2 RCDs same circuit

[Big Man]

Am wanting to put in a garage CU to divide up garden and garage lighting and power circuits. Currently power comes off kitchen ring that is already protected with a 30mA RCD. For sake of convienience to client, if mower trips RCD they can flick RCD back on at garage RCD rather than having to move furniture to get to main CU and also effecting kitchen appliaces. Has anyone had problems with problem tripping or test results being wrong. Or am I good to go down this route.

Thanks people.

 

[harrymonkfish]

is it totally seperate or attached? this is still a greyish area about exporting earths. prob best idea is to tt the extension

It will be totally separate. the outbuilding will be TT, the house PME.

If I do it this way am I right that the SWA should only be earthed at the intake to house and not in the outbuilding?

thanks
harry

 

[Guest123]

Hi.

I be looking at a 50A MCB max for the 10mm SWA.

In free air the max CCC for a PVC SWA without applying any correction factors is 60A.

XLPE SWA does have a higher rating but not by much as it's rated to 90 degrees whereas PVC SWA is rated at 70 degrees.

 

[ezzzekiel]

yes dont connect the earth at new end, drop in a rod

 

[harrymonkfish]

The customer has now informed me that the workshop is actually going to be a separate building!

The workshop will just have a ring and lights so quite straight forward.

Can I take the supply from the house to the extension containing the shower, lights and ring, and then take another sub main from there to the workshop?

Or, take 2 SWA cables out to the two locations from small CU at intake with separate MCBs and earth both separately?

Thanks
Harry

 

[electricAl]

You could do it eiher way, Harry. You don`t mention distance from 1st outbuilding to workshop - if close then may be better to submain workshop from 1st D/B.

If using seperate submains for each then obviously TT each seperately as discussed.
10mm or > earthing conductor, & 6mm or > for MEB when TT`ing

As you thought, earth SWA at supply end only - insulate at individual D/B`s (as per 542.1.8)

If you do feed a sub from the 1st D/B then you really ought to consider upping to 16mm. As Lenny intimated, even XLPE would only give you 58a if buried, so you`d have to drop down to a 50a breaker. That`s too low IMHO to class as a well designed install with all the loading possible. A 16mm XLPE submain would offer more than enough to allow that 63a as you`d first planned.

Hope it`s useful

 

[Had8Lives]

The RCD side of things seems to have been answered. You shouldn't really have furniture in front of a CU, it should be easily accessible.