Getting power to a shed

[Tim Brennan]

Finally made the decision to put in the SWA cable to the shed. One of the electricians that has quoted me has recommended to install separate dual RCBO with enclosure to protect the circuit to the shed (materials required 25m tails x 2mm, 1 x Henley block and 16mm earth cable). He said that it would be best if the shed was on its own RCD because if the cable to the shed trips the RCD often then it will keep knocking out power to half the house.

Just wondering if this is really necessary.

 

[GarryMartin]

You clearly work at the same speed as I do...  [big grin]

Assuming you mean 2m of 25mm [wink], it's actually a neat way of doing it and the way I've discussed doing mine with my electrician. As you've been told, it removes the issue of nuisance tripping of your main RCD in the house if there are issues in the external building.

I actually have a board in the house that's full of RCBOs so it didn't quite make the same difference for me, but getting the SWA to that board (on an inside wall) versus the Henley block from the main fuse entry point (on an external wall) was just much easier. It also means I can easily put in a 230V 16A socket in the garage where the entry point is too, so win win.

Factoring in voltage drop, and assuming 230V, 6mm SWA in PVC or XLPE will cope with a 7-8kW load over that 50m run.

 

[richy3333]

Finally made the decision to put in the SWA cable to the shed. One of the electricians that has quoted me has recommended to install separate dual RCBO with enclosure to protect the circuit to the shed (materials required 25m tails x 2mm, 1 x Henley block and 16mm earth cable). He said that it would be best if the shed was on its own RCD because if the cable to the shed trips the RCD often then it will keep knocking out power to half the house.

Just wondering if this is really necessary.

Hi.

If there is no spare capacity in your existing CU then the main tails can be split to supply 2 CU's. Tail size to the new board will be dependant on the type of earthing system you have at the property.

Re the use of RCBO's in the new board that supplies the shed - in simple terms there is no need for this if using SWA cable. An appropriately sized OCPD is all that's required. Then use an RCD or RCBOs in the board in the shed. If you use RCBOs on the supply circuit and in the shed an RCD, there will be no discrimination over which RCD/RCBO trips in the event of an Earth fault.

I assume the electrician is satisfied there are no extraneous conductive parts in the shed that require bonding?

BTW both new CU's will now need to be metal clad as of January 2016 so the ones previously discussed won't be suitable.

Also check if the work requires notification to BC as per part P of the English building Regs.

HTH