 

15 hours ago, saveasteading said:

Helpful. I would be looking for such, but why would that short?  Exposed wire but the top one is not touching or near any other conductor??

Top one would be fairly unlikely to be causing this type of fault (but should obviously still be fixed, for safety). Bottom one would be a candidate as there is a copper pipe nearby and if the exposed neutral contacted that (or was bridged to it by moisture) that would be exactly the type of trip you're getting.

 

15 hours ago, Onoff said:

That's a possibility. If the outside light fitting is wet you could be getting a neutral to earth fault irrespective of whether that breaker is switched off. 

 

Might be worth isolating that "wet" light altogether. 

 

Worth checking, but equally if we have now established that's on the other half of the board to the RCD that tripped then it is probably not the culprit in this case.

[G and J]

I’m worried.  How long do we wait for @saveasteading to escape from the rodent ruled attic before someone brave and foolhardy dons a head torch to go in after them?

[saveasteading]

28 minutes ago, G and J said:

How long do we wait

I've thought (and been reminded) of  10 other things I have to do first.

Finish 'wordle and connections', compost heap, visit the big project, get cat food.....

[ProDave]

Ah one of those "what a shame something more important has come along" jobs.

 

My BIL lives in a 300 year old Welsh farmhouse with bats and squirrels in the loft. On the few occasions he ventures up there he does so in a disposable boiler suit and mask.

[G and J]

44 minutes ago, saveasteading said:

I've thought (and been reminded) of  10 other things I have to do first.

Finish 'wordle and connections', compost heap, visit the big project, get cat food.....

It’s a it like a café loyalty card.  Amass enough ‘oh I must just…..’ things and the arc welded mouse will dry up and stop it tripping.

 

Think of it as putting the cute into electrocuted….

[G and J]

26 minutes ago, ProDave said:

Ah one of those "what a shame something more important has come along" jobs.

 

My BIL lives in a 300 year old Welsh farmhouse with bats and squirrels in the loft. On the few occasions he ventures up there he does so in a disposable boiler suit and mask.

I fear squirrel incursion significantly more than I fear mouse or rat attack.  Time to go sit in my garage cuddling my air rifle while trying to regulate my breathing….

[Onoff]

Just now, G and J said:

I fear squirrel incursion significantly more than I fear mouse or rat attack.  Time to go sit in my garage cuddling my air rifle while trying to regulate my breathing….

 

Yes, I really need to get rid of my overhead power supply to the house one day! 

[G and J]

1 hour ago, Onoff said:

 

Yes, I really need to get rid of my overhead power supply to the house one day! 

We aren’t talking about that.  We have to go UG and it’s costing us best part of £10k to get lecky from a pole that is 6m from our boundary.  All while working under other peeps power feed that won’t be moving any time soon. 

[SteamyTea]

5 hours ago, G and J said:

putting the cute into electrocute

Who took the fizz out of physics.

Probably someone from Scunthorpe.

Edited yesterday at 17:08 by SteamyTea

[saveasteading]

I've done it. I fought through the cobwebs like Prince Charming, but the good news is the absence of clutter in that remote corner.

 

There is rodent damage. Also a strange brown crud on the cables there.

on the first photo we see both the lamp and switch cables. They run to a large connection box.

 

The black wire is exposed over about 30mm but does not look to be nibbled itself. There are some more mouse nibbles near, to the left,  but very shallow.

I actually see more clearly on the photo than I could up close, but should have snapped it further back to get the focus better. The near, out of focus, bit looks worse than it did in real time.

I'm thinking the brown stain might be wood resin dripping from above, perhaps in summer heat or from occasional leaks. Thus attracting nibbling. Then that water now gets into the cable?

There was no sign of dampness but it has been very wet and windy and this is under the ridge and one drop might do it....or some of that resin has built up inside.

 

I'd have thought that I'd have to see copper for any short but I don't know.

 

No dead things. Lots of historic mouse (and some rat) droppings But the second dose of bait is untouched so there weren't many around.

 

I didn't look in the connection box. Well, I lifted a loose corner and nothing was apparent.

 

The cables simply drop through the lath and plaster ceiling. Nothing dead visible in the holes.

 

The grey cables are long redundant.

 

I'm guessing and welcome any expert or other input.

 

 

 

[SteamyTea]

10 minutes ago, saveasteading said:

I've done it.

So how you going to fix it?

[saveasteading]

1 hour ago, SteamyTea said:

So how you going to fix it?

I'm hoping that someone is going to say, yes that's obviously causing the issue. Or otherwise.

And why this shorts when only one core seems to be damaged.

Then I'm thinking I replace that portion of cable, preferably without taking down the lamp fitting because....it all makes work....

Can I sensibly cut out 1m and join with a box or a connector each end?  I know one electrician who refuses to use sometimes, especially the push fit type.

 

[SteamyTea]

I think you can use WAGO connectors as a permanent fix, ask @ProDave as he knows what he is doing up your way.

 

22 minutes ago, saveasteading said:

And why this shorts when only one core seems to be damaged.

Who knows, electricity is a quantum phenomena, so all sorts of magic is happening.

There may be another problem that has been masked by this small amount of damage i.e. shared neutrals, but you need to change that bit of cable anyway, so nothing lost really.

[saveasteading]

25 minutes ago, SteamyTea said:

he knows what he is doing up your way.

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

 

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.

Edited 23 hours ago by saveasteading

[G and J]

48 minutes ago, saveasteading said:

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

 

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.

Ummm, I’m assuming it’s still tripping out?  If so, which switch?

[G and J]

3 minutes ago, G and J said:

Ummm, I’m assuming it’s still tripping out?  If so, which switch?

PS, you might want to try it a few times to ensure consistency. 

[FuerteStu]

It's possible that's enough damage to the cable to trigger nuisance tripping. 

 

The only way to be sure is to isolate the cable and see if the problem persists.. But it could just mean you're isolating the problem that's further upstream. It's a multiple test scenario. 

 

There was a stage when the grey pvc on twin and earth broke down and left an oily residue. I think they changed the formula.

 

It was rather tasty to our rodent friends, I've seen them strip off metre long sections, leaving only the inner cores. 

 

It doesn't take much removal to trip an rcd if there is moisture in the air, opening a section allows capillary action to trigger conductivity through what can barely be seen. If it was in the live it would just vapourise the water, but the neutral to earth allows an alternative path and the rcd doesn't like that. 

 

My suggestion, replace.. And see if it's still a problem, then investigate further. 

[saveasteading]

1 hour ago, FuerteStu said:

My suggestion, replace..

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.

2 hours ago, G and J said:

try it a few times

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