Garage unit trips house consumer unit problem

P

porticoman

I'm installing a garage unit but it's tripping the (20A) house breaker. There's no load on the garage unit so I'm missing something obvious/doing something stupid. The garage has pre existing T and E powering lights and a couple of sockets which I want to modify to get a bit of practice after doing Part P. The Wylex 2 way unit (1 x 6A and 1 x 16A) and a RCD is connected as per the instructions (yes,I've read them!) Line/Neutral into the RCD, CPC into the Earth bar and the pre installed neutral link is in place. I've checked the connections to they are biting the conductor not insulation, tight etc. When it's returned back to its original format (no garage unit) it works perfectly so I'm being dense and maybe not asking the right question. Anything constructive suggestions the forum could add would be great.

Thanks

Peter
 
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Might seem obvious, but when you put the L/N into the RCD did you make sure they were the right way Round ? You could try just fitting the 2 way in the Garage with no Circuits connected & see what happens.
 
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porticoman said:
I'm installing a garage unit but it's tripping the (20A) house breaker.
Click to expand...

Hi, I read that to mean it's tripping the MCB, is that correct?

Is it tripping, even with the RCD switched off in the garage? Have you tested the submain, and did the results seem satisfactory? What is the earthing arrangment out of interest? Can you check the cable feeding the garage physically for damage?

Rich
 
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Bimey, that didn't take long. Yes it's SWA. There's nothing connected to the unit at the moment, I did try it with a radial final attached, but it tripped. I disconnected it to see if it was part of the original installation or something I'd done wrong. Sadly it was the latter of the two! It's currently restored to its original state (without garage unit) and is working fine.
 
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What is tripping the mcb or the RCD? Whichever you need to test the sub main the garage from the house end, with L&N disconnected. Test for polarity and IR. If that tests ok then come back to us!
 
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This is a perfect example of why an electrician connects up a new or modified installation, they conduct a set of "dead" tests to establish all is as it should be, before going live.
 
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Dunx, will do...thanks very much

The earthing is TN-S

I didn't test the sub-main. In my head the reasons were: I knew it was working and I wasn't adding extra load. In my head was obviously wrong... curse you Inside Head.

The SWA isn't earthed at the garage end. Should point out I didn't put it in!

There's some useful stuff in these replies, even the wrist slapping ones!

Ideally I'd like to have done the learning in conjunction with an experienced electrician but despite a letter writing campain no one seemed interested. Training courses just don't cover it. Sadly the only other avenue left open is to be a dangerous idiot for a while and rely on forums etc to sort out issues. Not really the way I like to go through life, so thanks to all respondents.

As an aside, as a plumber, we find that when electricians are working in premises they tend to switch the boiler off from the consumer unit along with everything else. This causes a nuisance lock-out of the boiler because water stuck in the heat exchanger continues to heat up for a few seconds after the boiler shuts down (the power to the pump having gone means it can't pull new cold water over the heat exchanger). Low water volume boilers can reach very high temps very fast, resulting in a safety cut out activating Shut it down by the programmer, switching the hot water and heating off a minute or two before cutting the power. This phased shut down allows the pump to over-run and carry the excess heat away. Happy days for the customer...

Thanks

Peter
 
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Dunx said:
My thoughts were to start at the beginning...sub main first, then load circuits.
Click to expand...

Yes I realise that mate, but according to the OP everything worked ok in the Garage until he disconnected whatever box was there originally & put the 2 way CU in it's place. He's removed the CU now & put things back how they were, i.e with the lights & sockets back on & no more tripping of the MCB. From what he's said so far i'd guess the feeder is ok otherwise he's still have a problem & the problem is something he did, in fact he did actually say that earlier.
 
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porticoman said:
I'm installing a garage unit but it's tripping the (20A) house breaker. There's no load on the garage unit so I'm missing something obvious/doing something stupid. The garage has pre existing T and E powering lights and a couple of sockets which I want to modify to get a bit of practice after doing Part P. The Wylex 2 way unit (1 x 6A and 1 x 16A) and a RCD is connected as per the instructions (yes,I've read them!) Line/Neutral into the RCD, CPC into the Earth bar and the pre installed neutral link is in place. I've checked the connections to they are biting the conductor not insulation, tight etc. When it's returned back to its original format (no garage unit) it works perfectly so I'm being dense and maybe not asking the right question. Anything constructive suggestions the forum could add would be great.

