Is it worth adding additional cores when buying SWA?

[d000hg]

I’m planning a 30m SWA cable run to a detached outbuilding. I’ve calculated 4mm2 cores are sufficient (2.5% voltage drop at 4kW so I can run a small heater).
A small consumer unit will be installed probably 2 circuits (lighting and one or two sockets).

I already have a conduit buried and don’t want to pull the cable more than once I like the idea of redundancy but am not sure if it achieves anything… realistically how many cores?

 

[pcaouolte]

What is going to happen to it to cause you to need the extra cores? It will survive happily in the conduit for more years than you will need it.

 

[d000hg]

What is going to happen to it to cause you to need the extra cores? It will survive happily in the conduit for more years than you will need it.

I’m more thinking would there be any scenario where having more is useful, than damage. I’m not going to switch to 3 phase But is there any other common case I might need an extra wire?

I might add Ethernet but that’s totally separate. All I could think of was a control wire but for what!?

 

[Murdochcat]

If you have ducting in place then having spare cores is largely a waste of money as a replacement cable could be pulled through

 

[AndyPRK]

4 core is sensible if you wanted to remotly switch an external light.

 

[d000hg]

For a run of 30m would I need a separate bonded Earth at the outbuilding out of interest?
Not a job for me but I like to know, and I can’t find the rules for this

 

[AndyPRK]

Probably.

What’s your supply earth type

 

[d000hg]

Probably.

What’s your supply earth type

I am not sure I even understand the question properly we have an old dedicated overhead cable running 100m up our drive from the road (just to our house) and a brand new meter/supply was fit ~3 years ago off the pole (they replaced the cable to the meter and everything). We have the main consumer unit coming off that which has an earth rod sunk into the ground on the exterior wall of the building (so it is accessible).

 

[robinbanks]

I might add Ethernet

Tape it to the SWA when you pull it

All I could think of

If your needs (loads) change in future you have spare current carrying capacity?


Personally I wish I'd run cat6 to every light switch and socket in my house when I built it. Only woulda taken a day but the number of times since I have wanted some control for smart home auto / networking in an awkward spot...

 

[sparkwright]

If you don't fit a cable with spare cores (or larger CSA), consider pulling in a draw rope with the cable for future use.

 

[JohnW2]

If you don't fit a cable with spare cores (or larger CSA), consider pulling in a draw rope with the cable for future use.

It's a fine theory but whenever I've tried that the pull string/rope has become twisted around the cable being pulled through with it, with the result that it became useless for subsequently pulling other cables through.

Am I the only person who has experienced that problem?

Kind Regards, John

 

[SUNRAY]

It's a fine theory but whenever I've tried that the pull string/rope has become twisted around the cable being pulled through with it, with the result that it became useless for subsequently pulling other cables through.

Am I the only person who has experienced that problem?

Kind Regards, John

You are not alone...
there are ways to reduce the problem, plaited cord rather than twisted rope for a start

 

[JohnW2]

You are not alone... there are ways to reduce the problem, plaited cord rather than twisted rope for a start

I'm not sure that the type of 'rope' would make all that much difference. The problem is that if the cable+rope rotate by much more than 180° whilst being pulled in together (something which seems almost inevitable with 'simple pulling') one is effectively sunk! To avoid thee problem requires prevention of axial rotation of the cable+rope pair during pulling, and I think that's easier said than done!

 

[Murdochcat]

It's a fine theory but whenever I've tried that the pull string/rope has become twisted around the cable being pulled through with it, with the result that it became useless for subsequently pulling other cables through.

Am I the only person who has experienced that problem?

Kind Regards, John

Was the ducting big enough?
Tight corners on the ducting
was the draw cord made of?

Never struggled with this myself

 

[robinbanks]

I've not had a problem either, but it does help to keep them separated on the input. It's also possible to blow or suck draw cords through after, starting with a light weight one that you use to pull a heavier cord through, driven by a blockage such as a carrier bag. Depending. The size of the duct you may get away with even a domestic hoover or compressor