what is my swa core size

[jabmesen]

Hi - I assumed some swa cable was 3 core 2.5mm , but I have done some calulations based on the strands in each core and suspect it to be 4mm - obvs that is great news... also on the outer the cable reads BS5467 BASEC DEMFS KABLO 3 x 4 2010....3x4 means 3 cores of 4mmsq ?

 

[binky]

yep! what are you planning on using the cable for?

 

[jabmesen]

Thanks for getting back to me - really helpful- so the 3x4 inscription means 3 cores of 4mmsq ? Im not planning anything special - just 13amp stuff- there was a 32a mcb on the circuit and I was concerned thats all- but at 4mm that should be fine I think? I wish there was a clearer way of showing the cable sizes- if i could just measure the outside of the swa and know- that'd be great!
btw- I measured 7x 0.83mm diameter strands in each core- I made that 3.7mmsq- sound about right?

 

[binky]

Thanks for getting back to me - really helpful- so the 3x4 inscription means 3 cores of 4mmsq ? Im not planning anything special - just 13amp stuff- there was a 32a mcb on the circuit and I was concerned thats all- but at 4mm that should be fine I think? I wish there was a clearer way of showing the cable sizes- if i could just measure the outside of the swa and know- that'd be great!
btw- I measured 7x 0.83mm diameter strands in each core- I made that 3.7mmsq- sound about right?

4mm is good for 32A unless the cable run is rather long. SWA is usually marked so that would 3core 4mm. I've never tried measuring, years of messing with cables has given me a calibrated eye!

 

[jabmesen]

thanks again Binky for your help....one last question: is it normal for 4mmsq cable to have a (calculated) 3.7mmsq cross section- just curious!

 

[Andy™]

its often stamped into the side of the cable

 

[kerching]

What did you measure each strand with? And did you take an average over various points on the strand?

 

[jabmesen]

well- I measured each strand with callipers and took an average but they were pretty much all the same, but, I only did it at the end of the cable that I stripped .....

 

[binky]

well- I measured each strand with callipers and took an average but they were pretty much all the same, but, I only did it at the end of the cable that I stripped .....

Well, you could do it in the middle, but that's probably a bad idea

 

[apprentice87]

Before you get too excited you are going to have to calculate R1 + R2 for your circuit and add it to Zs and see what you come up with. There is more to cable size than the nominal current capacity of the stuff..

john..

 

[jabmesen]

Thanks- great advice.... it runs underground is this comparable to being clipped direct?

 

[Fleeting]

Using your 0.83 I get 4.158. This is by doing the cross sectional area of each strand first then ×7.

 

[Mike P]

Before you get too excited you are going to have to calculate R1 + R2 for your circuit and add it to Zs and see what you come up with. There is more to cable size than the nominal current capacity of the stuff..

john..

Is that Zs or Ze?

 

[jabmesen]

Using your 0.83 I get 4.158. This is by doing the cross sectional area of each strand first then ×7.

Wierd... am I doing something wrong then? 0.83 so halve that for the radius ie 0.415
then square it 0.172225 then times it by pi =0.54202652
and multiply by 7 = 3.79418564.....
i was using 3.1472 for pi

 

[Fleeting]

I just cheated and used an online calculator, I think I did it correct. You must also consider the ambient temperature with such small diameters as this can greatly affect the result.
https://www.engineeringtoolbox.com/electric-wire-calculation-d_1880.html

 

[Fleeting]

Actually I have redone it at got 3.787 as you did so I must have put incorrect figures in, was sitting in traffic. Temperature may well be a factor here.

 

[poni]

Actually I have redone it at got 3.787 as you did so I must have put incorrect figures in, was sitting in traffic. Temperature may well be a factor here.

I got the same, I also think Jabmesen your PI is a little large PI=3.14159

 

[jabmesen]

I got the same, I also think Jabmesen your PI is a little large PI=3.14159

typical ; greedy when it comes to pi!

 

[kerching]

Pi was often rounded to 3.1417 NOT 3.1471
Similar to the yanks on a British yank plane coop . We worked metric, they converted ( badly) to inches and nothing fitted

 

[Davethsparky]

so the 3x4 inscription means 3 cores of 4mmsq ?

3X4 is 3 cores, none designated as an earth, 4mm conductors.

3G4 would be 3 cores, 1 designated as earth, 4mm conductors.