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Looking for advice regarding TT garage sourced from TN house

Glidos

I've just had an EV charger installed, and taken the opertunity to have my old fuse box replaced with a new consumer unit, and the garage properly wired with a submain. The house is TN and the garage now TT. The SWA is sourced from an MCB. I've realised that there's one unlikely but very nasty fault that isn't well protected against. If the SWA live tail, coming into the garage CU, somehow made contact with the body of the CU, there wouldn't be enough current through the earth rod to trip the MCB at the house and the fault is the wrong side of the RCBOs in the garage. The body of the car, if plugged in, would go live. Any thoughts on this?

  • 0

    This is the classic problem of TT supplies - and why in my personal opinion the first RCD should be in a plastic box and no CPC brought near it if at all possible
    However, it may be that by cunning use of compression glands and maybe additional insulation, it is not credible for the pre-RCD cable to come loose and to touch the metal box. I presume the SWA armour is on the house earth, so any accidents with garden forks etc will trigger the MCB. If not then the RCD needs to be at the house end.

    regards Mike.

  • 0

    See if the manufacturer of the garage CU offers a specific kit for connecting TT tails to the main switch.  It will be designed to prevent the incoming supply coming adrift.

  • 0 in reply to mapj1

    Yes, the SWA armour is on the house earth. I guess it is, as you say, an extemely unlikely fault.

  • 0 in reply to Simon Barker

    Thanks, I'll look into that.

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