SWA to my Garage

[biggerrich]

Hi All,

Looking to run in a SWA to my garage whilst the driveway is up. Run is 20m tops (including up and down the wall bits) and will be buried most of the way apart from a few feet of cleats. I am looking to get a "Garage" consumer unit fitted eventually with a 40A RCD and a 32A and 6A MCB. All I am really looking to use it for is a garage light and two double sockets for the chest freezer/radio and jigsaw/circular saw etc when needed.

Thought I would ask here before I get conflicting info from any Sparks I contact about 2nd fixing both ends.

What size SWA would you suggest me pulling in? Would it be 2 core? Should I pull in an earth cable while I am at it and what size? Can the house end of this be wired into an existing spare MCB? What size MCB would be needed as I have a board that has got a selection of unused breakers.


Thanks in advance!

 

[securespark]

Does your design current really warrant a 32A power circuit?

What is the next size up breaker that discriminates with a 32A MCB?

 

[biggerrich]

Does your design current really warrant a 32A power circuit?

What is the next size up breaker that discriminates with a 32A MCB?

Not sure I understand, just "googled" garage power and have seen most consumer units are a 32 and a 6. I doubt I would need a lot for power as mentioned all I really need it for is the chest freezer and occasional power tools.

 

[Electrifying]

Hi All,

Looking to run in a SWA to my garage whilst the driveway is up. Run is 20m tops (including up and down the wall bits) and will be buried most of the way apart from a few feet of cleats. I am looking to get a "Garage" consumer unit fitted eventually with a 40A RCD and a 32A and 6A MCB. All I am really looking to use it for is a garage light and two double sockets for the chest freezer/radio and jigsaw/circular saw etc when needed.

Thought I would ask here before I get conflicting info from any Sparks I contact about 2nd fixing both ends.

What size SWA would you suggest me pulling in? Would it be 2 core? Should I pull in an earth cable while I am at it and what size? Can the house end of this be wired into an existing spare MCB? What size MCB would be needed as I have a board that has got a selection of unused breakers.


Thanks in advance!

Do you really believe that you won't get 'conflicting' info on this forum??

That's like us believing that you're not doing this job yourself!

 

[biggerrich]

That's like us believing that you're not doing this job yourself! [/quote]


Ha ha, no I have a friend who is a qualified spark (i think) but doesnt do it for a living. Just want to be sure I am asking the right things and not get my leg lifted.

 

[Electrifying]

OK, Rough Guide - If you're gonna do it, you might as well do it right.

You need to calculate the maximum demand in the garage.

You need to determine the supply earthing system.

You need to determine if there are any 'Extraneous Conductive Parts' in the garage.

These three things are important in determining the correct size cable to use.

You will then calculate the cable size and protective device rating that is required for your SWA submain.

You will then need to confirm that the voltdrop is within limits - remember, this is calculated from the origin to the last light in the shed.......and with it being 'lighting' is only 3%.

If it complies, you now have your MCB size and your cable size, if not, you'll probably have to go up one in cable size.

Still want to do this??

 

[biggerrich]

Theres me thinking it would be a good idea to pull the cable in myself while doing the drive. Will ask my mate, see if a crate of beer softens the blow.

I assume the cable will have to be buried a certain depth? Is that under your working codes or just building regs? Does it matter that it is currently a concrete drive and will be mono block in the very near future.

 

[holmslaw]

..

 

[biggerrich]

Thanks for the pdf. Spoke to my mate who said 4mm 3 core. Digging the drive up in the next couple of weeks so will do it then.

Would I need to marker tape the duct (if used)?

 

[EFLImpudence]

Why would you not?

 

[Electrifying]

Thanks for the pdf. Spoke to my mate who said 4mm 3 core. Digging the drive up in the next couple of weeks so will do it then.

You need to calculate the maximum demand in the garage.

You need to determine the supply earthing system.

You need to determine if there are any 'Extraneous Conductive Parts' in the garage.

Did your mate take these three things into account - or did he just say "4mm, 3-core will do"...........just wondered if your taking notice of any advice on here?

 

[Beelzebub666]

I did something similar, though the electrician was a little more demanding than yours it seems. He specified the cable, which was 3 core, and inspected how I laid it before it was buried. It runs to a switch fuse rather than an MCB in the house.

 

[securespark]

Thanks for the pdf. Spoke to my mate who said 4mm 3 core. Digging the drive up in the next couple of weeks so will do it then.

You need to calculate the maximum demand in the garage.

You need to determine the supply earthing system.

You need to determine if there are any 'Extraneous Conductive Parts' in the garage.

Did your mate take these three things into account - or did he just say "4mm, 3-core will do"...........just wondered if your taking notice of any advice on here?

Just re-read this.

4mm2 SWA installed as you describe may not be suitable for a 40A breaker. I'm not even sure if 40 & 32A MCB's discriminate.

You sure he knows his stuff?

 

[EFLImpudence]

4mm2 SWA installed as you describe may not be suitable for a 40A breaker.

It isn't - In ducting or just buried 2 core is rated at 37A , 3 core only 30A.

(But are you thinking of the 40A RCD quoted)

Anyway, more designing needed.

 

[bernardgreen]

At this stage lay in two 32mm internal diameter ducts in the trench and allow youreself a lot of freedom as to what size SWA is installed after a full design has been carried out. One duct for the power SWA and the other for other cables.

Use a vacuum cleaner to suck draw strings through the ducts.