Help sizing cable for Farm

[cheeky_blue]

Evening all,

After a long week I've been asked to size a cable for the following:

70kva 100amp, 3 phase supply, 4 core SWA, 160m long run, buried.

Would a 50mm suffice?

Secondly, for a CPC, i was thinking to run in a 25mm alongside the armoured.
Would you agree with that?

 

[telectrix]

google "AEI cables" and register. you find a section " cable selector" . enter all your known parameters, load, length etc. and it will tell you what you need . it calculates volt drop and everything for you. XLPE SWA.

 

[Jimmyb]

Hello,

For an 100a design current you will need 70mm to get 8.8vd and min earth size is 35mm.

hope this helps could do with a little more info m8.

 

[cheeky_blue]

google "AEI cables" and register. you find a section " cable selector" . enter all your known parameters, load, length etc. and it will tell you what you need . it calculates volt drop and everything for you. XLPE SWA.

So I just tried the cable sizing wizard online and it states I only need a 35mm. Smaller than I would have expected.

Supply 415v, three phase, cable load 72kva, cable length 160m, avg temp 30 , 4 core SWA buried, based on 5% volt drop.

Gives me following:

Cable size (sq.mm):35.00Max.
current rating over 160 mtrs. 112.77
Actual voltage drop over 160 mtrs.18.42
Estimated conductor temperature (c)75.46

 

[Deleted member 9648]

Bear in mind you will need to allow volt drop on any final circuits connected to the disribution circuit,the max allowable volt drop must incude the longest final circuit as well.

 

[telectrix]

so , perehaps go with your original estimate of 50mm. should give you a bit of latitude .

 

[Graeme Harrold]

I put it through cable calc and gor 50mm with 25mm earth. This gave plenty of scope for volt drop too...........

 

[cheeky_blue]

Looks like it will be a bit more expensive then! ;-p

 

[Guest123]

Couple of things.....is it 100A per phase you're after or 100A between phases???

Also if there is any single phase lighting to be installed at the end of the sub, then you are limited by the 3% VD of 6.9V.

 

[Jimmyb]

I put it through cable calc and gor 50mm with 25mm earth. This gave plenty of scope for volt drop too...........

just wondering where im going wrong with this as i got 8.8vd with 70mm cable and thus thought proberly want 95mm, not done much sizing of three phase but have a pc program to do it for me which gave me my previous answer so could any1 explain hows it done

 

[cheeky_blue]

Couple of things.....is it 100A per phase you're after or 100A between phases???

Also if there is any single phase lighting to be installed at the end of the sub, then you are limited by the 3% VD of 6.9V.

100 amp per phase and there will be single phase lighting

 

[Guest123]

Using the Draka online calculator, to get the VD down to under 6.9V (5.92V) it comes up with 95mm 4C.

Obviously this is using an Ib of 100A which It probably wont be but as the OCPD is rated at 100A then the cable needs to be able to carry it none the less.

I took a screenshot, hopefully you can see it.

 

[andekoch]

Couple of things.....is it 100A per phase you're after or 100A between phases???

Also if there is any single phase lighting to be installed at the end of the sub, then you are limited by the 3% VD of 6.9V.

I had a similar one the other day and the advice I was given was:
allow for 5% vd since distribution cct, the 3% vd can then be applied to the light cct from the point where the light cct starts ie terminate the distribution cable in a cu and take a light cct from the cu then 2 distinctly different calcs (obvious in my opinion since otherwise most distribution cables would be 3% vd.

 

[Guest123]

I disagree with the advice you were given, VD starts at the point of origin of the supply not at the end of a sub-main.

City & Guilds use this formula in their design courses, also the ECA give this advice.

 

[m25maintenance]

i think iv jumped into the deep end of the pool here.