House Electrics

Consumer unit.jpg


One for the electrical experts.

I have a pair of wall lights in my lounge and sometimes when I turn them off, the power goes off. As you can see, in the consumer unit there are 2 RCDs each controlling 5 individual trips. When the problem occurs, it is the right hand RCD that has dropped down. The trip immediately to the right of it is the one for the downstairs lights, but it remains up.

I had thought that perhaps the switch was arcing a bit when it opens, so I replaced it but it made no difference. I would have thought that the light circuit trip should go first, not the RCD. Is the RCD too sensitive?

An electrician who I talked to said it made no sense and could offer no suggestions.
 
The RCD and the light circuit trip are doing two different things. The "trip" as everyone calls it is a simple overcurrent device. It should only really go if there's a serious fault on the line drawing more current than the rating of the breaker, or if there are just too many things running off that circuit. They can also go if something draws a large startup current like a motor.

The RCD is looking at the current flowing into the live wire and comparing it to the current coming back through the neutral. If there's a difference, current must be leaking out somewhere so it shuts off the circuit. It is usually set to detect a tiny imbalance in the order of milliamps. A qualified electrician will be able to tell you how "insensitive" you are allowed to make it - which I am not.

It's very strange that it happens when you turn the lights off. Is it a simple on-off switch or is it a setup where you have two switches in different places controlling the same light? Are they ordinary 240V bulbs or are they spotlight type lights with a power supply box mounted in the ceiling?
 

robcollins

Member
Location
Wicklow
Is there any particular pattern to when it trips? Perhaps wet weather?

What sort of lamps are in the fittings?

Are they incandescent or LED or energy savers?

Did you inspect the fitting for any signs of heating or damage?

Have you checked the connections to each fitting?

I’ve seen energy saving CFL lamps trip RCDs before. You’ll just have to go through it piece by piece.

That’s the list I’d work from if I was looking for the fault. I wouldn’t throw out the RCD just yet.

Have you a photo of the fittings in question?
 

towbar

Member
Location
Louth, Ireland
Is there any particular pattern to when it trips? Perhaps wet weather?

What sort of lamps are in the fittings?

Are they incandescent or LED or energy savers?

Did you inspect the fitting for any signs of heating or damage?

Have you checked the connections to each fitting?

I’ve seen energy saving CFL lamps trip RCDs before. You’ll just have to go through it piece by piece.

That’s the list I’d work from if I was looking for the fault. I wouldn’t throw out the RCD just yet.

Have you a photo of the fittings in question?
check for loose connections in switch or light fitting sometimes arcing in switch can cause an rcd to trip
 

milkloss

Member
Livestock Farmer
Location
East Sussex
Spoke to a buddy today. He said that some cfl fittings can cause a phase shift and or earth leakage that is enough to trip a 30ma rcd. I think that’s the message anyway and there’s a link to similar on iet forums when I googled it to try and make sense of it myself.

Recommend to change the light fitting inc starter and ballast for a new quality make
 

TheTallGuy

Member
Location
Cambridgeshire
My guess is that during switch off the ballast is generating a high voltage spike that is going to "earth" either through the ballast/light fitting or through the wiring. A spark worth his salt should know about that sort of thing & would be doing an insulation test to check the wiring.
 

Ukjay

Member
Location
Wales!
Firstly - has this just started - if so what have you changed?

If not - check the light switch to see if it is a two way switch, it may be wired into the wrong - ie, is the live coming in on the 2 way circuit, and the light fitting then being supplied from the L1 / L2 on the switch being fed by a common, as this can cause the tripping due to the neutral / earth trip? (this is what I was told when I managed to wire up a switch wrong and sparkie fixed it)..

IF that is not the case, then either the switch or fitting would be changed in my house..
 
It hasn't just started, it's being going on for several years. It'll go for months and not do it, sometimes once or twice a week. There is no other switch. I changed the switch a couple of years ago..
 

Ukjay

Member
Location
Wales!
It hasn't just started, it's being going on for several years. It'll go for months and not do it, sometimes once or twice a week. There is no other switch. I changed the switch a couple of years ago..

OK, so the time of you changing switch to the problem appear similar, so is your switch a single gang 2 way switch (Does it have Com L1 L2) that you could have the wires incorrectly fitted as I mistakenly did on one of mine by using L2?

Is yours wired Common and L1?

Oh, and how old is your fitting (Light) is it as old?
 

towbar

Member
Location
Louth, Ireland
OK, so the time of you changing switch to the problem appear similar, so is your switch a single gang 2 way switch (Does it have Com L1 L2) that you could have the wires incorrectly fitted as I mistakenly did on one of mine by using L2?

Is yours wired Common and L1?

Oh, and how old is your fitting (Light) is it as old?
I'm curious how the switch wiring if there is no neutral in the switch could cause it?
 

Ukjay

Member
Location
Wales!
I'm curious how the switch wiring if there is no neutral in the switch could cause it?

What he said to me was that due to how I had wired the switch (common and live round the wrong way and in wrong terminal) it went out on earth fault.

He swapped it and to date no issue, so can only assume he was correct.
 
I don't want to change the fittings and shades, but I think that I'll convert them to leds. I take it that it's just a matter of junking the ballasts and replacing the cfl bulb holders with ordinary ones.
 

robcollins

Member
Location
Wicklow
When I was an apprentice we were told the high arcs that are required to start fluorescent fittings can cause an RCD to trip.

That’s why we didn’t have the lights on an RCD, simply a 10A MCB.

When I’m doing a rewire nowadays I use RCBOs instead of MCBs and RCDs.

Swapping to normal lamp holders and a quick check of the wiring should solve the problem.

If you’re after energy saving lamps, LED are great. I use the ones from IKEA myself, as they’re a good price and quality.
 

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