Garage Supply

[barch]

Hi All

I'm updating my supply to the Garage. Currently there is a length of flex running between the house and garage about 8 foot in the air, not protected at all which plugs into a socket in the loft which is on the upstairs ringcircuit.

I'm going to put in a garage board with an RCD and I'll run a 6mm cable from the cu to junction box where I'll then connect 4mm SWA cable. ( The reason I've chosen these sizes is because screwfix supply them, can t see matching sizes!) The SWA cable will run down the side of the house in metal conduit into the ground and appear in the garage. I know the regs state that the SWA cable needs to be 450mm underground but my drain runs between the garage and the house and is less than 450mm deep. Do I have to route the cable right aroind the garden just so its 450mm deep or are there exceptions?

thanks

 

[jj4091]

Do you mean the drain crosses the path of the cable? How deep is less than 450mm?

 

[barch]

The drain, and its the toilet waste (which I had to unblock this weekend) is only about 12" from the surface.

 

[jj4091]

You don't need conduit for swa down the side of the house, sorry but I still do not understand properly what the problem with the drains is. Are they following the same path as your preferred cable route?

 

[barch]

The garage and house are about 8-9 feet apart. So between the two points of entry in the garage and house is a pathway. The main waste passes along this path, coming from around the back of the house, turning down past the side of the house and garage. So, the drain runs parallel with the house and garage

clearer? I hope!!
cheers

 

[Taylortwocities]

So, if your SWA has to cross the drain, your dig the trench ( >450mm if its under lawn or flowerbeds) up to the drain and on past the otherside, run the SWA under the drain.

If your SWA route is going to be under concrete/paving slabs then it doesnt need to be so deep.

 

[barch]

Aaaah, Yep, its going to be completely covered by concrete. What depth has it to be then?

thanks

 

[Taylortwocities]

The Reg (522-06-03) only says 'sufficient depth to avoid damage by any reasonably foreseeable disturbance of the ground'

400mm is a guide for cable buried in lawn & flower beds (approx 2 spade depths, I believe).

Wherever it is you need to put in cable, a layer of soil, warning tape to show there is cable underneath and then fill in the rest.
If its under concrete/slabs I would suggest a foot is OK.

Theres a good article on what you have to consider at http://www.iee.org/Publish/WireRegs...matters_electrical_installations_outdoors.pdf

 

[barch]

Very interesting. thanks

 

[ColJack]

nobody's asked what kind of loading do you intend to have in the garage?

4mm² SWA is good for 38A at a push.. ( how do YOU read these tables? i figured ref method 1, clipped direct and 1 two core cable single phase a.c.... however it's a 3 core cable but not 3 phase as per column 3.. )

the nearest breaker is 32A..

6mm² swa is readily available from all good electrical stockists and there's bound to be one in your area somewhere.. they'll be cheaper than screwfix normally too...

and fancy screwfix not selling 4mm² T+E.. how do you do 32A radials without it?

 

[plugwash]

4mm² SWA is good for 38A at a push.. ( how do YOU read these tables? i figured ref method 1, clipped direct and 1 two core cable single phase a.c.... however it's a 3 core cable but not 3 phase as per column 3.. )

I'd say treat it as a 2 core cable since the third core does not carry current under normal conditions.

 

[davelx]

I'd say treat it as a 2 core cable since the third core does not carry current under normal conditions.

As does note 3 to table 6E1 in the OSG