powering a detached garage

[dazza74]

Hi, Looking for a bit of advice. Have a currently detached garage, fed from the house under RCD on 2.5mm SWA, to a 2 way CUSU in the garage powering one socket ander one Light on a 16a and 5a breaker in the garage. I want to fit more sockets in the garage and think of future power needs. Im planning on running a new 4 or 6mm SWA to the garage but can't bury it like the existing one. ( water mains too close and drainage all under tarmac) So was going to cleat it to the house and conservatory for about 15m then bury it only approx 4ft under a path which is soil. does that sound acceptable. (not ideal about having it round the house buy way too expensive to dig and risky) I can only get about 12-18in down under the path due to hitting hard ground. the other way is to run the SWA in the cavity to the roof, (I have a draw wire already) across the house and back out down an external wall. thenot straight under ground for a couple of meters. any advice is appreciated

 

[LankyWill]

Don't forget your bonding if your supply is PME, minimum 10mm earth.

 

[Rpa07]

What are your intentions for power usage in said garage - have you calculated the load? Good first step as 2.5mm already in will see you on the usual suspects and making your lighting more energy efficient might save you a lot of bother.

 

[dazza74]

Hi, it is a PME system. If I take from the existing house CUSU from a 40a breaker on the RCD side woukd I still need the 10mm. there's an existing 2.5mm SWA already installed for the garage back when the house was built 15 years ago. but I can see more power being needed in the future.

 

[telectrix]

if you have extraneous metal parts, e.g. water, in the garage you'll need 10mm bonding cable as it's pme. easiest way is to use 10mm 3 core SWA. and clleated to the hose brickwork is acceptable.

 

[dazza74]

Hi. I will be converting the garage into 2 rooms a work room so ideally would 2 sockets and a light. and a store room, 1 socket for freezer and a light. I'm currently using the 2.5mm cable to run a freezer in the garage and a few odd bits now and then. as we need building regs for the conversion I was just after doing this bit right before any building work starts. ideally as cheap as possible but correct

 

[Octopus]

If you are involving building regs they may well be looking for certification of the electrical works .... How would you plan to deal with this?

 

[Ian1981]

If you have extraneous conductive parts in garage you can always TT that end if you don't want the expense of buying bigger 10mm swa and bond the extraneous part to the garage consumer unit.

Also worth noting that guidance note 8 advises that when using a core in a swa for combined cpc/bonding conductor that diverting neutral currents in pme systems can cause the conductor to heat up and possibly derate the ccc of the live conductors.
Think that's more the case with bigger sized installations tho rather than domestic.

 

[dazza74]

thanks for that Ian. i didnt know that. il ot planning on ever drawing too much current to probably cause that. but good to know.