UK RCBO intermittent tripping advise??

[leebut]

Hi Guys


Just installed a RCBO board to replace an old Wylex consumer unit that had Bs60898 MCB's fitted and an RCD main switch customer supposedly hadn't had problems in the past (not quite sure thats now true) when I carried out the EICR I found a problem on the outside garden lights, so until the summer I've disconnected the garden lights circuit so all should be good.

The house is 25 years old and has minimal work carried out on it so no DIY Dave stuff, I finished fitting the board yesterday and went back today to install some outside wall lights but had issues all day with the kitchen lights tripping the RCBO every so often when the light switch is operated (but not every time) the kitchen, utility and lounge are all on the same circuit, only the kitchen lights trips the RCBO, question is has anyone had issues in the past with Low voltage downlighter's supplied by one large transformer tripping the RCBO I disconnected the transformer prior to the IR testing which came back almost perfect with the switches operated both ways etc.

Refitted the transformer and its tripping spent ages on this today, I've advised customer I think the Transformer is on its way out and recommended I install new downlight with GU10 LED lamps to replace the MR16 Halogens, everything was fine with that idea until husband came home and doesn't want to spend any more money without knowing this is going to cure the issue.

Anyone had anything similar??

 

[radiohead]

I would say a 6A D type MCB or RCBO would have a 50% (approx) chance of being non compliant in a domestic situation as the Zs would have to be max 1.46Ω (TT).
I would say a 32A D type MCB or RCBO would have a 98% (approx) chance of being non compliant in a domestic situation as max Zs is 0.28Ω (TT).

My aspergery brain starts overheating when the word 'likely' is used as it is so subjective! It doesn't mean anything in this scenario. Even my approximations above are ridiculous as they are only ever so slightly less subjective.
It's a bit like that old 80's film 'war games' when the computer tries to find a winner in nuclear war and breaks down due to infinite 'no win' outcomes.

I will now stop drinking coffee.

I assume you mean TN....not TT? Any rating of type D would have a 100% chance of being compliant in a correctly designed TT.
I agree on a TN in many existing situations a device exceeding 6a may be non compliant, but in new additions, alterations and new installations in domestics any rating of a type D mcb is probably 100% likely to comply because virtually all circuits will have RCD protection, and an RCD is a permitted means of earth fault protection. RCD's are not only for additional protection, something that is often overlooked.

 

[Dave OCD]

And now you're saying pretty much what I was getting at, bottom line is that a type D is not a good design choice for a new domestic install.

 

[radiohead]

And now you're saying pretty much what I was getting at, bottom line is that a type D is not a good design choice for a new domestic install.

But that doesn't make it non compliant. Sorry but I get irritated by this, I've even heard talk in the wholesalers that only type B is permitted in domestics. That's how these phantom regs come about

 

[Midwest]

When I did CU changes, they we’re mostly simple ones, never did an EICR before, but soo learnt to do some testing after my quote was approved and before taking the old one off the wall.

However in this instance I’m not sure if an EICR would of discovered the fault? Albeit, the reasoning behind the change, would of been cause for concern.

Hope OP has something in his T&C’s about remedial work, with CU changes.

 

[Andy-1960]

Why not swap the kitchen transformer with one of the other identical units and see if the fault moves.

 

[leebut]

Why not swap the kitchen transformer with one of the other identical units and see if the fault moves.

Each transformer has eight sets of T&E going to it can’t be arsed if I’m honest now!!

 

[leebut]

Well after ordering a C Type RCBO from my local stockist, i thought id temporarily swap the B Type with an MCB so it wouldn't keep tripping now the husband has completely denied any conversation with his wife over the extra cost of replacing the downlight with GU10's, he's more than happy for me to replace them tomorrow I wonder if over the weekend he's had his ear bent so many times about the cost he wants to keep her in doors quiet!!!!