Does 1mm SWA exist?

[1Justin]

I was on a domestic site the other day in the pitch dark, surveying for a customer who has a skinny 4 core SWA laid to their shed already and now wants a 13A socket. It was not possible to make out the cable embossed markings since they were underground, but my vernier caliper on a single strand (7 strands per core) made it much closer to 1mm^2 (0.426mm dia) than 1.5mm^2. (0.522mm) (The difference per strand being is only < 0.01mm).

So..1mm SWA. I can't find anyone listing it, - does it exist?

If not, I might assume this is 1.5mm and -it was my semi-frozen calipers which were the problem.

 

[LeeH]

Fail. I know that.

 

[FatAlan]

Thought it was Cross Sectional Area which should be a constant as per calculations. If that is the case I would have thought 1mm square CSA conductor would have a diameter slightly wider than 1mm.

 

[1Justin]

Thought it was Cross Sectional Area which should be a constant as per calculations. If that is the case I would have thought 1mm square CSA conductor would have a diameter slightly wider than 1mm.

Alan. I can see you are having some problems, so perhaps people are not being clear, but it's VERY important you understand it, so here you are:
1MM^2 cross sectional area.
Now for a solid 1mm conductor, 1 = Pi *r^2. -So what is r?
r = sqrt (1/Pi) = 0.564mm, hence D = 1.13mm .
In this example, there would be seven stranded conductors in each core (we are talking SWA which doesn't have solid cores), making up the 1mm^2.
Hence 1/7 = Pi *r^2 and r = sqrt(1/(7*Pi)) = 0.213mm.
Making the diameter to measure with your vernier/micrometer = 0.426mm per strand.
It turns out hat 1mm SWA doesn't seem to exist.. so 1.5mm SWA has a single strand 0.522mm diameter.

 

[FatAlan]

Thanks 1Justin. You've answered my question above by showing the calculation for a 1mm CSA cable and it's diameter being slightly over 1mm. All I was interested in re the OP's original post was the fact that it was mentioned that the diameter of the conductors were actually being measured.

 

[Marvo]

Measuring CSA of wire, especially stranded is always tricky and highly prone to inaccuracy even with a vernier. Rather firstly establish that the conductors are copper then take a known length (longer the better) and measure the resistance, then compare the ohms/meter with one of the charts published by respectable cable manufacturers.

I've worked in a lot of countries and I've never seen SWA manufactured in 1mm. 1.5 mm is the smallest.