RCD tripping issue on ring circuit

[Josh Kav]

First time poster go easy on me.

Got a call out to a job today, got told the RCD was tripping. Even when no appliances plugged in. And so it was intermittently about every 20 mins. Only two ring circuits on the RCD, on one of the rings im getting continuity across line and netural on both legs. Its not taking the MCB out, no fault across the earth.

Tested the RCD for nuisance tripping all passed fine.

Cant get my head around why with a permanent short the MCB wont trip? Going back tomorrow morning for further investigation and feeling as if i should suggest re wire of sockets due to reasonably low IR readings anyway.

Any thoughts would be appreciated.
Cheers

 

[SparkyChick]

Welcome to the forums.

When you say continuity... what kind of readings are you getting Line to Neutral? I'm suspecting they are not shorts but some appliance.

Why do I say that? Because a line/neutral fault won't trip the RCD because even under a direct short, the current flowing in line will be the same as that flowing in neutral and the RCD will quite happily sit there.

What IR readings were you getting?

 

[Josh Kav]

Cant remember the exact values on continuity, but it was a high level of resistance.

There are some kitchen appliances left to be checked, but those are on fused spurs so i suppose a fault could still come back up the netural if only single pole switch.

IR getting >0012 and i know its technically acceptable but its pretty low and makes me feel a bit uneasy.

 

[buzzlightyear]

possible damp .

 

[SparkyChick]

If you're getting continuity but a high resistance, then it's more like to be something plugged in/connected.

The IR reading is that L and N to earth, or L to earth, N to earth, L to N? And is that 1.2Mohms?

 

[Josh Kav]

L and N was 12 Mohms not 1.2 but thats all i can remember of the top of my head right now

 

[MJPD29]

Is there any chance there's an exterior light wired out the back of one of the sockets that might have damp in it? I've seen this happen many times

 

[buzzlightyear]

Is there any chance there's an exterior light wired out the back of one of the sockets that might have damp in it? I've seen this happen many times

damp post #4

 

[MJPD29]

I only ever read the post buzz, never the comments lol. For all I know I could constantly be repeating what others say

damp post #4

 

[dinger809]

What is the IR neutral to earth?

 

[123]

First time poster go easy on me.

Got a call out to a job today, got told the RCD was tripping. Even when no appliances plugged in. And so it was intermittently about every 20 mins. Only two ring circuits on the RCD, on one of the rings im getting continuity across line and netural on both legs. Its not taking the MCB out, no fault across the earth.

Tested the RCD for nuisance tripping all passed fine.

Cant get my head around why with a permanent short the MCB wont trip? Going back tomorrow morning for further investigation and feeling as if i should suggest re wire of sockets due to reasonably low IR readings anyway.

Any thoughts would be appreciated.
Cheers

Find the fault, fix the fault. Don't just go rewiring a circuit because there is a fault on it.
As the fault is still not found it could be literally anything, faulty appliance, central heating pump, damp, damaged cable and many more. Find where the fault is first, then come up with the solution.

 

[Wilko]

Hi Josh - Welcome to the Forum .

 

[Pete999]

Cant remember the exact values on continuity, but it was a high level of resistance.

There are some kitchen appliances left to be checked, but those are on fused spurs so i suppose a fault could still come back up the netural if only single pole switch.

IR getting >0012 and i know its technically acceptable but its pretty low and makes me feel a bit uneasy.

IR > 0012??

 

[Wilko]

Good Morning Pete !

 

[Pete999]

Good Morning Pete !

Morning Wilko

 

[littlespark]

I only ever read the post buzz, never the comments lol. For all I know I could constantly be repeating what others say.....


Appliance still plugged in. Cooker hood, FCU will be behind chimney.
Even turned off at socket, can still get an N-E fault to trip rcd.
Have you checked the mcb isn’t at fault?

Buy yourself a notepad and a pencil. For taking notes.

 

[DPG]

Could do with proper test results. Your information seems a bit vague.

 

[dksanders]

Is the heating fed by one of these circuits? If the RCD trips yet you've got good IR readings that implies an intermittent fault which can be caused by e.g. the heating/water heating coming on and there's a faulty component (pump, valve, boiler pcb, immersion element), or a compressor motor kicking in.

A healthy ring circuit has a natural earth leakage of about 3mA, the power supplies for modern equipment such as TVs, PCs, phone chargers etc also have quite high earth leakage; when it trips it could it be the sum of these exceeding 30mA.

Does it trip when you're there and have disconnected everything, or when stuffs plugged in/switched on?

Is there e.g. a PIR external light fed via a FCU on the circuit?