SWA for man cave

[G and J]

At the bottom of my garden there is a man cave and playing with the online voltage drop calculators it seems I would be ok with 6mm but I may go for 10mm to be sure.  
 

What I can’t work out is if I need a two or three core cable.  I’m finding it confusing as they don’t seem to have insulation colours that I would expect.  
 

What do I need?

[andyscotland]

Historically, in most cases people used 2-core SWA for single phase circuits, using the outer steel armour as the CPC (earth). This is often ok in principle although it does need to be checked/calculated as the resistance of the steel isn't always appropriate for the circuit.

 

Many people (including me) these days prefer to use a copper core for the CPC even if we could theoretically use the armour. The resistance is better from day 1, less to check, and armour and its terminations often corrodes & degrades over time. The sheath still needs to be earthed at at least one end to protect the cable, but is not officially part of the circuit.

 

3-core SWA was traditionally used for balanced 3-phase loads e.g. motors, as these do not have a neutral. This is why the cores are coloured for the three live phases (brown, black, grey).

 

You can use that cable for a single phase circuit if you sleeve the cores at both ends. However there are manufacturers now making it in the correct colours (brown,blue,green&yellow) and it would be better practice to use this - it's fairly easy to source.

 

This all assumes that it is ok to export the supply earth to your outbuilding. That depends on a number of factors including distance, type of construction of the building, whether any other services are present etc. It may not be safe to use the house earth - if not then you would use a 2-core cable with the armour earthed at one end and then fit an earth spike.

 

Bear in mind for cable sizing,  voltage drop needs to be considered to the furthest point of your circuits (e.g. including the wiring within the man cave) and you also need to consider the Earth Fault Loop Impedance for the circuits to suit the type(s) of protective devices.

 

I'd almost always go up a size for something like this: the extra cost is marginal and it buys you a lot of future-proofing. You only want the hassle of running the cable once.

 

To be honest as you can maybe see there are a few site-specific things that need to be checked/calculated to do this safely.

 

Terminating SWA properly also takes a bit of skill/experience.

 

This is therefore quite an involved job to attempt without an electrician to advise - it's beyond the normal realm of DIY (and I think notifiable in England & Wales? Not sure as I'm in Scotland and our rules are different).

 

If you are keen to do it yourself then you'll probably want to do more research on some of the things mentioned above, and you'll definitely want to buy extra cable to have a practice before you attempt to terminate the real thing.

[G and J]

Thank you Andy. That’s helped enormously.  

[Onoff]

You might also consider running your SWA in oversize ducting. You can then run Cat-5/6 cables etc in smaller ducting within.

[Onoff]

Well worth a a watch:

 

 

[Adrian Walker]

Or use Doncaster EV Ultra that has CAT5e inside https://www.yesss.co.uk/ev-ultra-cat5e-cable-4mm2-3-core-data-pvc-steel-wire-armour-black-0  

They do a 6mm2 and a 10mm2 version.

Edited Thursday at 19:22 by Adrian Walker
added some stuff

[Onoff]

Just run separate SWA and Cat-6e to your EV charger like I am:

 

 

[G and J]

Thank for all this guys.  
 

It’s a long run (over 40m) so the Doncaster cable option works out rather more expensive so I’ll go separate.  Neat idea for my EV point at the front which is a very short run.  
 

I've ducting going in that can take the Ethernet cable anyway, and I like the idea of keeping it away from the mains cable.  

I’ve found a source of single phase coloured cable - however my sparky is back earlier than expected and tells me to use 3phase coloured cable to save money.  I’ll do what I’m told for once. 

 

[Onoff]

Mine in the picture above is old colours, red, yellow,blue,black 10mm². Red sleeved with brown, blue as is, yellow sleeved with green/yellow and black left spare. 

 

I'm coming in through the back of the EV charger as coming up into the bottom is just plain fugly imho.

[ToughButterCup]

On 26/11/2025 at 08:22, andyscotland said:

...

Terminating SWA properly also takes a bit of skill/experience.

...

 

Now you tell me.

Could have done with that advice before I tried to mend the SWA cable I pulled up (and snapped) with the digger.

Mind you if I'd taken all the advice so generously offered on this site  I'd have finished our build long ago.

 

Instead I break stuff and then - when furious with myself for being so stoopid - I read the instructions.

