Summer House / Office - MCB's and consumer unit help

[lifetimesmile]

Hi All,

I hope someone can help, I'm planning on running power to my summerhouse some details:

55-60meters away from the consumer unit
the power will have to be 2 computers, TV and hifi (i'm thinking 6 double sockets)
2 x five-foot twin Cat 2 fluorescent's
1 x 2.5 or 3kw heater

I'm thinking of using 10mm2 SWA from the house consumer unit to the summer house where i'm planning on putting another consumer unit (recommendations?) and from there run 1 x 32a MCB for the plugs, 1 x 6a MCB for the lights and another 32a MCB for the heater?

what should i put in the house consumer unit?

Hope this all made sense? Any advice would be appriciated

Many thanks in advanced

Smiler

 

[Chri5]

A 10mm SWA will have a 4% drop over 60m and take a max load of 32a, which is about 7500 w or 7.5 Kw

I'd suggest that 32a is acceptable and that you provide an MCB via an RCD or a RCBO rated at 32a.

At the summer house end buy a small builder or garage CU rated at 32a and then have 6a fuses for lights and 20a radial for sockets. With diversity you could get away with a 32a ring, but I suggest de-rating since 20a should be fine and won't cause overload issues on the cable or back at the house CU with a 32a MCB or RCBO.

One of these would do http://www.tlc-direct.co.uk/Products/TLBS32slash6.html, although I'd dump the 32a MCB and go with a 20a for the sockets

 

[lifetimesmile]

So don't bother with a seperate ring for the heater? just stick it all on the 20A?

Thanks

 

[Steve]

Chris, I'd advise against a builders unit. A 4-way CU would be far better, with an RCBO for the sockets. The heater and lights can have their own circuits too.

5 way board:
http://www.tlc-direct.co.uk/Products/WYNH504.html
6 amp MCB for lighting:
http://www.tlc-direct.co.uk/Products/WYNSB06.html
16 amp MCB for heater FCU:
http://www.tlc-direct.co.uk/Products/WYNSB16.html
32 amp RCBO for sockets:
http://www.tlc-direct.co.uk/Products/WYNSBS32slash2.html

The feed from the house should no NON RCD protected.

 

[lifetimesmile]

Thanks i'll go with a larger unit and have the 3 supplys plugs, heater and lights. would it be advisable for a slightly larger cable than 10mm?

 

[Chri5]

I was working on an assumption that 7500w of total load would be pretty difficult to overload.

Also assumed that the heater wouldn't be on for more than 5 months a year and only short bursts of full power. If you work to an example of 1500w of use on the heater, that's 6000w to take the rest of the loads.
I can't think of anything that might get close to using that capacity.

16mm is the next size up and costs + 90p a metre (2 core SWA) and at the distance you mention will take a 43A load.

Since you have 90% of the work as a dig, it might be better to super size the cable- your choice really.

 

[lifetimesmile]

Thanks for your help guys. So here's my conclution / shopping list.

3core 55>60meter armoured cable so i can earth it to the house's earth
32a MCB in the house (in the non RCD protected side?)
5 way board with:-
- 6 amp MCB for lighting
- 16 amp MCB for heater FCU
- 32 amp RCBO for sockets

and then obviously all the boxs and sockets + 2.5mm cable for the internal electrics.

Is there anything else i should take into account?

Thanks again for all your help

 

[Chri5]

You can use (and should use) the SWA armour as the earth- hence 2 core with the earth being taken via glanding the SWA correctly.

 

[lifetimesmile]

thanks chris will look into this now and 2 core is a cheaper option so even better!

 

[lifetimesmile]

just a thought the armoured cable i use the armouring as the earth should i attach the armouring(earth) to both the CU's house and summerhouse?

Thanks again for all your help guys.

 

[Adam_151]

What is the earthing system in the house?
Any ECPs in the summer house?
What materal are the CUs?

 

[ricicle]

Use a 3 core 10mm² SWA and use the third core as the earth.Then you have no problem with bonding any services (should they be installed) in the outhouse if your main house is PME fed.

 

[lifetimesmile]

Earthing is something i'm not to sure about any tips on how i can find out the kind of earthing system? I know it is just earthed throw the suppliers cable that runs into the property. As for the summer house there is nothing except a stud wall no earth rod and the house has a standered domestic hager unit.

 

[lifetimesmile]

ricicle are u suggesting not to use the armouring as the earth and just as normal to the unit using the 3rd core?

 

[comms]

If the link works here is some reading with regard to the swa armour used as the cpc (kindly posted by John P at sparly heaven).

http://uk.msnusers.com/SparkyHeaven...and Earthingby John Peckham version Jul06.pdf

Me over that distance I'd TT the summer house supply & not export the pme, I'd use 10mm or 16mm 2 core swa & use the armour as the submain cpc (cut cost of cable)............but thats just my preference