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TT Supply and SPDs for EV Charging point

Got a job to do when the lock down ends.

Customer is having a EV Charging point installed by a 3rd party into his garage, and the consumer unit in the garage needs upgrading (extra way) with a Type A RCD (EVCE has DC monitoring internally) .  Existing supply to garage is 16A and due to the house being rented customer doesn't want to replace the buried cable, so EV Charging Installer is going to de-rate the charger to 3kW.

Existing installation is TT, supplied by overheads and CRL would recommend SPDs are fitted.  Garage is fed from a dual RCD board with Type AC RCDs.

So 1st of all I have to take the garge supply out of the existing consumer unit and protected it was a Type A 100mA time delayed RCD with a relevant MCB (20A).

Now because the supply is overhead I'm led to believe that a Type 1 SPD is required to be fitted at the origin.  One supplier of a Type 1 SPD, recommends that it is protected by a 63A MCB, and also says an RCD should not be installed upstream of this type of SPD as there is potential leakage.  534.4.7 also confirms this.

So I now have to put the following components in a new enclosure (or enclosures), 63A MCB, SPD, RCD and 20A MCB, in that order.  Because its a domestic then these should all be enclosed in a metal enclosure, I assume these come under the 'Switchgear assemblies' definition.  But I am nervous that I would have incoming tails to a metal enclosure that connect to a MCB which then connects to the SPD before we get to RCD protection!

How do I overcome this and keep to the regs?
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  • I might be mistaken but I don't think a type 1 is required unless there's a lightning protection system installed.


    I might be tempted by a SPD that doesn't need an upstream MCB and in a plastic enclosure - e.g. something like https://www.tlc-direct.co.uk/Products/WYREC2SPD.html

    (fortunately such an assembly doesn't meet BS 7671's definition of switchgear or a consumer unit).


    As long as they're connected as connection type 2 (CT2) - i.e. the SPD element for L connects to N rather than PE - they can go upstream of RCDs on a TT system.


       - Andy.
Reply
  • I might be mistaken but I don't think a type 1 is required unless there's a lightning protection system installed.


    I might be tempted by a SPD that doesn't need an upstream MCB and in a plastic enclosure - e.g. something like https://www.tlc-direct.co.uk/Products/WYREC2SPD.html

    (fortunately such an assembly doesn't meet BS 7671's definition of switchgear or a consumer unit).


    As long as they're connected as connection type 2 (CT2) - i.e. the SPD element for L connects to N rather than PE - they can go upstream of RCDs on a TT system.


       - Andy.
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