Fault finding weird issue

Georgemidnight · Oct 24, 2023

Hi all,
Gone to look at a intermittent ground floor sockets fault today, the RCBO was tripping at random times with no pattern.

Nailed down a potential leg between 2 sockets ( 0.01 ohms on IR test) and temporarily replaced it to get the radial circuit (2.5mm on 20a B curve) to get it back on for the night.

Once replaced the circuit now stays on but trips when any item is plugged in (everything is out of the sockets beforeha

I’ve tested the RCD for nuisance tripping and X1 times which are okay. I’m running out of ideas here… okea

Marvo · Oct 24, 2023

If it wasn't tripping immediately a load is plugged in and it is now then it's obviously something to do with the wiring you've altered. I'd guess there's a contact between neutral and earth somewhere but honestly I'd suggest you just pay an electrician for an hour of his time to get it sorted out safely. The fact you've energised the circuit without fully testing it is worrying and likely to be dangerous....please just get a spsrky in to check it out.

Georgemidnight · Oct 24, 2023

Marvo said:
If it wasn't tripping immediately a load is plugged in and it is now then it's obviously something to do with the wiring you've altered. I'd guess there's a contact between neutral and earth somewhere but honestly I'd suggest you just pay an electrician for an hour of his time to get it sorted out safely. The fact you've energised the circuit without fully testing it is worrying and likely to be dangerous....please just get a spsrky in to check it out.

No, it stays livened up until any piece of equipment is plugged in.

I am a qualified electrician come here for advice.

timhoward · Oct 25, 2023

Georgemidnight said:
Nailed down a potential leg between 2 sockets ( 0.01 ohms on IR test) and temporarily replaced it to get the radial circuit (2.5mm on 20a B curve) to get it back on for the night.

Georgemidnight said:
Once replaced the circuit now stays on but trips when any item is plugged in

I'd go back to first principles. Are you now getting clear IR test results for the circuit at the CU?
Try L+N together to E, I'm suspecting you will see a N-E issue.

You could also try removing your new link and see what happens, i.e. is there another fault beyond the one you already found.

Rockingit · Oct 25, 2023

Georgemidnight said:
Hi all,
Gone to look at a intermittent ground floor sockets fault today, the RCBO was tripping at random times with no pattern.

Nailed down a potential leg between 2 sockets ( 0.01 ohms on IR test) and temporarily replaced it to get the radial circuit (2.5mm on 20a B curve) to get it back on for the night.

Once replaced the circuit now stays on but trips when any item is plugged in (everything is out of the sockets beforeha

I’ve tested the RCD for nuisance tripping and X1 times which are okay. I’m running out of ideas here… okea

OK - this isn’t a difficult circuit to fault find and just needs some patience and methodical analysis. You know the circuit and you know the outlets - so you know which is the last one. At 0.01Ohms you don’t have an IR issue - that’s basically a dead short (so see what you read on continuity). You either have an appliance plugged in still or you have cable damage. So work methodically along the circuit, removing each accessory as you go and testing the next leg of cable, and you will eventually discover either the mystery appliance or the damaged cable (or possibly a mis-wired socket). You can’t not - there’s nothing else left!! You might also then consider once you’ve put it all back together about replacing that RCBO as it will be ‘tired’ from so much tripping.

Rockingit · Oct 25, 2023

One other possibility does occur to me….. check if this circuit wasn’t originally part of a ring that got split because of some OTHER fault (the tell would be if you have two 20A radials on otherwise identical circuits) - that repair by a previous sparks could have been bodged and an interconnect between the two ‘new’ circuits could be left hidden.

buzzlightyear · Oct 25, 2023

Georgemidnight said:
No, it stays livened up until any piece of equipment is plugged in.

I am a qualified electrician come here for advice.

You need to start in the beginning on the fault, as above if ring split it and try to narrow it down. Possible either a appliance or N/E fault some where

oscar21 · Oct 25, 2023

Stupid question but you have put the neutral back into the RCBO and not the neutral bar, could be easilly done if you are under pressure to find the fault.

Ursanelec · Oct 25, 2023

Neutral and earth the wrong way around in the socket itself, had it quite a few times when replacing fuseboxes with rewireable fuses

Ursanelec · Oct 26, 2023

Or, I had this one yesterday on a floodlight fitted a number of years ago, by a family member of my customer, which never worked, it would trip the rcd as soon as you flick on the switch for it. I wonder why???

HappyHippyDad · Oct 26, 2023

update us @Georgemidnight when you discover the problem (even if it's something silly you've missed, we all make mistakes). We'd all be interested to know and it's mildly frustrating when you don't get closure.
What are your new IR results since you put your new leg in? Also, what are the IR results between (L-E, N-E or L and N combined to earth)?

Marvo · Oct 31, 2023

Georgemidnight said:
No, it stays livened up until any piece of equipment is plugged in.

I am a qualified electrician come here for advice.

Unlike an OCPD like an MCB, a residual current protective device won't trip even if there is a fault unless there's a load plugged in and some current flowing.

Fault finding weird issue

Georgemidnight

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Marvo

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Georgemidnight

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timhoward

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Rockingit

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Rockingit

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buzzlightyear

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oscar21

Ursanelec

Ursanelec

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HappyHippyDad

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Marvo

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