mains circuit and rcd tripping

[scousespark]

Hi Bigmack.
He could IR test your circuits at the board, but thefault you described sounds like a fault in the circuits supplied by breaker 5. When RCDs fail it tends to be complete, not intermittent. I've not come across a faulty RCD tripping a breaker. If any other sparks have come across this scenario, I'd like to know what caused it.

When you say he tested at the board, did he do any work around your house?

 

[JohnD]

I'm wondering what he did, and what he found.

IR test and continuity/resistance at the CU would identfy a cable that had been damaged, e.g. with a nail through it.

So I wonder what the cause was then?

Multiple circuits through one MCB causing an overload trip, maybe, but I wonder what they were (householder in bed, so no shower or cooker in use). Maybe a washing machine and tumble dryer and dishwasher and imersion heater?

Maybe there was damage inside the CU?

I have a feeling the OP will come to regret not establishing the charging structure in advance

 

[scousespark]

I was thinking the same John. I know how much I charge (£25 per hour) and can multiply that by hours worked. Then add on parts and there's the price. I would also only work after the customer has agreed this up front.

I don't know how a faulty RCD can trip a breaker, but am always willing to learn new things.

 

[scousespark]

Multiple circuits through one MCB causing an overload trip, maybe, but I wonder what they were (householder in bed, so no shower or cooker in use). Maybe a washing machine and tumble dryer and dishwasher and imersion heater?
(

This wouldn't explain the RCD tripping, unless there are mutiple faults.

 

[JohnD]

indeed. Might there have been some kind of surge when (whatever it was that tripped the MCB) happened? Especially if there was a charred cable or arcing through the smoke.

I was certainly thinking cable damage the likely cause.

 

[BigMacUK]

The only comments I can give you are:

I had no appliances doing things for me in the background at either time. i.e. the kitchen kit were all idle waiting to be given work to do. Neither was sky+ springing to life with timed recordings or any such activity with other kit in the house.

The sparky turned up ( very late ), and asked me what had happened so I described the two circumstance. Stated there was no timed activity that would come alive from such as central heating or so and again highlighted I was in bed with various appliances off on second time.

He produced tools and steps, turned power off and poked around the consumer unit then from wall socket tested the rcd several times. This took about 10-15 mins, and he decided the RCD needed replacement. Didn't have one in the van - scooted to shops for maybe half hour, came back fitted. All in, from first arrival to last departure was on the job a wee bit over an hour or so.

I'm interested in if indeed it has been a fix or if work has been done that didn't need it. Along with what the invoice, wondering what it will charge when it arrives. As the sparky couldn't tell me, I phoned the company and they couldn't tell me either and was told to wait for invoice.

A little more detail on the delays. Sparky was due for 9am. I called them a few mins after 10am to be told "sorry", and a story of them being in chaos and the sparky would be with me by 11am. He didn't arrive till approx 11:35am, and was out the door circa 12:45pm if that.

 

[securespark]

How did he decide the RCD was faulty?

Did he test it in isolation? IE with all circuits disconnected from it?

If he did not, then it is highly likely that something in circuit could have affected the readings he got.

Today, I went to an RCD-tripping fault. I did an EFL soft test. It tripped the RCD. I switched off all circuits. The soft test ran through OK. Then I reconnected, one by one, the MCB's until the RCD tripped again. That was the faulty circuit. On it was a damp external socket.

So, you see, testing the RCD from a socket outlet can give highly misleading results.

The first guy to test the RCD I looked at today told me it was faulty & needed exchanging. But it was a fault on a circuit attached to that RCD that was causing the tripping, not the unit itself.

 

[BigMacUK]

I dont wish to give misleading or confusing information that may be out of time period from observing the work.

I know at some point early on during the tests, all the red cables that fed top down into each of the MCB were pulled out and he was testing those one by one.

The RCD test was done by him plugging a testing tool into a wall socket in the kitchen, tripping the RCD from there - reset the RCD, rinse and repeat this several times over.

I'm fairly sure this was after the test on each of the red wires, but can't for life of me recall when they were re-wired back into MCB. Could such a test work if the red cables were out at the time?

 

[scousespark]

Sounds a bit strange mate.

