Strange RCD Problem

[EWebster]

Afternoon all.

I've got a problem with an RCD tripping that I can't get my head round.

Upstairs lights are tripping the RCD. I switch off the MCB, but still tripping. So you'd think it was an earth/neutral fault. Nope. I remove the earth and the neutral from the board, and it trips on Live only. Very strange.

>299 ohms IR on all configurations (L/E, L/N, E/N), so no shorts.

Borrowed neutral? Nope. I wired the house 2 years ago. All been fine until last week. Also, putting the circuit on the other side of the board doesn't solve it.

Faulty RCD? Nope. Tests fine, and tried another new one just to make sure.

Anyone got any ideas?


Best regards,

E

 

[Pete999]

Not being funny mate how do you deduce it's the upstairs lighting that tripping your RCD

 

[EWebster]

Disconnected everything but the upstairs lights. Also put them through their own RCBO, and pops every time.

 

[GLENNSPARK]

Afternoon all.

I've got a problem with an RCD tripping that I can't get my head round.

Upstairs lights are tripping the RCD. I switch off the MCB, but still tripping. So you'd think it was an earth/neutral fault. Nope. I remove the earth and the neutral from the board, and it trips on Live only. Very strange.

>299 ohms IR on all configurations (L/E, L/N, E/N), so no shorts.

Borrowed neutral? Nope. I wired the house 2 years ago. All been fine until last week. Also, putting the circuit on the other side of the board doesn't solve it.

Faulty RCD? Nope. Tests fine, and tried another new one just to make sure.

Anyone got any ideas?


Best regards,

E

whats the earthing arrangements?

 

[Pete999]

Just getting my head around your problem, you have disconnected Line Neutral and cpc of the upstairs lighting, you may have a shared neutral via the landing light

 

[skydog23]

Although you wired the house yourself 2 years ago, people are strange things and do all sorts of things when your not there.
Have they been doing anything they shouldn't have? Put up any new light fittings ?
Put a light in the attic ?
Been doing any drilling/ screwing lately.
I'm just thinking of something penetration and putting a fault somewhere
Or even been a bit shabby with a class 1 fitting and some neutral touching earth.
Just a thought.

 

[EWebster]

Several answers:

Earthing is TT.
No work done on the electrics by the owner. I've checked everywhere and can't see any nails etc, and as I mentioned, IR is clear as a bell, so no shorts.
RCD trips when circuit on either side of the board. No shared neutral apparent.
RCD trips when Earth/Neutral are out of the board, but line is connected and live. Come of think of it, is that normal state?

 

[Octopus]

Dare I suggest calling in a competent sparky? Your ideas seem very hit and miss.

 

[ImpededLoop]

Line to earth fault? Trips when line is connected and finds a path to earth through hallway switch which has cpc's from two circuits terminated inside it....

 

[Silly Sausage]

Disconnected everything but the upstairs lights. Also put them through their own RCBO, and pops every time.

Just to be clear here, with the circuit N & E disconnected and L in this RCBO, and the board energized; are you saying you can't reset the RCBO?

Have you tried IR testing between L and the N & E bars in the board, with circuit N & E disconnected?

 

[Octopus]

You need to do R1 + R2's at each light with the switch on to see if you have continuity.

I fixed a problem last year where the mice had eaten their way through both layers of insulation AND the copper - and it was the switch drop at fault!

 

[EWebster]

Dare I suggest calling in a competent sparky? Your ideas seem very hit and miss.

Helpful. Thanks Murdoch!

Not.

 

[EWebster]

Line to earth fault? Trips when line is connected and finds a path to earth through hallway switch which has cpc's from two circuits terminated inside it....

That occurred to me too. I removed the switch and cleared the wires to make sure.

I'll start dismantling the circuit bit by bit and testing. Luckily there is loft access to most of the circuit. Thought I'd ask and see if anyone had any helpful advice though, as it's not a problem I've come across before.

One other thing I forgot to mention - When the circuit is in place and NOT tripping (happens occasionally as it is an intermittent fault), the RCD will not trip when tested. I can get over 500mA through it from my Megger and not trip.

 

[telectrix]

neutral fault can cause this. had it before.

 

[foresite123]

Have you carried out your insulation resistance tests with the cpc connected to the means of earthing.

Your line conductor may be shorting to a piece of earth metalwork.

 

[EWebster]

Have you carried out your insulation resistance tests with the cpc connected to the means of earthing.

Your line conductor may be shorting to a piece of earth metalwork.

Many thanks Foresite. I'll give that a go. A very helpful suggestion, unlike some others who should know better on this forum.

Best regards,

E.

 

[Deleted member 9648]

Have you carried out your insulation resistance tests with the cpc connected to the means of earthing.

Your line conductor may be shorting to a piece of earth metalwork.

Many thanks Foresite. I'll give that a go. A very helpful suggestion, unlike some others who should know better on this forum.

Best regards,

E.

I would have thought that was pretty obvious.If you have disconnected the N and E and it still trips there must be a path for current to flow to cause an imbalance. Logical.
I'ts another 'RCD trips but it's all connected properly and all tests are fine and and the RCD has been replaced' thread.......well in that case it wont trip then!

 

[Octopus]

Many thanks Foresite. I'll give that a go. A very helpful suggestion, unlike some others who should know better on this forum.

Best regards,

E.

Stated by a member of 4.5 years and a mere 57 posts!

 

[telectrix]

it's as many as heinz, though.if only carlsberg made RCDs. lol.

 

[MDJ]

Afternoon all.

I've got a problem with an RCD tripping that I can't get my head round.

Upstairs lights are tripping the RCD. I switch off the MCB, but still tripping. So you'd think it was an earth/neutral fault. Nope. I remove the earth and the neutral from the board, and it trips on Live only. Very strange.

>299 ohms IR on all configurations (L/E, L/N, E/N), so no shorts.

Borrowed neutral? Nope. I wired the house 2 years ago. All been fine until last week. Also, putting the circuit on the other side of the board doesn't solve it.

Faulty RCD? Nope. Tests fine, and tried another new one just to make sure.

Anyone got any ideas?


Best regards,

E

Must be a link from the earth on the upstairs circuit to an earth on another circuit, and there is a live or neutral to earth fault, if there is a switch on and light bulbs in lights then as there is an earth linked somewhere you will get a neutral or live to earth fault. Basic school boy testing is required now, all lamps out, all switches on, test between all cores and go from there.