Tripping Electric


Would really appreciate people’s advice on this one.

I have the following system:

NAC282 with NAPSC

I have recently converted a garage with dedicated mains spur with a Castelec consumer unit. The RCCB is a 100mA 80A with B type circuit breakers.

The main consumer unit in the house feeding this the make and model is unknown.

Problem I have is on switch on of all the electronics everything powers up fine but around 50% of the time the 250DR trips the electric main RCCB switch on the garage consumer unit (not the MCB breakers). Also tripping is the “RCD Controlled Circuits” switch on the house consumer unit but the Main switch labelled “Garage outhouse” on the house consumer unit doesnt trip (B40)

All the electronics are powered into an 8 way power block (due to number of power sockets available), with the exception of the NAP250DR which is powered straight into a wall socket.

I have an electrician who installed all the garage electrics and consumer unit who thinks it is earth leakage but he isn’t convinced and unsure of what to change.

Has anyone else experienced this before? Very frustrating to say the least. I know there are some posts explaining MCB B typr breakers tripping but in my case the breakers dont trip.

Any help/advice is very much appreciated.

Kind regards,

No experience of this, but it does sound as if there might be a momentary/slight earth leakage during the 250 switch-on operation, but what the mechanism of that might be I can’t picture. If it is tripping the house RCD as well, try the 250 plugged into a house socket (multiple times). If that doesn’t trip at all then it becomes more of a mystery

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First thing I would change is the type B circuit breaker.
These are not good for heavy inrush currents at power up such as we have with transformers.
Type B trips between 3 and 5 X rated current
Type C is 5 to 10 X
Type D is 10 to 20 X

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Yes I have heard of this on the forum before and thanks for your reply.

I mentioned this to the electrician who keeps insisting its nothing to do with the breakers as they aren’t tripping so he seems to be ignoring this possibility

Kind regards,

My gut feeling is the same as the electrician’s, hence my thought and suggestion above.

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Thanks for your reply

It doesnt trip the main switch on the house consumer unit, only the switch labelled “RCD Controlled Circuits”


Kind regards,

It sounds like you have taken a slot in the main consumer unit and run the garage circuit from that. Best practice is to split the meter tails and run live, neutral and earth all via their own separate consumer unit.

Following Naim’s advice to keep all units powered up would obviously reduce the frequency of this problem, although I understand why people are increasingly reluctant to do so these days.

As Chris says, you should split the meter tails rather than running off the house CU. The hifi CU earth should be run direct to the meter, and not piggy back off the house. Type C breakers in the hifi unit should then solve the problem.

If I understand you correctly, you are suggesting running a mains cable between the house and the garage without any fuse protection on that cable.

I certainly wouldn’t be doing that.

Or have I misunderstood your suggestion.

The separate consumer unit would be near the meter, not in the garage, so the cable would be protected.

ELECTRICIAN: Going to have to move the breaker off of the rcd and change it to a type c rcbo and put a main switch in the garage
ELECTRICIAN: That’s the easiest and quickest way mate
ELECTRICIAN: Will sort price out today

This is what the electrician is now proposing. Any advice is very much appreciated and thanks forneveyone who has replied

Kind regards,


Thanks to everyone who has replied

Kind regards,

I agree with him that removing the garage circuit from the RCD in your consumer unit would likely sort the problem, and a type C RCBO should prevent nuisance tripping when you turn on the HiFi.

I would still split the meter tails and add the separate consumer unit close to your main one if you can be bothered, but that is not the ‘easiest and quickest way’.

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I agree makes sense.

Just trying to work with the electrician and not question his expertise to the point of peeing him off!

But will suggest it to him.

Kind regards,

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Good luck!!

Thanks and thanks again for your input

Kind regards,

You go to a restaurant for a nice meal. You order a bottle of Brunello. The waiter says, sorry mate, it’s at the back of the cellar. It would be far easier for me to give you this bottle of Chianti that’s under the bar.

Remember who is the customer here, and that the electrician’s role is to meet your requirements - so long as they meet the regs of course - and not to do what’s easiest.

What you want is this. Show him the pictures and ask him to do it. If he refuses, go elsewhere. Remember that the rails are split with the mains live and the electrician standing on a rubber mat. If he’s not comfortable with that, again get someone who is.

Not sure that I could work with an Electrician like that… :thinking:

Quickest & Easiest, ‘Mate’…??


To be fair, when the electrician gave those replies, he probably hadn’t been asked to do anything other than solve the problem of the tripping RCDs.

You wouldn’t go criticizing a waiter for not bringing a bottle of Brunello, when he hasn’t been asked to bring a bottle of Brunello. Yet.:sunglasses:

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My comment was based on my perception of the Electrician…