Cross section of cable.

[soup]

Does anyone have a favourite site, to work out the CSA required for a piece of cable, basically I want to make up an extension to run a circular saw (1200 W) [at 240V that is 5A] asked the chap in the local Hardware shop for cable large enough to deal with 2 kilowatt (mmm over speccing as usual), he said he had nothing that could deal with that much power 2k was "cooker sized", but my kettle (e.g.) is 2200 W, so can't trust him as far as I can throw him.

[Dave]

:-)

Dave

[Smudger]

soup said the following on 27/09/2005 17:25:

The IEE Wiring Regulations (BS7671) provide tables of the current carrying capacity of cables.

For your example, PVC flexible cord for extension cables to BS6500 is covered in table 4H3A:

2kW @ 230V implies a current of 8.7 Amps. You should therefore use as a minimum 1.0 sq mm flex, which has a rating of 10 Amps. You would need to put a 10 Amp fuse in the plug.

However, you should consider using 1.25 sq mm flex which has a rating of

13 Amps and therefore allows you to use a standard 13 Amp fuse in your plug.

Most extension cables rated at 13A you buy in DIY sheds will be made with 1.25 sq mm flex.

If you want to run a largish load at a long distance, you should consider using 1.5 sq mm flex, which will have a lower voltage drop.

You could also look here:

[Soup]

Thanks all, will take a dawnder down to B&Q tommorow to buy 1.25 mm^2 cable, hopefully they will sell it by the metre, may even get 1.5mm^2 depending on price, not too bothered if wire is a bit thicker and less flexible. BTW Seem to remember there is a difference viz wire V cable V flex does anyone know what this difference is.

[Harry Bloomfield]

soup formulated the question :

I would suggest 1.5mm 3 core, not because of its current carrying capacity (it would be much more than adequate), but for its robustness. It would also help keep the voltage drop down to a low value.

[Harry Bloomfield]

Soup pretended :

If the cable is to be fitted with a 13amp socket at the end, then it _must_ be 3 core.

[Harry Bloomfield]

Soup wrote on 27/09/2005 :

If you mean solid core, versus flexible core, then you _must_ use flexible otherwise known as flex.

[Lobster]

They don't sell it by the metre any more. Why not just get a made-up extension cable or cable reel? They will be labelled with the current rating - so never mind about cable thicknesses - eg for at Screwfix, for £4.25 (10A):

capacity you need is really not at all 'special'; it's not as if you're trying to run a 3kW fire or a toaster at the end of a 100m extension or something!

David

[soup]

> The capacity you need is really not at all 'special'; it's not as if

Thing is I have a "plug" and a "trailing socket" which I was going to make up into an extension with cable from a hedge trimmer but noticed in time that the cable from the hedge trimmer was only two core and an earth wire was required as well, so thought I will just nip to the local hard ware and get a piece of cable that started the whole "cooker size" thing, which really confused me, after all I was told 2kW was lots of power and yet lots of the appliances in my house were there or thereabouts. Will need to rethink now I have found out B&Q don't sell cable by the metre . Mmm may well get cable from local shop but without listening to any of the words coming out of his mouth.

[Colin Wilson]

Depending on how much length you want to pick up, IIRC you might also come across a reactive resistivity if you leave the majority of it coiled up. Can lead to the cable warming up, and in extreme cases, melting the insulation.

Its been a while since I played with the stuff in the "real world" though, so my theory is now very patchy :-(

[soup]

Since "doing" resistance,inductance and capacitance at college (a long time ago) have always uncoiled any extension, but as has been pointed out this is hardly at the cutting edge, I was just looking for the size of a bit of cable to "cobble-up" an extension to chuck in a box beside a circular saw .

[Will Dean]

Hmmm.

The reason it gets hot when it's wound up is because it can't cool-down because it's all in a lump. It's nothing to do with inductance. To a first approximation, it would be exactly the same with DC.

The unwound cable is wasting almost exactly the same amount of heat, but it's not getting so hot because it's more spaced out.

Yes. But you're right that you shouldn't use wound-up extension cables except for very light loads.

Will

[Andrew Gabriel]

General guideline for extension leads fused at 13A...

1.25mm² up to 12m long 1.5mm² up to 15m long 2.5mm² up to 25m long (2.5mm² flex won't easily fit in a 13A plug). These come from the PAT testing recommendations, with the earth fault loop impedance being the limiting factor.

Lengths can be increased with a proportional reduction in the value of plug fuse value fitted in the extension lead, e.g. with a 5A fuse fitted,

31m, 39m, and 65m respectively for the three cable sizes above.

[meow2222]

starting with the wrong specs isnt going to help much

NT

[soup]

What wrong specs? Item it is for is 1200W saw but extension may be grabbed to be used for something else hence wanting an earth lead (saw is double insulated) and a power rating of 2kW.