RCD trips

[Mick89]

Hi,

I've just had a garage built, I have laid some armoured cable from the house CU to the garage CU. The garage has a small ring circuit and a lighting circuit. When I was setting it up I just used a household plug on the end of the armoured cable plugged in to a  socket, it all worked well and I was able to check all the sockets in the garage and everything worked ok. When I tried to connect the cable in to the house(main) CU it was all ok but as soon as I put a load on the circuit in the garage whether it be a light or an electric drill the RCD in the house CU tripped, this happens repeatedly and cannot think why this is happening as it’s a very basic set up. There was no load on the MCB I was connecting the cable to and tried it on a number of the MCB’s. I hope someone is able to point me in the right direction.

thanks

mick 

 

[Murdoch]

I’m guessing you are a diyer with no test kit .... so time to call a spark in to inspect, test and fault find ......

nothing else is is likely to help you

 

[Mick89]

Thanks, you guessed it I’m a diyer, only equipped with a multimeter and enthusiasm! Hoped it would be something simple I was missing, will have to look at getting a professional in. Cheers

 

[Doc Hudson]

It is something simple, You failed to do any dead tests before you energised an alteration / addition to an installation. Continuity and insulation resistance tests would have confirmed your problem before attempting to put power onto the circuit.

You never test an alteration by just connecting the power and 'seeing if it works' as this is a potentially lethal method of testing. Get it wrong and electricity will kill a healthy adult in under a second, or start a fire. If you are lucky it may just trip a fuse or melt a bit of cable.

I am guessing this new alteration is also lacking an electrical installation certificate, (and part-p building regulations compliance if in England or Wales)?

Doc H.

 

[kerching]

Well.       If the RCD holds when there is no load connected AND it trips when there is ANY load connected I would hazard a guess that you are connecting to a dual RCD or split load board and you have connected the neutral to the wrong neutral bar. But it's a bit hard to see from up here

but what do I know?   See present wife for further details of a list of my failings

jusr saying

 

[ProDave]

Yes another vote here for neutral in wrong block.  Clearly it shows you don't understand some basic principles so you really should get a professional to check it all.

 

[Mick89]

Hi, 

Thanks for all the advice. I didn’t connect the neutral to the wrong bar, I do understand some basic principles. Thanks for Doc Hudson’s excellent advice, I carried out a continuity/resistance test on the ring circuit. This highlighted a minor issue where I had put a neutral cable to far in and it was secured through the insulation, resolved that, checked the resistance again across all the sockets and reconected to CU, no tripping all working as it should. On the advice of Doc Hudson I think I’ll get someone to check it to ensure it’s all ok.

cant believe such a tiny difference in the resistance was causing it to trip the rcd.
 

thanks again

 

[kerching]

Perhaps someone else can explain to me why this could trip an RCD

 

[ProDave]

No I don't understand that either.  I can see why it would give a broken ring continuity fault but that would not trip an RCD.

 

[Murdoch]

No I don't understand that either.  I can see why it would give a broken ring continuity fault but that would not trip an RCD.

It wouldn’t trip a rcd.

i suspect that fiddling around has “corrected” a fault.

wonder what tester the op has ......

 

[kerching]

Well I cant see what fault it can have corrected as it all worked when a plug top,was rammed onto the SWA.........unless there was no Earth connection made to the plug, just a thought

has the OPS board got RCBOs Or just 1/2 RCDs......?       just curious