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??

 

[Dave OCD]

This could simply be high inrush current being drawn by the transformer causing the overcurrent part of the RCBO to operate.
Was the previous MCB that covered these lights a 'C' tripping curve or perhaps 10a rated by any chance ?

 

[littlespark]

Transformer with halogens? If the rcbo always trips when this circuit is turned on, then 100% the tranny.
Is it 25 year old same as house? I’d say it’s reached it’s expiry date.
For the cost of a few new LED downlights, the less heat generated and power consumption, it’s a no brainer

 

[leebut]

This could simply be high inrush current being drawn by the transformer causing the overcurrent part of the RCBO to operate.
Was the previous MCB that covered these lights a 'C' tripping curve or perhaps 10a rated by any chance ?

Hi Dave

majority of the lighting circuits in the CU were D10 Wylex (PSB 10D) MCB apart from two small circuits that had B6 (NSB06)

lee

 

[pc1966]

Changing to LED lamps makes a lot of sense in any case, lower power consumption and much longer life.

You might want to double-check the insulation to see it is not L-N fault either, but if nothing has changed since the inspection then the previous suggestion on the over-current tripping sounds plausible. Also double check the isolation of circuit neutrals, but a stupid "borrowed neutral" would likely see another RCBO trip occasionally instead.

Finally if you have a sensitive enough clamp ammeter (looks on desk, sees DiLOG DL6518 sitting there) you could check the residual current by putting L&N through it to see if there is anything leaky when running that gets anywhere close to 15mA.

 

[leebut]

Transformer with halogens? If the rcbo always trips when this circuit is turned on, then 100% the tranny.
Is it 25 year old same as house? I’d say it’s reached it’s expiry date.
For the cost of a few new LED downlights, the less heat generated and power consumption, it’s a no brainer

Hi mate


yeah the house has a few of these old drum type Trannys fitted this one has six outlets going to the downlight etc, I explained this to the customer she was happy for me to do work then texts me saying husband doesn't want to spend £200ish to rectify this nuisance tripping unless I can guarantee its the problem (he's just bought a brand new Porsche so probably skint)

 

[Dave OCD]

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.

 

[leebut]

Changing to LED lamps makes a lot of sense in any case, lower power consumption and much longer life.

You might want to double-check the insulation to see it is not L-N fault either, but if nothing has changed since the inspection then the previous suggestion on the over-current tripping sounds plausible. Also double check the isolation of circuit neutrals, but a stupid "borrowed neutral" would likely see another RCBO trip occasionally instead.

Finally if you have a sensitive enough clamp ammeter (looks on dsek, sees DiLOG DL6518 sitting there) you could check the residual current by putting L&N through it to see if there is anything leaky when running that gets anywhere close to 15mA.

I've got an earth leakage clamp meter didn't try it because I was convinced it was the Tranny anyway, I think its a no brainer to change fittings to GU10 and LED lamps

 

[pc1966]

The D type MCBs were originally fitted to counteract the high inrush current and nuisance tripping with the old toroidal transformers I expect.

Missed that, but that would appear to explain everything!

Should have seen it coming though, as in the past (not domestic wiring) we put in NTC thermistors on the toroid supply to cut the switch-on surge and increase the life of switching relays. They were burning out after a few k operations and not the 50k that was needed.

 

[leebut]

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.

Hi Dave


thanks for the info and advice, to me the D10 MCB (there are 4 of them two seeing the light circuits and two for the external flood lights around the house) looked to have been changed at some point from the original NSB breakers that makes up the rest of the board so your probably right about changing to a C type RCBO, I thought the PSB breakers were for non domestic board and three phase boards!!

 

[davesparks]

I've got an earth leakage clamp meter didn't try it because I was convinced it was the Tranny anyway, I think its a no brainer to change fittings to GU10 and LED lamps

It's a no brainer to expect you to correct your error at your own cost, the customer shouldn't have to pay any extra because you have fitted protective devices which are unsuitable for the installed equipment.
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Is it 25 year old same as house? I’d say it’s reached it’s expiry date.

Why is that? A toroidal transformer can be expected to last longer than that without issue.

 

[MJPD29]

Hi mate


yeah the house has a few of these old drum type Trannys fitted this one has six outlets going to the downlight etc, I explained this to the customer she was happy for me to do work then texts me saying husband doesn't want to spend £200ish to rectify this nuisance tripping unless I can guarantee its the problem (he's just bought a brand new Porsche so probably skint)

If he can afford the Porsche he can afford to spend a few quid making his home safer. I despise people like that. But if the circuit has tested ok and there are no faults then I agree with the advice to change it to a type C. Cant imagine earth leakage being 30ma.

 

[leebut]

If he can afford the Porsche he can afford to spend a few quid making his home safer. I despise people like that. But if the circuit has tested ok and there are no faults then I agree with the advice to change it to a type C. Cant imagine earth leakage being 30ma.

Not just the Porsche, theres a Mercedes, a Mini and BMW RV on the drive wonder how he affords all of them and don't want to spend a few quid on his house Typical accountant!!

 

[davesparks]

If he can afford the Porsche he can afford to spend a few quid making his home safer. I despise people like that.

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.
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Not just the Porsche, theres a Mercedes, a Mini and BMW RV on the drive wonder how he affords all of them and don't want to spend a few quid on his house Typical accountant!!

He affords them by not paying out for unnecessary work to be done on his house.

 

[littlespark]

It’s called upselling.
Halogens are old hat. Suggest to change them for the reasons of energy saving

 

[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.