It takes more than a few minutes to test the fault you had. If he left everything switched on he was bound to get a problem with the RCD.
When he disconnected the red cables, did he also disconnect the black cables too?

Also, if he didn't do any work away from the board, what circuits was he splitting?

 

[BigMacUK]

sorry scousespark I don't know about the blacks. The reds are what stuck in my mind the most. I just remember studying those wondering why one MCB had one going into it, other had 4 and so on. To be honest, I dont actually recall seeing black. Guess I fail an observation test!

Seriously all the work he did do was at the consumer unit, other than plug in the test harness to wall socket at kitchen whilst doing the RCD test. Only other bits done, was to turn off the power at the meter box outside the house when he came back with the new parts.

I know when he went out shopping, everything was wired up again. It may be possible, he pulled the wires tested them one by one all out, put them back in and tested the RCD. I just can't be sure on that sequence of events.

 

[BigMacUK]

Oops missed the splitting circuit question.

If you're asking about what went on with MCB 5, it apparently had the downstairs and upstairs wall socket circuits in there together. I didn't realise this at the time. He bought a new MCB to go into a spare slot and allocated the dowstairs to it and left the upstairs in 5.

Is that what you meant or have I misunderstood?

 

[scousespark]

That makes sense. The 4 reds would have been the 2 rings.
I hope your fault has been cleared and the price is right for you.

 

[BigMacUK]

You're not alone with those hopes!

I think, I've a natural distrust for things I don't understand and get rather anxious and frustrated about them. Couple this with the cowboys highlighted TV it doesn't really help.

After folks posted here, I was half expecting a cable fault to be found and now that it's been "fixed" with replacement RCD and splitting 1 MCB allocations over 2 MCB - the "easy" fix, I'm just loaded with self doubt! Especially when consider the brief time of 15-20 minutes it took to find the fault, and folks also post here they think this was quick. Along with the idea, it's not like the problem was reproducible like overloading a circuit with appliances. So haven't got a test scenario that proves the problem, make "fix", and re-test to find the failure point removed. Only time will tell, if don't find any unexpected trips - but, as was previously written this could be a "magic self fix" where wires have burned away, that is actually still dangerous.

Granted though, the guys on forum haven't seen the fault or experienced it for themselves and getting informations only from what I can describe / remember. The sparky that came out, did a job based on what he could see and do, and at least gave the impression of being competent!

 

[pbar]

You're not alone with those hopes!

I think, I've a natural distrust for things I don't understand and get rather anxious and frustrated about them. Couple this with the cowboys highlighted TV it doesn't really help.

After folks posted here, I was half expecting a cable fault to be found and now that it's been "fixed" with replacement RCD and splitting 1 MCB allocations over 2 MCB - the "easy" fix, I'm just loaded with self doubt! Especially when consider the brief time of 15-20 minutes it took to find the fault, and folks also post here they think this was quick. Along with the idea, it's not like the problem was reproducible like overloading a circuit with appliances. So haven't got a test scenario that proves the problem, make "fix", and re-test to find the failure point removed. Only time will tell, if don't find any unexpected trips - but, as was previously written this could be a "magic self fix" where wires have burned away, that is actually still dangerous.

Granted though, the guys on forum haven't seen the fault or experienced it for themselves and getting informations only from what I can describe / remember. The sparky that came out, did a job based on what he could see and do, and at least gave the impression of being competent!

I wouldn't be too worried if I was you. Your electrician (who you have no reason to doubt and it's always good when you have faith in their competence) ran tests, decided the RCD was faulty, changed it and all's been well since. Your sockets have been split over two MCB's also which is better and more the norm. Chances are if it was a dodgy cable somewhere then it would still be tripping, it's unlikely to have magically fixed itself at the same moment that the RCD was changed. I would be inclined to think the electrician has fixed it, and hopefully you won't have any more trips. I too hope the price is good for you.

 

[Softus]

If a dangerous cable fault existed, and still exists, and wasn't detected, and wasn't addressed, then the danger still exists.

Personally, as a potential punter, I wouldn't be satisfied without an explanation of the MCB tripping, which is precisely one of the two things that was paid for, and the single thing that is still missing.