How to establish the CSA of multi-strand SWA.

[Win9R]

Hi

I'm new here and hope that someone can advise on a project I am currently working on.

I intend to supply power to a garden building directly from a spare MCB in the consumer unit in the house, which equates to a total distance of approximately 30m, although the route that the cabling is going to have to take to reach the CU is far from straightforward.

I have a couple of questions that I'd appreciate thoughts on, please:

1. I've acquired approximately 20m of SWA but it has no markings on to denote what CSA it is. I was intending to use 6mm but I'd like to be sure about the size of this cable before actually using it. The SWA has 7 strands per core and I know the diameter of both the collective and individual strands, from which I can calculate the CSA of each, but I'd appreciate if someone could confirm the correct way of establishing exactly what size this cable is because using the collective diameter gives a very different result to using the diameter of a single strand and multiplying it by the number of strands. Using the method that I believe to be correct (single strand multiplication) suggests that this cable is only around 2.5mm but when I use the old-fashioned method of physically comparing the size against another cable with a known CSA it appears to be close to 6mm. Confused!

2. As I mentioned, I currently do not have sufficient SWA for the entire route to the CU (yes, I could buy some more) and for this reason and the fact that the route for the cable to take to get from the garden building to the CU in the house is less than straightforward I was wondering if there would be any reason why I could/should not run SWA through the garden (buried and installed under paved areas) and convert it in a junction box to non-armoured single cores on the external wall of the house, from where this would run through conduit to the CU? The non-armoured single cores would be the same size as the SWA, assuming that I can establish what size that is with any degree of confidence!

I should mention that all connections will be performed by a qualified electrician and that the above queries are intended only to help me try to with my decision making.

Many thanks in advance for any thoughts or advice that anyone may have to offer.

Paul

 

[Pete999]

Just work out the loading, voltage drop, installation method,size of OCPD required, ascertain what sort of supply you have in your property, type of earthing etc, will there be any other services in the building you intend to supply eg gas, water.

 

[telectrix]

as above. also, you could compare with some 6mm cable at your local wholesaler, but the best thing is to get your electrician invlolved first. he will then advise on cable size and more than likely allow you to do the groundwork, and perhaps lay the SWA ( don't fill it in though till he's inspected and tested it\). good luck.

 

[YoungBart]

Most cable manufacturers such as Doncaster Cables or Draka have some sort of chart on the web which tells you the overall diameter of cables, This could possibly be used to give a rough guide. However as has been stated above, have a chat with your electrician and he will ensure you are installing the correct cable for the requirements.

 

[HandySparks]

What's the diameter of each strand?
What instrument did you use to measure it?
What to you calculate the csa of the cable to be?

 

[Adie moore]

For the sake of 60 odd quid you could get the job done easier and probably quicker. By the time you have bought cinduit and stuff too. And does it need to be 6mm?

 

[HandySparks]

And does it need to be 6mm?

I guess it depends on the load the OP designs the circuit for. At 30m, the sizing will probably depend on volt drop.

 

[Adie moore]

I guess it depends on the load the OP designs the circuit for. At 30m, the sizing will probably depend on volt drop.

Absolutely, but all the op says it's feeding is a garden building. So anything from a flori and a socket up to a hot tub.

 

[HappyHippyDad]

The OSG has the resistance values for all different sized conductors. If you have an accurate meter you could measure the end to end resistance of one of the conductors, that should give you an indication of what size cable it is. If you have a 6mm cable to hand as stated you really should be able to visually see if it is the same. Sometimes it is difficult to distinquish between 6mm and 4mm, but if you are thinking it may be 2.5mm there should be a noticable difference.

As handy has said, how did you determine the CSA of each strand? I think I would have measured each strand with a set of calipers or micrometer and taken the average if I HAD to do it this way.

If in doubt about the CSA of the cable I'd be buying some more for the sake of 20M, although I expect the electrician will be able to work it out.

 

[amlu]

i have a box of insulated bootlace ferrules, from 0.25mm to 6mm csa. put them over the cable see which one fits.

 

[Octopus]

I should mention that all connections will be performed by a qualified electrician and that the above queries are intended only to help me try to with my decision making.

Many thanks in advance for any thoughts or advice that anyone may have to offer.

Paul

Ask your sparky. I wouldn't be considering testing and signing off a supply as you describe without any consultation before its done.....

 

[ferg]

Ask your sparky, he'll look at the cable and tell you what it is.

Same for jointing the cable within the building.

Any joint introduces a potential point of failure and is, where practicable, avoided.

This sounds eerily similar to a job I'm going to do for a wet head friend of mine.

Clearly you are not one and the same as you can write coherently and therefore cannot possibly be a plumber.

 

[ruston]

Just say what you think there Ferg. Don't be shy.
Nice to see you again.:flowers:

 

[ferg]

You know me always beating round the bush.

 

[ruston]

You know me always beating round the bush.

Sounds like fun.:biggrin:

 

[ferg]

Sounds like fun.:biggrin:

Dirty old sod.

 

[ruston]

Dirty old sod.

You started it.:wacko: