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??

 

[leebut]

Yes he can afford to make his home safer, and having the CU replaced is doing exactly that.
However he shouldn't have to pay for the replacement of installed equipment just because the person who installed the CU has fitted the wrong protective device for that equipment.

why is it my installation problem after fitting a Type B RCBO theres a eight more of these trannys fitted to other circuits on all the upstairs lights in the house these are all working fine all installed on B10 RCBO's just this one part of the circuit, it doesn't trip every time you turn the light on it might be every twenty to thirty operations of the switch that causes the breaker to trip
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It’s called upselling.
Halogens are old hat. Suggest to change them for the reasons of energy saving

his wife is fine with the idea partly because all the existing fittings are brass and she would prefer chrome and likes the idea of less power consumption

 

[davesparks]

why is it my installation problem after fitting a Type B RCBO theres a eight more of these trannys fitted to other circuits on all the upstairs lights in the house these are all working fine all installed on B10 RCBO's just this one part of the circuit, it doesn't trip every time you turn the light on it might be every twenty to thirty operations of the switch that causes the breaker to trip

Because you have fitted an RCBO which appears to be tripping on the normal inrush for the transformer. You took a circuit which was protected by a type D device and replaced it with a type B, it was your decision to change the tripping curve of the protection and now it is tripping as a result of your decision.
If its not tripping every time then that suggests it is on the borderline of being OK for that RCBO but occasionally the switch is operated at exactly the right (or wrong) moment to cause the inrush to be at its highest.
Are all of the transformers exactly identical with exactly the same lamps connected to them and exactly the same length of cable feeding them? No? Then there's your answer to why some trip and others don't, they arent all identical.

 

[leebut]

Because you have fitted an RCBO which appears to be tripping on the normal inrush for the transformer. You took a circuit which was protected by a type D device and replaced it with a type B, it was your decision to change the tripping curve of the protection and now it is tripping as a result of your decision.
If its not tripping every time then that suggests it is on the borderline of being OK for that RCBO but occasionally the switch is operated at exactly the right (or wrong) moment to cause the inrush to be at its highest.
Are all of the transformers exactly identical with exactly the same lamps connected to them and exactly the same length of cable feeding them? No? Then there's your answer to why some trip and others don't, they arent all identical.

The Transformers are all the exact same model and size and all have six halogens MR16 connected to them only difference I can see is cable length, its very intermittent the tripping at least twenty flicks of the switch before it trips, the consumer unit has 8 lighting circuits four of which are Type D 10 amp (two are protecting the exterior flood lights), two have Type B 10 amps and two Have Type B 6 amp like I say the rest of the house are fine just this one Tranny

 

[davesparks]

The Transformers are all the exact same model and size and all have six halogens MR16 connected to them only difference I can see is cable length, its very intermittent the tripping at least twenty flicks of the switch before it trips, the consumer unit has 8 lighting circuits four of which are Type D 10 amp (two are protecting the exterior flood lights), two have Type B 10 amps and two Have Type B 6 amp like I say the rest of the house are fine just this one Tranny

If you are convinced it is this transformer then replace it, but don't be surprised when the customer says they aren't paying for it.

Presumably this worked fine before you replaced the CU?

 

[leebut]

If you are convinced it is this transformer then replace it, but don't be surprised when the customer says they aren't paying for it.

Presumably this worked fine before you replaced the CU?

I first went to this house in November and they had issues of tripping on the old Wylex RCD mainswitch but they put this down to an issue with the under tile heating in one of the bathrooms as the muppet installer disconnected the CPC due to tripping problems turns out he'd damaged the cable and they received a shock in the shower I disconnected the heat mat from the power supply and programmer.

Roll on to me going back to the house in February they still had a problem of nuisance tripping knocking the house off completely this was put down to the garden lighting as they're all knackered and possible water ingress in the adaptable boxes (all are 25+ years old) when I tested the circuits nothing was showing up on IR testing Zs all fine but odd trip here and there, other than the garden lighting issue.

they asked my advice on the existing board and the problems when it tripped I suggested the RCBO option on a new board which they both agreed on, and thats up to present day.

 

[ipf]

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He affords them by not paying out for unnecessary work to be done on his house.
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Nooo, but it helps a bit to pay the fuel bill.....

 

[leebut]

He affords them by not paying out for unnecessary work to be done on his house.
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Nooo, but it helps a bit to pay the fuel bill.....
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He's an accountant so probably doesn't pay the taxman very much money each year

 

[Markyd]

So the house had a few probs before you changed the board.....Alarm bells should have rung then.EICR was prob ok but you should have put in writing that any remedial work that needed to be done after board change would be down to them to cover cost of investigation and remedial work

 

[Wilko]

Hi - if I’ve understood correctly it’s just this one circuit with the one transformer that sometimes trips? - other than changing the RCBO as already suggested you could perhaps also :

- confirm from the board the circuit has “excellent“ continuity (with the transformer primary bypassed) and insulation resistance.

- see if the fault moves with the transformer.

-replace the switch, as it’s not impossible that contact bounce is annoying the RCBO somehow ...

 

[radiohead]

There's your answer then, a D type is most unusual and probably non compliant in a lot of domestic situations, I expect the new RCBO serving the kitchen lights will have a 'B' tripping curve, if the customer doesn't agree to new LED lights a C type 10a RCBO might do the trick.
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The D type MCBs were originally fitted to counteract the high inrush current and nuisance tripping with the old toroidal transformers I expect.

Why would a type D 'probably be non compliant in a lot of domestic situations'?
If the measured Zs is satisfactory.....and anyway the OP stated there was originally an RCD main switch which largely negates any OCPD Zs issues.

 

[Dave OCD]

Why would a type D 'probably be non compliant in a lot of domestic situations'?
If the measured Zs is satisfactory.....and anyway the OP stated there was originally an RCD main switch which largely negates any OCPD Zs issues.

I knew there would be at least one picking up on that, I was referring to existing installations where there may not be RCD protection on the lighting,and the measured Zs could be unsatisfactory.How often have you seen type D MCBs in domestic installations ?

 

[HappyHippyDad]

I think it’s fine to offer the option of replacing the ELV lights but I’d be making it clear that it is just a good idea and not a necessity. I would be changing the B type RCBO for a C type free of charge if they chose not to change to GU10’s.

 

[radiohead]

How often have you seen type D MCBs in domestic installations ?

Hardly ever, doesn't mean they are likely to be non compliant though.

 

[Vortigern]

Bit of a stab in the dark here. I have encountered tripping on RCD where there is two way switching due to the way the 3 core was connected. By changing the cores around at the switches the RCD tripping stopped due to the "centre" (for want of a better description) cable being adjacent to the cpc no longer. You did seem to mention testing the switches both ways. Sorry if I have misunderstood, but I took that as there is two way switching in the kitchen?

 

[HappyHippyDad]

Hardly ever, doesn't mean they are likely to be non compliant though.

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.