New consumer unit - diagnostics challenge
- Thread starter SimonH2
- Start date
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Based on Alarm saying that PE means Line + CPC reversed my guess would be L + N mixed up in the input to the breaker in some way, though I don't see quite how you could manage that given presumably the neutral will be a fly lead coming off and the live taken from the bus bar that will be spaced appropriately, plus that doesn't quite fit the message on the tester?
It's true that there can't be that sort of issue with RCBOs. However, when I raised the neutral bar issue, I was thinking of a situation in which the errant RCBOs were connected to a 'neutral' bar different from the one the other RCBOs were connected to AND that first 'neutral' bar was not actually connected satisfactory to neutral.
As you say, Simon is not being totally clear. As I said, if he meant that both L&N of the load had been disconnected from the RCBO, then I can see nothing other than a faulty RCBO that could render it 'unsettable'.
If only the line conductor of the load were disconnected then, in a TT installation, a N-E fault can theoretically make an RCBO operate even if none of the circuits are on load (due to a current flowing 'backwards' through the N side of the RCBO from an 'above earth potential' neutral supply to the 'true earth' of the TT electrode) - but that ought to affect all RCBOs connected to the same neutral (bar).
As you say, I'm not even sure, from what Simon is syaing, what is being tested when the tester 'beeps and displays PE' with circuits 7 & 8. We're also not told whether, assuming the circuits have been energised, circuits 7 & 8 'work' or not. Some more clarity/detail would certainly be helpful.
Kind Regards, John
Ah, I see what you are getting at.
But the problem isn't about the breakers tripping, see below.
Go back and read the original description.I'm not following what you are testing for here?? Is it me? What test are you performing?
The only reason that I can think of that an RCBO would trip without a load (line conductor) connected to it would be a neutral/earth fault on that circuit - but the other circuits would have to be under load.
You're not being very clear, I'm afraid.
Cct 6 wouldn't set. That was a faulty breaker. After changing it, ccts 1-6 all operate and test OK.
Ccts 7&8 set, but the test set throws up an error, and there's no indication on a voltage indicator put across the output terminals on either breaker.
So you've got an RCBO connected to the live bar, it's blue wire is connected to it's place in a neutral bar, there is no connected load wiring (neutral or line), the breaker has set, but you get no supply from it's load terminals. And it's not just one RCBO, there's two of them doing the same thing.
If you are following, by now you are probably thinking, as I did, that there's a fault in the breakers.
I put one side of the indicator on the main neutral terminal, got a light from the live bar terminal on the breaker, touching the live load terminal made the breaker trip (my indicator takes enough current to do that).
When I tried probing between live bar and the breaker neutral load terminal, I got ... nothing.
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This isn't as simple as not having a good neutral connection to the breaker (either at the breaker or in the neutral bar), coupled with a confusing error message from the tester as it might be picking up some sort of induced current in the neutral load terminal is it?
This is, indeed, getting very frustrating! If you're seeing voltage between the RCBOs' L output and 'the main neutral terminal', but not between the RCBOs L & N outputs then either the RCBO is faulty (no continuity between N input and N output when set) OR the neutral (bar) to which the RCBO is connected is not actually at neutral potential. I can see no other possibilities.
Kind Regards, John.
Well two of you have spotted the fault now. Difficult giving enough information but without giving the game away too easily Interesting that in spite of several times asking "what would you test/do next ?", there were very few suggestions on that front.
One of the neutral bars wasn't in fact connected to the main neutral terminal on the incomer switch
This family of boards comes in different configurations, the non-split option still has a split neutral bar, and a solid copper link goes between them. The arrangement is that there's a solid bar between incomer and first neutral bar in top left of board, then a link from the other end of that bar to the second bar to it's right. They occupy most of the left half in the top of the board, and the single earth bar occupies the right hand top area.
Yes the link was fitted, yes the screws were tight ... but onto the insulation which was a smidgen too long.
That's why 6 breakers worked just fine - they were connected to the first neutral bar.
The next 2 were connected to the non-connected neutral bar and so had no neutral. Thus they either had a floating neutral, or a neutral pulled live by a connected load (initially, before we disconnected all the load wiring). The error from the tester was indeed misleading, the sparky believed it to mean a phase-earth error which had us looking at things other than a neutral fault for a while.
Not only that, but we also had the separate and unconnected breaker fault - so we couldn't be sure if there was one fault or two, or a batch of faulty breakers and all three were duff
Of course, the worrying aspect of this is that in this case there was a definite fault and it was picked up during testing. Had the screw "just" made it through the insulation, or the link had enough twist to touch elsewhere, then there could have been enough contact to pass testing, but not enough to carry large currents long term - with the obvious potential for a fire at a later date. Not likely in this case with only two lighting circuits running through the link, but worrying all the same and it'll be reported to the supplier as a product safety issue rather than just a faulty item.