 

Our electrician came out and mended the SWA for me one freezing  Bank Holiday evening 20 minutes after I'd rung him.   James at  CEPS 

[Nickfromwales]

On 27/11/2025 at 19:21, Adrian Walker said:

Or use Doncaster EV Ultra that has CAT5e inside https://www.yesss.co.uk/ev-ultra-cat5e-cable-4mm2-3-core-data-pvc-steel-wire-armour-black-0  

They do a 6mm2 and a 10mm2 version.

🫡

On 27/11/2025 at 21:36, Onoff said:

Just run separate SWA and Cat-6e to your EV charger like I am:

 

 

If it’s to the EV then is the intention for the EV charger to have internet connectivity or for the cat cable to get you a set of CT clamps back at the head / meter?

 

Doing this for a current client atm, but was thinking to run a second (separate, duct-grade) CAT6 to the carport to offer up a future WAP there. Cables cheap enough to put a redundant run in (<35m).

 

So the hybrid cable @Adrian Walker linked to, is that cat cable intended for CT clamps? Only now dipping my toes in the EV charger waters…..

[G and J]

6 hours ago, ToughButterCup said:

 

Now you tell me.

Could have done with that advice before I tried to mend the SWA cable I pulled up (and snapped) with the digger.

Mind you if I'd taken all the advice so generously offered on this site  I'd have finished our build long ago.

 

Instead I break stuff and then - when furious with myself for being so stoopid - I read the instructions.

 

Our electrician came out and mended the SWA for me one freezing  Bank Holiday evening 20 minutes after I'd rung him.   James at  CEPS 

“Experience is something you don't get until just after you need it.”

You too huh?  Depressing, isn’t it.

[Temp]

I'm a bit late but I found this useful...

 

https://electrical.theiet.org/media/1695/electrical-installations-outdoors-a-supply-to-a-detached-outbuilding.pdf

 

[andyscotland]

That's a helpful overview @Temp, worth noting that it is based on quite an outdated version of BS7671 - much of the content is still appropriate but for example the information about RCD protection is not entirely accurate these days (though the end result would likely be the same, other than perhaps for the "spur on a ring main" scenario they describe).

[Adrian Walker]

3 hours ago, Nickfromwales said:

 

 

So the hybrid cable @Adrian Walker linked to, is that cat cable intended for CT clamps? Only now dipping my toes in the EV charger waters…..

 

The Doncaster EV-Ultra cable contains four twisted pairs, more than enough for clamps and data

[-rick-]

23 minutes ago, Adrian Walker said:

The Doncaster EV-Ultra cable contains four twisted pairs, more than enough for clamps and data

 

1 gigabit ethernet requires 4 pairs with specific properties. Most people installing data will these days will want to install something that supports faster speeds*. For faster speeds the spec of the cable really matters. Cat6A spec is what you should be aiming for and can support 10 gigabit ethernet (and HDBase-T for HDMI, etc). Cat5 spec might handle that over short distances (35m max) but that's it. Routing an ethernet cable directly parallel and closely coupled to a mains cable is generally frowned on.

 

I'd guess the main question is whether this 'cat5' cable with in the EV Ultra cable actually meets the spec for Cat 5. Firstly, there are multiple 'EV-Ultra' cables, some with only 2-cores of data, some offer 2xcat5e spec (2x4-core). Looking at the datasheets, I'd guess that the 4-core cat5e FTP cable version does meet the spec for gigabit ethernet. You can probably run 2.5g and 5g on it as well. 10g likely very limited. As it's a shielded cable (FTP) that does give some reassurance about interference from the closely coupled mains cable.

 

* 1gig ethernet is approximately 100MB/s. With the storage on modern computers being capable of >3000MB/s, 1 gig ethernet can feel very slow if trying to access a NAS or similar though it's fine if all you want is internet access.

Edited 2 hours ago by -rick-

[Adrian Walker]

53 minutes ago, -rick- said:

 

1 gigabit ethernet requires 4 pairs with specific properties. Most people installing data will these days will want to install something that supports faster speeds*. For faster speeds the spec of the cable really matters. Cat6A spec is what you should be aiming for and can support 10 gigabit ethernet (and HDBase-T for HDMI, etc). Cat5 spec might handle that over short distances (35m max) but that's it. Routing an ethernet cable directly parallel and closely coupled to a mains cable is generally frowned on.

 

 

Agree with your comments. This cable, as the name suggests, is for an EV charger of less than 20 metres, for voltage drop reasons. It was designed so that an EV charger only needs one entry point for data and power.

[Onoff]

1 hour ago, -rick- said:

As it's a shielded cable (FTP) that does give some reassurance about interference from the closely coupled mains cable.