can anyone help??

[VoltzElectrical]

I went to a house over christmas where the RCD covering the whole installation kept tripping.

I get there and the guy tells me it all started after he changed his outside lights. He's taken them down and taped everything up losing any markings.

The circuit is off. I switch it on. No problem. Then it starts to rain so I just take a look at the fittings he wants put up. He wants to override the sensor with a switch inside, thats the way it is wired. There was no facility on the fitting for this so he said ok, I'll change the fittings and you can comeback and fit them. I go.

I go back on saturday and its dry so I bell out the cables to find what is what and put the fittings up, plenty of silicone, turn it on all working, happy days.

Get a text today, lighting circuit intermittently tripping the RCD. Now I thought the original problem was moisture ingress in the fittings the guy put up himself. On one exposed wall their was quite a lot of corrosion on the fitting screws. Now the problem is still there after I have put new fittings up properly and it hasn't rained!

I'm gonna go tomorrow and IR test the circuit, and ramp test the RCD, But do any of you have any suggestions of what to do, or look for for intermittent RCD tripping on a lighting circuit?

 

[GLENNSPARK]

well water ingress would be a common cause here as i think you already know.....but theres always the trapped cable n all....it could be some residual moisture in the cable ends from the last set of lights....as you say ..ramp the RCD and IR this lighting circuit.....i mean, are you sure its the lighting thats causing this intermittent tripping?....could be that the cables feeding this are joint boxed under the floor and its something there.....could be a loose neutral n all......

 

[VoltzElectrical]

it's not water ingress in the outside lights for sure. I fitted them on a bone dry sunny day and it hasn't rained since. I'm guessing its wired using the JB method as i took down the hall light and there was only one cable, but I suppose it could be 3 plated at the landing light or I hope the JB is in the attic as the house has tongue and groove sheets as flooring.

I'm tempted to give it a couple of hours tomorrow then if I haven't found it tell him to get someone else in. I mean, you shouldnt have earth leakage under normal conditions on a lighting circuit should you? Or do you get a bit from the sensors?

What are the acceptable lower limits for a 30mA RCD to trip?

Where do i stand not being registered? I mean I can swap a light fitting but can I replace an RCD or not?

 

[telectrix]

if it's a front end RCD it could be anything on the installation tripping it. also the RCD could be at fault.

 

[VoltzElectrical]

with the MCB for the circuit turned off, the RCD holds in. So he's got no outside or hall lights. And it doesn't trip out straight away either. Loose neutral sounds plausible but there shouldn't be any earth leakage accumulating in this circuit. I don't think its a trapped cable as all he's done is take down an old fitting and put up another one.

So, in summary, its not water in the fitting, and its definitely this circuit. Although, one switch is a two gang with this circuit and another circuit (kitchen/ utility room two way). I have advised him that this needs a sticker to warn anyone of two circuits in one switch.

he said on the phone that it tripped when he switched the kitchen lights on, but they only share a back box with the other circuit, and once again, with the MCB off for the outside lights etc.. the RCD holds in.

Can of worms springs to mind

 

[chronyx]

I had an intermittent outside light RCD trip that turned out to be a cross-connected neutral and earth.

 

[Marvo]

Ask the home owner where he wired his Christmas lights into. You'll probably find the redundant cable is still live and laying by the chimney where the 12 foot inflatable LED lit Santa used to stand.

 

[Edd]

IR the whole RCD protected side, you could be guessing its a fault with the outside lighting when theres somthing completly seprate causing it.
coincidence is the evil thing that screws up all our fault finding....

 

[VoltzElectrical]

surely IR testing the whole side isn't going to narrow anything down?

 

[VoltzElectrical]

here is a picture of the setup. I tested the lighting circuit allegedly causing the tripping problem (when isolated the RCD holds in) and All IR tests were greater than 299MOhms.

I then tried to ramp test the RCD but it tripped too quickly. I tried a standard auto test but again it tripped before x1.

I have suggested that we lose the upfront RCD and replace the main switch in each board.

Does anyone agree that this would provide a solution? Is the work notifiable? And what RCD main switch can I get for these boards?

Thanks again.

 

[GT1]

The RCD tripping before x1 sounds suspect.
Is there another one in the other box you can temporarily swop over and see if the fault moves with the RCD ?

 

[GT1]

I don't think it's notifiable yet. Your only fault finding as opposed to doing any install work.

 

[tony mc]

I take it that you want to remove the main RCD on the tails and replace both main switches on the CU for 30mA RCD's?

When you tested the RCD did you test with loads still on as it could easily be leakage on another or more than one cct!!

 

[VoltzElectrical]

replaced RCD today, with new enclosure. Same thing happens. So I start with everything off then switch on 1 at a time and retest. Eventually it trips on auto test with 1 and a half boards switched on.
Both boards will give a result individually, but anything more than a few circuits on the other one just won't hold an extra 15mA test current. The RCD is holding in with both boards on, so will wait and see if i get a call, when I will change the main switches for RCD's and ditch the up front.

 

[barnzi]

What are the boards supplying? If there's lots of switch mode power supplies (like in computers) or other mains filters connected to the circuits then the cumulative leakage current will trip the RCD. Splitting the whole smash into smaller RCD zones, i.e. with RCBOs might be the only way to overcome the leakage problem.