Interesting that in spite of several times asking "what would you test/do next ?", there were very few suggestions on that front.One of the neutral bars wasn't in fact connected to the main neutral terminal on the incomer switch
This family of boards comes in different configurations, the non-split option still has a split neutral bar, and a solid copper link goes between them. The arrangement is that there's a solid bar between incomer and first neutral bar in top left of board, then a link from the other end of that bar to the second bar to it's right. They occupy most of the left half in the top of the board, and the single earth bar occupies the right hand top area.
Yes the link was fitted, yes the screws were tight ... but onto the insulation which was a smidgen too long.
That's why 6 breakers worked just fine - they were connected to the first neutral bar.
The next 2 were connected to the non-connected neutral bar and so had no neutral. Thus they either had a floating neutral, or a neutral pulled live by a connected load (initially, before we disconnected all the load wiring). The error from the tester was indeed misleading, the sparky believed it to mean a phase-earth error which had us looking at things other than a neutral fault for a while.
Not only that, but we also had the separate and unconnected breaker fault - so we couldn't be sure if there was one fault or two, or a batch of faulty breakers and all three were duff
Of course, the worrying aspect of this is that in this case there was a definite fault and it was picked up during testing. Had the screw "just" made it through the insulation, or the link had enough twist to touch elsewhere, then there could have been enough contact to pass testing, but not enough to carry large currents long term - with the obvious potential for a fire at a later date. Not likely in this case with only two lighting circuits running through the link, but worrying all the same and it'll be reported to the supplier as a product safety issue rather than just a faulty item.
A
Alarm
How many actually inform the manufacturers of "little" faults?
I do with the equipment I use. Even had entire sections of manuals re-written.
In that case, I reckon I'll give myself a little creditWell two of you have spotted the fault now. Difficult giving enough information but without giving the game away too easily
, since my first contribution to this thread was:True, I didn't explicitly answer that - but I think it's implicit in what I said in that first contribution that the first thing I would have done would have been to investigate what, if anything, the 6/7/8 neutral bar was actually connected to!
Kind Regards, John.
True. But then it would have spoiled it for the rest to give the game away too soon.In that case, I reckon I'll give myself a little credit
Actually, 6 is connected to the same bar as 1-5 - the fault on cct 6 was a bit of a curveball and merely a coincidental fault.
I guess the main lesson I learned (or rather, was reminded of) is don't take the simple things for granted. The link between the neutral bars was there, the screws were tight, what could possible go wrong with a bit of copper bar and two screws
It was an awkward little *** to get back in as well. A small "staple", to be fitted into two holes, with all the wiring now in the way.
Yes. I suspected that my initial suggestion was probably more-or-less right from the fact that your response to my comment was conspicuous by its absence, whereas you responded to most other people! I guess it all goes to show that non-electricians have been known to have their uses
Indeed, it's partially a consequence of the teaching/practice that there should be no visible copper. I have to say that (despite the flak it may cause), I have always try to adopt the opposite practice - i.e. to be sure that there is always a tiny bit of bare copper visible, to reassure me that I have indeed tightened onto copper, rather than insulation.I guess the main lesson I learned (or rather, was reminded of) is don't take the simple things for granted. The link between the neutral bars was there, the screws were tight, what could possible go wrong with a bit of copper bar and two screws
Mind you, like (I imagine) most of us, I have been 'caught' by this problem. I think G/Y sleeving is perhaps the biggest bugbear. Unless it's very tight on the conductor (and there are not enough sizes of sleeving around for it to always to be tight) it's only too easy to push the sleeving into a terminal whilst holding the wire in place to tighten the screw ... and that's a good illustration of why post-work testing is important, since a non-connected CPC will not otherwise be noticed.
Thanks for the interesting diagnostic challenge - and glad you got it sorted!
Kind Regards, John.
That was the crucial piece of information that dribbled out eventually - I was initially labouring under the misaprehension that it was a single neutral bar CU.
Does JohnW win 50p for being the first pretty much spot on?
No money needed - the 'honour' is adequate - but I suppose you could touch bthe 'Thanks' button if you wanted to
Kind Regards, John.
No money needed - the 'honour' is adequate - but I suppose you could touch bthe 'Thanks' button if you wanted to
Kind Regards, John.
Help yourself to a biscuit John!
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