Garage electrics

[Dodgy]

Hello.
Could do with some advice please!
Have just had two timber buildings added close to house.
Initially planned on using spare way on RCD side of CU with 20A MCB to feed new 45A 2-way 30mA RCD unit via 4m of 4mm SWA T+E, and from 16A MCB there max 10m of 2.5 SWA T+E into second building and second RCD 2-way unit.
Cables laid already. No pipework to bond, armour to be bonded at glands at all ends via earth core back to main CU.

At this stage only nominal loads expected (couple of striplights and 4 sockets in each building, running tool chargers, occasional garden tools etc).

Since laying cables I have had to move leaky cooker circuit to non-RCD side of CU, leaving a second spare way available on that side. As nothing is terminated yet I still have sufficient cable to run the 2.5 straight to the 2nd spare way if this is preferable to the above, though it will be more hassle and I'll have no spare ways left should I need one.
Should I do this, or is the above adequate and safe?
Thanks for any advice.

 

[industryspark]

i would probably go with having one mcb for each buildings supply. less chance of overloading if they are seperate and also if you get a trip on the breaker for the first method you lose power to both buildings which isnt very good.

 

[RF Lighting]

Also you dont need all those RCDs.

You should only have one RCD protecting a circuit. As you planned to do things you would end up with three RCDs protecting the final shed, with no discrimination between the devices.

Also it is best to keep RCD protection as local as possible, and a good idea for the lights to remain on if the RCD trips.

 

[Dodgy]

Ok, so straight back to the non-RCD side of CU for each with own MCB, RCD only at the far end?

I thought I needed to RCD protect the external cable...

Thanks for your advice.

 

[jj4091]

You would protect the cable with the mcb at the CU, you only need to protect the cable against overload & provide a means of isolation.

 

[Steve]

Dodgy, the only thing in the entire installation that requires RCD protection is the socket outlets. I would just have a main RCD in the first outbuilding, protecting both buildings. This is plenty, and protects the lighting too (not required, but unless you have money to burn its the best option . . )