Thanks

Peter
Click to expand...
so you`v become part p registered.....now you want to "get a bit of practice in" sorting out a lighting circuit in a garage?....hmm....
 
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porticoman said:
Dunx, will do...thanks very much

The earthing is TN-S

I didn't test the sub-main. In my head the reasons were: I knew it was working and I wasn't adding extra load. In my head was obviously wrong... curse you Inside Head.

The SWA isn't earthed at the garage end. Should point out I didn't put it in!

There's some useful stuff in these replies, even the wrist slapping ones!

Ideally I'd like to have done the learning in conjunction with an experienced electrician but despite a letter writing campain no one seemed interested. Training courses just don't cover it. Sadly the only other avenue left open is to be a dangerous idiot for a while and rely on forums etc to sort out issues. Not really the way I like to go through life, so thanks to all respondents.

As an aside, as a plumber, we find that when electricians are working in premises they tend to switch the boiler off from the consumer unit along with everything else. This causes a nuisance lock-out of the boiler because water stuck in the heat exchanger continues to heat up for a few seconds after the boiler shuts down (the power to the pump having gone means it can't pull new cold water over the heat exchanger). Low water volume boilers can reach very high temps very fast, resulting in a safety cut out activating Shut it down by the programmer, switching the hot water and heating off a minute or two before cutting the power. This phased shut down allows the pump to over-run and carry the excess heat away. Happy days for the customer...

Thanks

Peter
Click to expand...
oh i see......its OUR fault now.....
 
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Dunx said:
Yup just re-read it but I would still have started at the beginning!!
Click to expand...

OK mate, but why: After being told the same by a customer out on site, the first thing i'd have been looking at was what had changed i.e the New consumer unit & how it had been fitted.
 
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Dunx said:
Cos from there you can test everything....
Click to expand...

But you already have part of the Answer, the system was working OK on the supply cable as fitted, without blowing the MCB. ergo no fault, CU gets fitted & MCB trips out, CU gets removed & original wiring reconnected no tripping. To cut down fault finding time go to CU & shut off, if MCB stops tripping then fault is on CU or internal wiring, if MCB still trips then fault is on supply side or connections & you've narrowed things down without even opening your meter.
 
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It must have a fairly low resistance short to knock the 20A MCB out, I suppose it is possible the garage DB is faulty in some way (is it new?).

or the OP has put the comb section across both RCD terminals.
 
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so did you conduct dead testing to ensure that this circuit feeding the garage was good for continues service BEFORE undertaking any work here?......and what about both earthing and bonding n all?....check those BEFORE undertaking ANY WORK here?.....have you even got test equipment?...because i get the feeling you aint.....
 
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I allways believe what the customer tells me until I can prove otherwise, which i've gotta say has'nt been that often. But even if the customer has got it wrong, if you turn off the CU to start with & see what happens you can save yourself time. It's a common thing in Industry, you split the problem area into smaller chunks so you've got less testing to do & less downtime of equipment.
 
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spark 68 said:
It must have a fairly low resistance short to knock the 20A MCB out, I suppose it is possible the garage DB is faulty in some way (is it new?).

or the OP has put the comb section across both RCD terminals.
Click to expand...

Yep System ok until he fitted a new DB & is ok again since he's removed the DB.
 
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so...on the assumption that this "electrician"..lol.......electrician has got the relevent test equipment to verefy his work....would be interested to know if he has results such as a Zdb for this "install"?.....and he clearly doesn`t know how to fault find either as if he did then he would know that to break up a circuit into portions (point to point) and then dead test...is the way here.....will be something in that garage board or something disturbed in the circuit/s it is feeding as it was ok before....cant see it any other way....divide and test here....
 
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Richard Burns said:
If tripping the 20A breaker (instantly presumably) with nothing connected to the new CU then there is a fault at the new CU that is connecting Line to either neutral or earth (or both). [If there is RCD protection at the house (shouldn't be, unless it is S type for discrimination) and that RCD is not tripping then the fault is Line to Neutral.)]
Make sure it is wired as in the right hand side of the diagram below (the first neutral terminal will not be there), and check that there is not a break in the SWA Line that maybe touching the case as it enters the CU (if it is metalclad).
View attachment 9787
Click to expand...
yes but dont do it for him richard mate......if he cant get his head around stuff like this....then he`s got no business installing...period........makes me cross this kind of thing..(not you mate ...him)....taking money for work done that aint right....it aint on either......:nonod:
 
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Garage unit trips house consumer unit problem
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