RCD tripping under load

[Liam_Spa]

Installing a split RCD board in a new barn conversion build, IR tests come out clear, ring continuity tests fine, but the RCD will trip out when something is plugged into the circuit, happens on both sockets that are currently running off that side of the RCD but when I swapped one over to the other RCD it didn't trip and I was able to obtain a ZS. Lighting circuits on that RCD is running fine, so have no idea what is causing both circuits to trip, never came across anything like this before as an newly qualified so first major job I've actually done!

 

[Darkwood]

Welcome to the forum Liam

 

[davesparks]

There is a fault on that socket circuit, sit down and think about what could cause such symptoms them carry out tests to find it.

You do find a lot of challenging situations when you are newly qualified, I found the best help was to give the guy I served my apprenticeship with a quick call to talk it through. For that matter I still do call him occasionally to talk over such problems.

 

[Pete999]

What exactly are you plugging in Liam? could be one of the appliances have a fault.

 

[Deleted member 9648]

Sounds like either a N-E fault, or you've mixed up your neutrals in the board. How did you test IR, and what were the results?

Always keep in mind with this sort of thing that there are no mysteries on normal installations. If the IR tests and other tests ARE fine, and the circuits are correctly connected at the CU ,and the RCD isn't faulty...it WONT trip. If it does you've missed something.

 

[Liam_Spa]

Sounds like either a N-E fault, or you've mixed up your neutrals in the board. How did you test IR, and what were the results?

Always keep in mind with this sort of thing that there are no mysteries on normal installations. If the IR tests and other tests ARE fine, and the circuits are correctly connected at the CU ,and the RCD isn't faulty...it WONT trip. If it does you've missed something.

Megger tester 500v DC between all combinations, greater than 1000mohms results. Checked neutrals in the board not crossed, in the right terminals. Trips when loop tester is plugged and testing zs.

 

[Dave OCD]

Yes it sounds like the neutrals need checking carefully to make sure they're on the right bar.

 

[Octopus]

When you did the IR circuits were all the CPC's connected to the earth bar in the CU and the MET?

 

[richy3333]

Megger tester 500v DC between all combinations, greater than 1000mohms results. Checked neutrals in the board not crossed, in the right terminals. Trips when loop tester is plugged and testing zs.

Megger MFTs don't go up to 1000Mohms? Is that what you are using?

How are you loop testing? 2 lead high will trip the RCD?

 

[HandySparks]

Megger MFTs don't go up to 1000Mohms? Is that what you are using?

Might not have been an MFT, might be a 'proper' Megger.

However, I was going to suggest that the OP needs to get his terminology right 'mohms' and 'zs'.

 

[Liam_Spa]

Megger MFTs don't go up to 1000Mohms? Is that what you are using?

How are you loop testing? 2 lead high will trip the RCD?

No trip setting on the loop tester....

 

[HappyHippyDad]

Installing a split RCD board in a new barn conversion build, IR tests come out clear, ring continuity tests fine, but the RCD will trip out when something is plugged into the circuit, happens on both sockets that are currently running off that side of the RCD but when I swapped one over to the other RCD it didn't trip and I was able to obtain a ZS. Lighting circuits on that RCD is running fine, so have no idea what is causing both circuits to trip, never came across anything like this before as an newly qualified so first major job I've actually done!

I have had a similar fault to this recently Liam (tripping RCD under load... at times!). When you are doing your IR tests this is a dead test so if an appliance is faulty it may not show this. My IR tests did actually come back as 0.2MΩ N-E but this is not enough to trip an RCD and this turned out to be an unrelated problem. I then clamped the tails with an earth leakage clamp meter and it read 28mA, which is why the RCD was tripping. I was a little lucky as the home owner had the washing machine on at the time which was the culprit, if they hadn't it may have taken a lot longer!

I would clamp the tails with an earth leakage meter (or clamp the main earth) and if that shows quite a few mA then start narrowing down the search by clamping each circuit and then each appliance(clamping each with your homemade lead if necessary). If it doesn't show an inbalance then switch on as much as you can around the house to try and see which appliance bumps up the mA inbalance.

ps... But if it is as Geoff has said below ( and trips straight away when anything is plugged in) then ignore everything above as it wont be that but it's useful to know!

 

[GEOFF S]

Hi

If its tripping as soon as something is plugged in, Neutral fault.

Cheers

 

[Basicspark]

I had a similar problem that was something very basic, when screwing back a socket outlet, the screw had slightly pinched a neutral. Try dropping sockets forward and see if it trips after this.

 

[Deleted member 9648]

I had a similar problem that was something very basic, when screwing back a socket outlet, the screw had slightly pinched a neutral. Try dropping sockets forward and see if it trips after this.

Didn't an IR test pick that up?

 

[marc8]

Hi Liam

A few years ago called out to a house RCD tripping randomly, reset everything fine for maybe a 10 seconds or even longer then same again.
went through tests stripped down whole board as this was a house on RCD main switch 30ma.
carefully tested got multitude of faults coming up through so much stuff plugged in I thought I had unplugged mainly NEON's on extension leads used all over.
so no faults on circuits as I went through & no reason for the RCD tripping tested RCD without circuits on fine & with circuits on fine.
anyway so random used a good load as I like to call it the Vacuum Cleaner in various circuits worked fine no tripping then few seconds later trip.
Earth leakage meter found that the whole house was pushing up over 25ma.
would definitely check my readings by testing IR & RCD, Then earth leak out with clamp see whats going on.

good luck

 

[Lucien Nunes]

I would clamp the tails with an earth leakage meter (or clamp the main earth)

These are not equivalent! If any leakage is taking place to something other than the CPC, or there is even just one parallel path from the MET such as the CPC connected to the heating system, then clamping the main earthing conductor will give a false reading, maybe very false. Do what the RCD does, and clamp L & N together to measure the difference between them.

 

[telectrix]

Didn't an IR test pick that up?

had same but with a L conductor. IR test showed >599Meg. but MCB tripped a few seconds after power applied.