Sub-main to the garage in house I just bought

[DoubleInsulated]

Hello all.

17th edition sparky here, but not been on site for the last 3/4 years (had a bit of an accident).
Just bought a house with a 16mm 3 core SWA, 15m long, clipped around the side of the house low level. This feeds the double garage.

It has it's own 100A fused isolator in a kitchen cupboard (behind the meter box) with a 63A HRC fuse in it. 25mm tails (16mm earth) come from a couple of DP connection blocks in the meter cupboard.

Garage end has a 12 way split load metal DB with 2x 63A RCD's and is only feeding a couple of sockets on a 16A radial and the lights on a 6A.

My question. Not being up to date now on the 18th, should that external SWA sub-main be protected by an RCD?

Reason I am asking is I want to have a car charger added to the garage and that has it's own internal RCD (They are fitted by a local company as part of the car purchase deal). The board in the garage would be re-arranged so that a 32A MCB would be after the main switch (not on the split load).

Thanks from a slightly broken old sparky

 

[Lister1987]

Without knowing thr age of the house it'd be hard to say, I think RCDs on everything was recent (2018) if so yhrn you've got the "Complied at time of erection" argument.

Either whack an RCD on the garage circuit in thr main board or leave it off an RCD in tht House and put a Type A in at the garage end, although Check your EV kit manual as they may want a different setup.

Still Lear ing so happy to be corrected

 

[SparkyChick]

Unless I'm much mistaken, no it doesn't need an RCD on the SWA submain. The SWA has earthed metallic covering which is one of the factors that negates the requirement for RCD.

533.6.204 (i) incorporate an earthed metallic covering which complies with the requirements of these regulations for a protective conductor of the circuit concerned, the cable complying with BS 5467, BS 6724, BS 7846, BS 8436 or BS EN 60702-1, or (one of the other conditions).

So providing the armour is properly earthed, no problem.

 

[westward10]

Unless it is required for fault protection.

 

[timhoward]

The only circumstances I can currently see it needing an RCD for fault protection would be if the house had TT earthing.
15m of 16 sq mm SWA wouldn't otherwise have a problem with the fault current failing to blow a 63A fuse.

 

[westward10]

The only circumstances I can currently see it needing an RCD for fault protection would be if the house had TT earthing.
15m of 16 sq mm SWA wouldn't otherwise have a problem with the fault current failing to blow a 63A fuse.

Maybe your Ze is 0.80 ohm

 

[timhoward]

Maybe the answer should be that to be sure get someone to do a loop test!

 

[Dave OCD]

Even if the Zs is sufficiently low not to require additional protection it wouldn't do any harm to install a 100ma S type RCD at the switch fuse end, just in case of failure of the downstream RCD/s.

 

[westward10]

Even if the Zs is sufficiently low not to require additional protection it wouldn't do any harm to install a 100ma S type RCD at the switch fuse end, just in case of failure of the downstream RCD/s.

If we worried about devices failing we would be backing everything up.

 

[Dave OCD]

I'm not worried at all, just thought in your own home it's nice to go a bit 'belt and braces'....