Power to the summer house

Look at getting a 5 way board, as opposed to a 'Garage Consumer unit'. There's much more room for the cabling and for future upgrading.

Something like this http://www.screwfix.com/p/wylex-5-way-metal-enclosure-main-switch-consumer-unit/26018

This consumer unit has a 100A main switch which can be used with RCBOs or alternatively swap out the 100A DP to a 63A RCD and then use standard MCB's.

 

Other questions

1) What are the current earthing arrangements at the house side. i.e. TNCS or TT (earth rod)?

2) Is your house end terrace of terrace, how are you planning on routing the SWA from the hosue to Summer hosue?

3) Could ducting be installed inside the trench to export phone line or modem line etc?

 

The 63A RCD would be sited in the summerhouse CU supplying the relevant circuits i.e. lighting and power.

You'll need 1 spare way in your house CU. The SWA would normally terminate in a box near the CU with glands and then be brought into the spare way inside the house CU. The MCB supplying the summerhouse doesn't have to be RCD protected. What board do you have at present? i.e. is it a dual split load RCD (i.e. with 2 x RCDS and a main switch) or just a split load board (i.e. 1 side unprotected ways and the rest are RCD with a main switch?)

 

A picture would be helpful.

 

OK those two can be installed in the summer house, you'll just need to swap the 100A main switch for the 63A RCD.

I am thinking that you would have 2 circuits in the summer house one for power and the other for lighting.

1) A 20A MCB would be be fine for the power side, this circuit would be a radial circuit.
2) A 6A MCB for the lighting circuit.
3) You could also instal an additional lighting for the lighting if you'll be using a exterior flood light, but both can be used on just the one circuit. Just buy a pack of blanks to cover the slots on your CU.

For the loads you have described a 4mm SWA cable would be ample, but I would fit 6mm cable.

 

If you have PME your earthing arrangement is TNCS. The SWA 3cr would be glanded with a lock ring and a banjo ring. Use a length of 6mm earth cable crimped one end and connect with a nut and bolt to the banjo terminal. The other end to the earth bar on CU, this should be done at both ends i.e house and summerhouse.

You will be able to bring the SWA straight in to the bottom of the CU.

 

There are other options. For instance you could come in straight with the SWA directly into a metal clad double socket, disregarding the CU altogether. And then use a FCU downgraded to 3A for your lighting circuit.

The 4mm would very easily meet your needs, but for a small amount (£25) for 6mm. It just makes sure you're protected if ever you put in further appliances later on.

 

Could you provide the ratings in A's for the current circuits you have:

1) Upper ring
2) Lower ring
3) Lighting
4) Shower
5) Kitchen ring

 

I was thinking that the main 63A RCD in house could be replaced with a higher 80A RCD.

This one could then go in the summerhouse CU.

All dependent on what the ratings for the other circuits are.

Just wait until you hear the view of the regular electricians on here.

 

There are only 4 circuits in the CU. Is it possible that all the sockets are on a single 32A? It would be a good idea to label these for reference.

Regarding the CU, an MCB can be inserted into the spare fuseway. The only downside is that when you have the summerhouse CU installed there will be two RCDS in series, resulting in inconvenience should it trip. There will be no discrimination between the 2 CU's.