Bizarre RCD tripping fault

[PheonixFoX12]

Hi all,

Strange problem ive been trying to get my head around recently. I have an old single RCD protected Wylex fuse board in my property. Every time the loft space lights are turned on the RCD seems to trip out yet the loft space lights stay on for the duration.

However the only circuit not protected by the RCD are the downstairs lights or as so noted on the fuseboard.

Can anyone help.

Just to clarify I am a 2nd year apprentice with a Level 3 electrical install qualification.

Ta

 

[ProDave]

A N-E fault on a non RCD protected circuit can cause issues on an RCD protected circuit, e.g if there is some leakage on the RCD protected circuit but not enough to trip it, that leakage may increase as more neutral current is diverted when the other faulty circuit is on.

Proper methodical IR testing of all circuits will identify the problem.

 

[PheonixFoX12]

I understand. What I can't seem to understand is why the loft lighting continues to stay on when the RCD trips. Surely they would not be wired onto the downstairs lighting which is the only non-RCD protected circuit.

They are old fluorescent tubes, I was originally considering any in-rush current but this wouldnt affect the RCD more likely to affect the MCB protecting the circuit?

Cheers

 

[Murdoch]

If the light is on a mcb not protected by the rcd, then the light will stay on BUT a fault on this circuit could trip the rcd

be interested to see a photo of this board

 

[PheonixFoX12]

Agreed yes a fault on a non-rcd protected circuit could trip the RCD. What I find more bizarre is the location. Why do the lights in the loft stay on when the RCD trips purely because the only LTG circuit protected by the RCD is the downstairs circuit.

Here is a picture of the board if that helps. Apologies its a clipsal board not wylex.

 

[monkey5]

Is it on the alarm circuit? See which breaker actually turns the loft lights off.

 

[PheonixFoX12]

Not too sure that it's a good idea to switch off the alarm circuit as it's probably been put on the non-RCD protected side of the board for a reason.

However if you look closely the Alarm circuit and Upstairs Lighting circuits have been swapped at one point. Considering that might have something to do with this.

 

[Murdoch]

Ignore the labels. Turn on loft light and try turning off the breakers by the main switch one by one and you should find which circuit they are on

 

[monkey5]

At a guess the upstairs had been put on the other side as work done required it to be RCD protected, someone's decided alarm doesn't need RCD protection so swapped them. Turning the alarm breaker off isn't going to cause any problem just to see if the loft light is wired to it, not sure why you think it would. Alarm main panel possibly in loft and the light fed from that. Just a guess from what you've posted.

 

[PheonixFoX12]

Copy that, will report back with findings.

 

[PheonixFoX12]

At a guess the upstairs had been put on the other side as work done required it to be RCD protected, someone's decided alarm doesn't need RCD protection so swapped them. Turning the alarm breaker off isn't going to cause any problem just to see if the loft light is wired to it, not sure why you think it would. Alarm main panel possibly in loft and the light fed from that. Just a guess from what you've posted.

Perhaps what I was thinking too regarding the re-positioning of the circuits. Was also thinking that maybe they had been swapped to avoid having nuisance tripping issues on the RCD with the Alarm circuit. Just a theory anyway.

The Alarm panel is actually just next to this board.

 

[Murdoch]

Borrowed neutral ?

 

[PheonixFoX12]

Could well be

 

[Murdoch]

Could well be

your home or customers ?

 

[PheonixFoX12]

your home or customers ?

My own home mate

 

[Murdoch]

How long has the light been fitted?

 

[PheonixFoX12]

Several years, Wiring was altered in the loft area after access improvement was made to the area.

 

[binky]

Agreed yes a fault on a non-rcd protected circuit could trip the RCD. What I find more bizarre is the location. Why do the lights in the loft stay on when the RCD trips purely because the only LTG circuit protected by the RCD is the downstairs circuit.

Here is a picture of the board if that helps. Apologies its a clipsal board not wylex.

So whoever changed the board worked out there's a fault and moved the one circuit off the RCD.

 

[PheonixFoX12]

So whoever changed the board worked out there's a fault and moved the one circuit off the RCD.

Was thinking that yes.

 

[kerching]

Disconnect wir from loft light
Re try
Trips......not the light
Doesn't trip....probably the light
Fit a MKI lamp
Retry