SWA Armoured Cable Thickness

[nickldn]

Hi,

I need to run some SWA cable from a domestic consumer unit to a garage about 10 meters away and am wondering thickness of cable I would need.

The consumer unit in the garage is a 2 way MCB unit and runs a 32A and an 10A output. It will run a couple of sockets and some overhead lighting.

Will 2.5 mm cable be enough, or am I better off with 4 mm?

Thanks very much,

Nick

 

[oharaf]

Being a registered qualified electrician you know that for such purposes you will need to run 10mm triple sheathed SWA with an earth rod due to the high EFLI that is likely to occur on energising the 32A Radial circuit

 

[Adam_151]

WTF, oharaf

 

[sparkyspike]

WTF indeed!???


You need to calculate your cable size mathematically, rather than guessing.

Firstly, is they any metal pipework or exposed structural steel in the garage? (This may be Oharaf's point.)

Secondly, are you running the cable in the ground, or over ground (or on a catenary wire)?

Thirdly, calculate your design current (the max current you will be using) and then use this to calculate your fuse size.

Then select the cable according to the fuse size, installation method and voltage drop. If you work out the first three things, then we can do the rest for you.

You will need to notify this work in order to comply with building regs.

 

[oharaf]

Sorry cannot help being sarcy at times. I just get a little bit tired of hearing the same question time after time, when clearly people don't really know what they are doing.

If they just gave the required details then we could give a pretty comprehensive answer, but it is mainly the fact that ALOT of us have spent time getting qualified and paying the 'registration tax' so we can do such works.

The system is definitely working against us, HIP's being another prime example.

 

[sparkyspike]

I just get a little bit tired of hearing the same question time after time, when clearly people don't really know what they are doing.

Well, stop reading the posts then!

The system is definitely working against us, HIP's being another prime example.

It's working for me. HIPs, Part P, 17th edition - all mean that approved installers are doing more work that used to be DIY.

I've never been so busy!

 

[oharaf]

Glad to hear it, Sparkyspike. You're right. You know what I think I'll do a guide and stick it in the wiki

 

[sparkyspike]

I'll do a guide and stick it in the wiki

You'll get six years for that!

 

[nickldn]

Well I will need to notify it, before I actually get around to doing it.

I'm still in the early planning/costing stages...

The cable will be running in the ground, underneath the patio. There is no adjacent pipework along that section of ground. There's also no exposed metalwork in the garage, it's just a simple brick built structure.

There will be two 13A sockets running off it, I'll not be using an electric double oven in the garage!

I might well decide to get someone qualified to do it after looking at it in more detail, but it's good to know what you're talking about!!

 

[sparkyspike]

I think you'll end up using 4mm 3-core SWA. This should be good enough for both 20A and 32A over the ten metres (plus a bit more for connections!). So you have some scope for which breaker to use. 2.5 will be pushing it on both installation method and voltage drop over that distance.

Better to be prepared to put in a bigger cable - that way you can budget for it. It's a good idea to involve an electrician sooner rather than later, as he will give you your design current and will select the correct cable. But you should still be able to do some/most of this work yourself.

 

[nickldn]

Thank you for that, 4mm cable sounds sensible.

At least now I know roughly what I'm talking about when I speak to a pro!

One more question, would 6mm cable be overkill?

Thanks,

Nick

 

[sparkyspike]

No. It won't be overkill. It will just be more expensive.

But it may give you the possibility of increasing the load at a later date. Also, 6mm will run nearer to your supply voltage than 4mm.