External Wiring

[PaulH]

I have just moved to a new house and it has a workshop (shed) in the garden.

The total plot size is 9m X 18m, whith the (detached) house at the front and the shed at the back right hand corner. The garage is on the front left hand side, and the consumer unit is on the outside wall. On the left hand side of the house is a grass verge and then a road. - All this info becomes relevant!!!

Currently the power to the shed was provided by a spur off the ring main. This provided power for 6 double sockets and a light!!!

Obviously I need to rectify this dangerous situation.

I want to install a new MCB in the consumer unit and have this protected by the RCD. There are currently 2 32A MCB (Upstairs and Downstairs) proteced by the 63A RCD. Do I need to upgrade this to a 100A RCD? Also, instead of putting in an MCB for the new circuit, can I put in an RCD? (So in effect, this circuit is protected by the main RCD and also by its own RCD).

Am I allowed to run the new cable along the outside of my garage to the garden? This means it will run "along" the grass verge.

Does this setup exceed the 100m2 area rule? i.e. do you calculate this area by imagining a square with the consumer unit in one corner and the shed in the other and then working out the area of the square?

Thanks in advance for your help.

Paul

 

[paulfromswindon]

Hi,

A bit complex, but here you go:

I'm assuming that you have a split consumer unit with half of it protected by the RCD? Also, I am assuming it's an RCD with 30mA trip rating? If It's 100mA you will need to fit a 30mA for the shed (the wording suggests it will be 3omA). 63A will be fine unless you are using a lot of equipment.

First, please understand an RCD does something different that an MCB, so you must have an MCB and RCD protecting this ciruit.

I would wire the shed in SWA (Steel-wire-armoured) cable, from it's own MCB, then put a small consumer unit in the shed, feeding a circuit for the sockets and lights.

Be aware that the armour of SWA must be earthed correctly.

The SWA can be clipped along the outside of buildings, but not laid on the ground - it must be buried at least 18 inches if this is the case.

If the shed is more that 10m from the house or garage, or your supply is PME (it should say on a yellow sticker by the meter), you may need to use an independant earth at the shed (there is another thread about powering an outbuilding). Also, the lenght, as well as the loading, will dictate what size cable you need to use for the sub-main.

I assume that the 100m2 rule you are referring to is the one that applies to Ring Circuits - it's not relevant for a submain.

A final word of advice - powering anything outside the house poses additional risks - if you are not sure, please consider using a professional sparks, even if just for wiring the sub-main to the shed.

Cheers

Paul

 

[Scoby_Beasley]

Just a query Paul, are you still allowed to run overhead lectrics to outbuildings (obviously supported by cables)? I know you could do it years ago.
P.S. Hope you got sunburned

 

[paulfromswindon]

yep, overheads are OK as long as they are well supported and the right type of cable (ie not vulnerable to moisture, for instance SWA). And obviously as long as they are high enough!!

I didn't get sunburned. Hardly even tanned. Not for want of trying. Hey-ho!!

 

[Scoby_Beasley]

Is 8' high enough?

 

[paulfromswindon]

As long as your not 9' 6"!!!

Yep, that sounds about right..

 

[Nick3]

here is some info about running cable overhead

through steel conduit height 10ft min span 10ft max

on catenary wire height 12ft min span unlimeted

un suported height 12ft min span 10ft max

 

[masona]

As long as your not 9' 6"!!!

I think he's 9' 6" at arm lenght when lying down,hic