Neutral Earth Continuity

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New member
Nov 16, 2020
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I’m rewiring my garage (not physically connected to my house - SWA supply cable running under the drive way)  in preparation for it to be converted to a room. Fed from a garage CU with 40A 30mA RCD circuit 1 is a 6A radial circuit for 3 x outside lanterns, 6 x LED spot lights and a suspended LED panel. Circuit 2 is a 32A ring main with 5 x double sockets. I’ve run all of the cables and continuity tested them without the supply cables connected to the consumer unit, they all test okay so no issues. The room hasn’t been boarded out so I just wanted to connect the outside lights temporarily. As soon as I connected them and turned on the MCB the RCD tripped, I immediately thought that there could be. Fault in a lamp so disconnected them one by on, each time I disconnected a lamp I tested and the RCD tripped. No lamps are connected and it’s fine, 240V through the switch common to L1. I tested for continuity again, this time in the consumer unit and to my surprise found the Neutral and Earth at 0.3ohms. I disconnected the supply cables from the house consumer unit and tested the outside light cable from the consumer unit to the switch and this was fine. I tested the supply cable from the house again and saw the same 0.3ohms from neutral to earth - I assumed a cable fault on the cable under the drive way but could see how it could have happened. I went into the house and tested across the neutral and earth terminal bar and saw the same 0.3ohms, the power in my house seems fine, all of the lights and sockets work and I don’t have MCB or RCD tripping issues. I disconnected the live, neutral and earth cable supplying the garage from the house consumer unit and tested again, expecting to see the fault on the cable with the same neutral earth continuity but the cable was fine. I tested again in the house consumer unit on the terminal bars and saw that the neutral and earth still had continuity.

 I’m completely puzzled, before I started this there was a very simple arrangement with the outside lights and an LED strip light fed from a 6A breaker and a single double socket fed from a 16A breaker, I’ve never known the RCD to trip. Has anyone seen this before, I’m sure it’s not normal to have this Neitral Earth continuity. Sorry for the war and peace, just looking for comments before I start disconnecting circuits one at a time in the house consumer unit to find the circuit that has the IR fault. Thanks 



"It Just Is"
Feb 13, 2012
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Here There and Everywhere
What is this room to be used for? As strictly speaking it will require planning permission as it is a change of use, which may well require building regulations other than part p? Any works carried out would need to be compliant to both requirements  and the electrical works will need to be signed off by a professionally qualified electrician who is registered to a Part P scheme. 

you are also risking yours and your family’s safety by interfering with an installation when not competent to work on it. 
my best advise is to do it properly or not at all, your family will thank me later. 



Trailer Boy - Electrician.
Mar 28, 2008
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Has anyone seen this before.

Yes frequently..

Someone not carrying out full dead tests before energising a circuit..

Then finding it doesn't work when they turn the power on. 

To sound amazed that there is a continuity between N & E at the house consumer unit, suggests you don't understand how the supply comes into a property..

Testing back at the house to try and fix an RCD tripping at the garage CU again shows someone woefully out of their depth!

I would think a competent person with the proper test gear would have this resolved quicker than they could drink a mug of tea.

You describe doing continuity test and saying they were ok..

But what are the actual circuit test meter values that you are going to write on the electrical installation certificate...

(And are you notifying the work for Building Regulations Part-P compliance..  or expecting someone else to do it?)

As rather than just saying you have tested something and its ok..

Better to give all of the test readings you have written down,

so that we can have a better idea of where you have messed up your wiring..

As.. If it was all ok..  you wouldn't have the problems you describe..



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