Dual RCD Problem

[Pauldicker]

Dear all

I have been called out to a customer today as they have been experiencing tripping issues. However sometimes its one rcd then a while later it may be the other and sometimes its both at the same time.

I have looked at appliances, e.t.c however they do not cross both circuits. The customer said its happened over the last few months. They have experienced regular power cuts so i did wonder if a power surge could be the issue.


Any ideas?

 

[Pete999]

Any recent work/alterations done??

 

[Pauldicker]

Any recent work/alterations done??

No nothing

 

[bigmark]

what make are they

 

[joehat]

Shared neutral on stair lights?


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[Octopus]

I would start investigations using my earth clamp meter and then test the rcds.......

 

[Pauldicker]

But what would explain them tripping individally or both together. This is also when under no load

 

[Octopus]

But what would explain them tripping individally or both together. This is also when under no load

Err..... A fault or faults.

Just this week I traced a "no load" fault to cables behind a socket where the earth was touching the live

Does it happen more frequently during wet weather?

 

[snowhead]

But what would explain them tripping individually or both together. This is also when under no load

RCDs trip either because they are faulty or because they are detecting an imbalance.
They may not have any apparent load on them but may have a fault current through them.

Trying to guess why at this stage is impossible, work that out afterwards.

It wouldn't be out of the question after the fault is found, possibly to be an alteration or meddling, for the customer to admit to such.

 

[Pauldicker]

They noticed it more this tuesday with the rain. However there were a few power cuts in the road. I could not find any obvious water ingress

 

[Pete999]

Any extrnal electrics, you mentioned it tripped after a rainy day?

 

[Deleted member 9648]

Have you done any IR tests? That's the first thing I'd do. Leave everything plugged in and test LN-E. NOT L-N!
I can recall only a handful of RCD tripping issues I haven't quickly traced by IR testing.

 

[Pauldicker]

I havent done an ir test yet i wanted to narrow it down before i start charging. Its been happening on and off for a couple of months. But as i described it could be either of the rcd's or both at the same time.

 

[David M]

A few years back I went out to a property that had a "nuisance" tripping problem. It turned out to be a "faulty" extension lead. In fact it was a four gang short extension that the owner of the property later admitted he had changed the plug on a while back. He had mistakenly connected the earth and neutral wires the wrong way round. All that was ever plugged in was his alarm clock and the RCD only tripped occasionally.

My point being that part of your investigation into finding the fault may include quizzing the property owners. They may not realize the significance of something so simple, much like my example above.

 

[sparksburnout]

I havent done an ir test yet i wanted to narrow it down before i start charging. Its been happening on and off for a couple of months. But as i described it could be either of the rcd's or both at the same time.

I am a bit puzzled by this, what are you charging?? MFT batteries? Customer? Braincells?? in like a bull?

 

[davesparks]

I havent done an ir test yet i wanted to narrow it down before i start charging. Its been happening on and off for a couple of months. But as i described it could be either of the rcd's or both at the same time.

For goodness sake man, you are supposed to be a professional electrician are you not? Charge an appropriate callout for the first hour you are there and an hourly rate after that. Having a look, narrowing down, asking a forum, etc etc is hardly the work of a professional is it? I dread to think what your customer must think of you!

Why would you not carry out an IR test when you have the clear symptoms of a very common fault, namely a N-E fault.,

 

[Pauldicker]

Thanks for the advice guys i think this one is going to be a thorough investigation of every circuit to find the cause.

 

[HappyHippyDad]

As above Paul I would definitely be doing an IR test between N-E to start off with. Asking questions as you are doing would be more suited to asking the client as they will be able to perhaps give you some clues (i.e time of day, heavy rain, when an appliance is switched on etc) whereas we would just be guessing. It's a bit like saying to a mechanic 'my cars broken down could you tell me whats wrong please'. The thread below is just one of many on the forum that talks about fault finding tripping RCD's.

http://www.electriciansforums.co.uk...ical-forum/64088-rcd-tripping.html#post640772

Here is a PDF about tripping RCD's that is quite interesting as well.

View attachment understanding RCD's and tripping problems..pdf

In addition 'I think' Richard Burns has talked in a post (and drawn some good diagrams) about the 'opposite' RCD tripping. I.e a circuit on the right of the board making the RCD on the left trip. I can't quite get my head around this as there shouldn't be an imbalance. Anyway, that's digressing and I think you should start at the beginning with your N-E tests!

 

[Octopus]

As above Paul I would definitely be doing an IR test between N-E to start off with. Asking questions as you are doing would be more suited to asking the client as they will be able to perhaps give you some clues (i.e time of day, heavy rain, when an appliance is switched on etc) whereas we would just be guessing. It's a bit like saying to a mechanic 'my cars broken down could you tell me whats wrong please'. The thread below is just one of many on the forum that talks about fault finding tripping RCD's.

http://www.electriciansforums.co.uk...ical-forum/64088-rcd-tripping.html#post640772

Here is a PDF about tripping RCD's that is quite interesting as well.

View attachment 32176

In addition 'I think' Richard Burns has talked in a post (and drawn some good diagrams) about the 'opposite' RCD tripping. I.e a circuit on the right of the board making the RCD on the left trip. I can't quite get my head around this as there shouldn't be an imbalance. Anyway, that's digressing and I think you should start at the beginning with your N-E tests!

Why just the N-E tests? When doing IR tests you need to do them all and in a logical manner

 

[HappyHippyDad]

Why just the N-E tests? When doing IR tests you need to do them all and in a logical manner

That's what I tend to start with Murdoch, that usually shows up the faulty circuit, but then if still no luck then the earth clamp meter comes out.

 

[Richard Burns]

In addition 'I think' Richard Burns has talked in a post (and drawn some good diagrams) about the 'opposite' RCD tripping. I.e a circuit on the right of the board making the RCD on the left trip. I can't quite get my head around this as there shouldn't be an imbalance. Anyway, that's digressing and I think you should start at the beginning with your N-E tests!

I hope I have not provided unclear information.
One key thing to remember is that (barring irregular voltage transients) if an RCD or RCBO trips then the fault must be on the circuit(s) that the RCD is protecting, the fault cannot be on a circuit not connected to the RCD.

However for a neutral earth fault present on a circuit protected by the RCD, a load on a circuit not protected by the RCD can allow diverted current to flow through the NE fault on the faulty circuit and trip that RCD, however the fault is on the circuit protected by the RCD, not on the circuit that appeared to cause the RCD trip.

 

[Adam W]

When you say "dual RCD" do you mean 2 RCDs inline?