Garage Consumer Unit

[JM9]

Hi,

A friend had a new outside garage built which required an electrical supply. He has installed a ring main in the garage for sockets and a radial circuit for the lights. This has been connected to a 4 way garage consumer unit with a 40A 30mA RCD with a 32A and 6A MCB's. The garage consumer unit has been connected to the main consumer unit in the house via 28 metres of 3 way 6mm SWA cable. The SWA is connected directly into a 40A MCB on the consumer unit via a metal junction box. The 40A MCB has been situated next to the main on/off switch for the consumer unit on the non RCD side of the consumer unit. The SWA has been connected directly into the plastic garage consumer unit. When he tries to switch on the RCD in the garage it trips immediately, does anyone know why this is happening? The SWA cable is live and he has used the earth tags on the internal glands for the plastic consumer unit and metal junction box and has used 6mm earth cable for this.

Many Thanks

 

[Paul.M]

Have you tested the swa? Faulty isolation switch? Wrongly wired N at the garage cu? Fault on one of your circuits in the garage? Faulty rcd?

 

[JM9]

Garage unit is ABB. Wired as per instructions with unit including the neutrals. SWA cable is live. RCD trips even with 32A and 6A MCB's switched off. When try to turn it on, it trips as you try. Circuits in garage are fine. Suspect that the RCD is faulty?

 

[Paul.M]

What were the IR readings on the new swa?

 

[diditrain]

Neutral of the SWA in the wrong neutral bar in the main D/B.
Did your mate terminate both ends of the SWA. Do the colours match up at both ends

 

[Octopus]

What tests have you / your mate done? Its difficult to make too many suggestions without knowing what's been investigated.

 

[nickblake]

With not knowing much about the garage install its self only the armoured side then it should be an idea to recheck the garage wiring , this fault could be a fualty RCD or a trapped neutral in a socket polarity of the neutral and earth incorrrect , what you could do is disconnect the out going of the RCD in the garage and try switching the RCD on again , but it sound to me as if the is a neutral and earth with their terminals reversed so the neutral is connected to an earth some where have a look at the lighting ,

 

[kung]

Should be fairly easy to find fault with test gear that needs to be done as the supply cable is a distribution cable and needs an EIC so will need tests done that should show up where the fault is. Might be a damaged cable eg whilst install cable clips hit cable ! or wrong connections as said ! is your mate registered with a scheme provider ? if not this will need notifying to LABC ideally before power up.

 

[Deleted member 9648]

IR test the garage circuits.........that is always the first stage of any fault finding exercise like this,otherwise you are just guessing.

 

[truckster]

It must be the garage wiring as an RCD won't pick up fault upstream unless it has neutral sensing such as the Mem ones with the little white wire that goes to earth. Also have you checked polarity?

 

[Big n Daft]

Disconnect and IR test the garage circuits one by one.
If that cant be done get a qualified sparks with a megger. Its only a garage so it should take about 15mins to find the fault.