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rcd tripping with power cut


paul b b

Question

hello chaps,

I have to see a customer with various snags.

1 is that her rcd trips when she has a power cut, I have not seen the cu as yet but will say its a TT with 100ma s type as a main switch as she lives in the sticks.

My question is why would this happen and is there a way of stopping it?

many thanks

Paul

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21 answers to this question

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ok, i have seen the job now and i pressed the trip button (80a 30ma rccb) and then switched it back on, it would only do this if all breakers are off the switch rccb back on then switch all breakers back on.

any ideas?

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Had a similiar situation the RCD went at the slightest thing, and would only reset with the breakers off, isolated by switching various breakers in and out and trying to reset, found that everything was fine until the Kitchen ring was added, in the end found the problem was a faulty kettle.

My explination which may or may not be right, was that the kettle combined with items on the other circuits using a functional earth were enough to cause the RCD to trip on in rush, but where right on the edge when brought in bit by bit.

Hope this helps

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ok, i have seen the job now and i pressed the trip button (80a 30ma rccb) and then switched it back on, it would only do this if all breakers are off the switch rccb back on then switch all breakers back on.

any ideas?

Probably break down of insulation on circuits and even a fault as said the best way to get over this is with a new dual board although I go for Rcbo's generally these days. I would test RCD (ramp test) with nothing connected to see if its ok.

Batty

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Probably break down of insulation on circuits and even a fault as said the best way to get over this is with a new dual board although I go for Rcbo's generally these days. I would test RCD (ramp test) with nothing connected to see if its ok.

Batty

when you say nothing connected do u mean unplug everything?

i have never done a ramp test, what results would i be looking for?

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On the ramp test you are looking for the ma at which the RCD trips, if this is considerably lower than the rating of your RCD (30ma) it may be that the RCD is over sensitive.

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What kind of loads are usually connected to the installation ?. I understand that some appliances eg, computers or inductive loads can allow small amounts of current to leak to earth so perhaps if appliances such as these were all starting up together rather than being switched on at different times then that could potentially trip an RCD.

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when you say nothing connected do u mean unplug everything?

i have never done a ramp test, what results would i be looking for?

You can do it at the consumer side of the Rcd with fuse box off. You need tester which can do ramp test. It will show at what mAmperage the Rcd is tripping out at, if its less than 15mA its classed as faulty. Hopefully it will be around 24mA.

Batty

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so would have to change rcd. though this one is an RCCB what if any is the diferance?

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so would have to change rcd. though this one is an RCCB what if any is the diferance?

Same thing probably to an old British standard 4293 although you would need to read up on testing them. Some older ones are treated differently.

Batty

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Question is does it trip when the power goes out (i'e' rcd isn't staying on when not energised) or as Revved said, is something tripping it when power is restored?

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thanks batty, would u fit 1 now though, i have seen them for sale but always stayed away from them?

back to it though, if i fitted rcbos is it likely to solve the problem? and would this be a MW cret or EIC cret.

many thanks

paul

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thanks batty, would u fit 1 now though, i have seen them for sale but always stayed away from them?

back to it though, if i fitted rcbos is it likely to solve the problem? and would this be a MW cret or EIC cret.

many thanks

paul

To comply with regs you cannot have one RCD to control whole installation. I like RCBO route as you only get problems on one circuit if there is a problem with installation. But customer has got to agree to pay extra although I usually persuade them its the best option.

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To comply with regs you cannot have one RCD to control whole installation. I like RCBO route as you only get problems on one circuit if there is a problem with installation. But customer has got to agree to pay extra although I usually persuade them its the best option.

this place was wired about 10 years ago, though i think the last owner had the same problem as the neighbour used to pop in if they were away and switch the rcd back on.

If i install rcbos should i change the main rccb for a standard main switch? and do i have to test all circuits?

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this place was wired about 10 years ago, though i think the last owner had the same problem as the neighbour used to pop in if they were away and switch the rcd back on.

If i install rcbos should i change the main rccb for a standard main switch? and do i have to test all circuits?

Is the rccb in the board or a seperate one?

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in the board as the main switch

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I would imagine its probably an old RCD and probably not s type. I have had this the only way to get over it is fit a new consumer unit with modern RCD's as they are not so prone to tripping out after power cuts.

Batty

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what test would i do to find this out?

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in the board as the main switch

Probably best to change board then. You would need to check earthing, are they circuit breakers if so you could get away with not testing although it would be a good idea to test the installation as it sounds like there may be problems. How many circuits are there.

Batty

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ok thanks, batty.

is it likely to solve the problem if i change the board, if so i will try to talk her in to a change.

thanks

paul

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ok thanks, batty.

is it likely to solve the problem if i change the board, if so i will try to talk her in to a change.

thanks

paul

If she has got a fault it won't solve that but if you go RCBO route it will narrow it down to one circuit but hopefully you will find fault when testing circuits. I have just changed three boards in London. There where quite a lot of faults on these mainly open and a few neutral to earth faults on socket circuits. The lighting circuits all had quite a lot of break down of insulation on them some as low as .5 mohms but as I have used RCBO'S they have not tripped out yet.

Batty

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If there`s an isolator upstream, try knocking that off. If the RCD trips, it`s non-latching, and needs to be changed to prevent this happening.

If there isn`t an upstream isolator, try swapping out the RCD and see what happens on the next power cut?

HTH

KME

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