Outside Power Distribution

[slup]

Hi

I know there are a lot of threads on these subjects, but I have some rather specific questions that I would appreciate advice on.

A bit of background:-

Our property is built on a hill. About half way down the garden there is a retaining wall 1.8M in height. There is a summerhouse at the bottom of the garden, and a garage about half way between and offset to the side.

Presently, the garage has no electricity supply and the summerhouse was fed by a length of unprotected 4mm T&E which I have subsequently removed.

Future plans include the installation of a hot tub in the lower level of the garden.

Here's a sketch...

Untitled

• slup
• 8 Aug 2008
• 1

What I am proposing to do is run SWA from the consumer unit at the front of the house as far as the retaining wall. At that location, I would ideally like to install some kind of enclosure containing:-

1) MCB for Summerhouse submain
2) MCB for Garage submain
3) RCBO for hot tub
4) RCBO for garden lighting

My two questions are:-

1) Can you recommend a suitable enclosure, or is my idea flawed
2) Would you mind assisting with the cable sizing?

Load wise, I am anticipating the following:-

Summerhouse:
1 x Double Socket via 16A RCBO
1 x Lighting Circuit via 6A MCB

Garage:
1 x Double Socket via 16A RCBO
1 x Lighting Circuit via 6A MCB

Hot Tub:
1 x 32A CEEFORM socket fed from a 20A RCBO

Garden Lighting / Pond Circuit:
1 x 6A RCBO

Could someone help explain the allowable values for discrimination. For example, in the case of the submain feeding the summerhouse, can I use a 20A MCB given that the summerhouse will contain a 16A MCB - or does the discrimination need to be larger.

Finally, with regard to cable sizing, would the following logic be correct.

Feeds for summer house and garage: 12M at 20A using 3 core 2.5mm XLPE would give a voltage drop of 3.84V so that should be acceptable.

Feed from CU to garden distribution enclosure:-

20A (summer house) + 20A (garage) + 20A (hot tub) + 6A (Garden Lighting) = 66A. 66A over 15 metres would require 16mm cable which I'm not too keen on for obvious reasons!

Have I done something wrong? Is there a way of optimising this arrangement so that I don't need to use 16mm cable.

For example, could I just put a 32A MCB at the head end and redo the cable calculation based upon that? I do like that idea as it would mean 4mm cable for the first section.

I understand the issues with Part P - I have already done a consumer unit change with new kitchen and bathroom circuits for which I successfully got a completion notice from the LABC.

Thanks for reading this long post.

Regards,

Steve

 

[Pensdown]

Hi

I know there are a lot of threads on these subjects, but I have some rather specific questions that I would appreciate advice on.

A bit of background:-

Our property is built on a hill. About half way down the garden there is a retaining wall 1.8M in height. There is a summerhouse at the bottom of the garden, and a garage about half way between and offset to the side.

Presently, the garage has no electricity supply and the summerhouse was fed by a length of unprotected 4mm T&E which I have subsequently removed.

Future plans include the installation of a hot tub in the lower level of the garden.

Here's a sketch...

Untitled

• slup
• 8 Aug 2008
• 1

What I am proposing to do is run SWA from the consumer unit at the front of the house as far as the retaining wall. At that location, I would ideally like to install some kind of enclosure containing:-

1) MCB for Summerhouse submain
2) MCB for Garage submain
3) RCBO for hot tub
4) RCBO for garden lighting

My two questions are:-

1) Can you recommend a suitable enclosure, or is my idea flawed
2) Would you mind assisting with the cable sizing?

Your idea is not flawed but IMO you're making it hard work for yourself.

The simplist and most cost effective way would be to run a 10mm 3core SWA sub-main into the garage and fit an 8way consumer unit. They are much cheaper than externally rated enclosures.

If you're only having 1no light and 1no socket in the SH you could install a 32amp radial in 6mm 3core SWA from the garage CU and install a fused spur for the lighting.

You could also install a 4way CU in the SH (still fed in 6mm SWA) and wire out to a 32amp ring, 1 lighting, 1 garden lighting and pond pump.

I would feed the hot tub from the garage CU via the same cable route to the SH in 4mm 3core SWA.

You could use an RCD in the garge for all circuits or RCBO's, whatever you prefer

That's one way of doing it but I hope you get others

 

[slup]

Many thanks.

The reason I chose the rather odd route of not putting a CU in the garage is because there is a block paved driveway between the house and the garage that I didn't fancy messing with.

Also, the garage is lower than the house - the garage base is probably 1.5M lower than the DPC on the house because the whole plot is on a slope.

I would somehow need to excavate down at an angle and get under the paving.

If I go down the side of the house, the whole of the first part of the SWA can be surface cleated to the house and the solid retaining wall. The only bits I will then need to bury are the feeds to the summerhouse and the garage.

Steve

 

[dannyboi2003]

Could you not use one of these at your distribution point...

http://www.pudseydiamond.com/products/feeder_pillars.html

You see many local authoritys using them as feeder pillars for street lighting etc. I have no idea how much they cost but you could maybe contact your local council to see if they have any decent used ones available to purchase. Once installed you can house all your distrubution gear inside nice and dry.

All the best
Dan

 

[Steve]

Garage aint far from the house - could you go overhead?

 

[Pensdown]

I was thinking you could follow the same route as your drawing. From the CU to the wall then across the to the garage.

The feed to the SH could either follow the other boundary or run back across the garden in the same trench and down as shown.

In electrical terms the runs are quite short which ever way you go.

Gewiss do a range of external distribution boards

http://www.gewiss.com/

Look under energy products. 40 CDK - Modular watertight enclosures and distribution boards - IP65

 

[slup]

Garage aint far from the house - could you go overhead?

Yes, it's only 2M and about 0.8M of that is taken up with a wall, the rest is a gate.

It would be trivial to construct something which ran across the gate.

I could run the cable through the loft and down the side of the house instead. I wish I had considered this before as I should have made the run inside the house in T&E. The house is now fully decorated inside so no way of getting a cable to the loft now.

I'll redo my drawing a bit later and recalculate the lengths.