Cable Calc.

[Spudnik]

Would one of you helpful chaps do a cable calc for me, as i dont have my books to hand at the moment as i am away.

40A over 100 meters. Most of it SWA.

Much obliged

 

[scotsparky]

what you after mate? volt drop CCC ?

 

[Spudnik]

oh yeah

volt drop & CCC/size ta.

 

[scotsparky]

just out shower give me 10 mins

Single or 3 phase? whats the erection method ambient temp ect

 

[Spudnik]

Single Phase.

Its for a garden office, so SWA buried.

 

[Mark.W]

Hello mate

Can you tell me what breaker you're using, also I take it 40A is your design current?

 

[scotsparky]

as its burried its a 10mm mate!
6mm just far to tight

 

[Mark.W]

I got 16mm cable the ccc will be 91V and your VD would be 11.6V so just borderline @ 5.04%

I calculated that on 10mm cable the VD would be 18.8V which is 8.17% (above the 5% allowance)

Hope this helps

 

[saveloy]

I got 16mm cable the ccc will be 91V and your VD would be 11.6V so just borderline @ 5.04%

I calculated that on 10mm cable the VD would be 18.8V which is 8.17% (above the 5% allowance)

Hope this helps

Please correct me if I have this wrong, but with a VD of 11.6/ 5.04% this will not leave any allowance for any lighting to be installed in the office as the max permissible VD for lighting is only 3%. It is also on the limit for power circuits and this is only the supply to the dis board (without circuits installed).

 

[Mark.W]

Please correct me if I have this wrong, but with a VD of 11.6/ 5.04% this will not leave any allowance for any lighting to be installed in the office as the max permissible VD for lighting is only 3%. It is also on the limit for power circuits and this is only the supply to the dis board (without circuits installed).

I used a total design current of 40A including power and lighting! So what would you suggest then possibly take it one up to 25mm?

 

[saveloy]

I used a total design current of 40A including power and lighting! So what would you suggest then possibly take it one up to 25mm?

I see what you are saying. TBH I didn't do any calcs I just saw the 5% Vd and I am a bit unsure as to how the 3% for lighting affects the calcs. I will do the calcs etc as I would do them inc VD for the ccts, and post them up for people to look over and pick holes in etc. I may be some time!!

 

[Mark.W]

I used a total design current of 40A including power and lighting! So what would you suggest then possibly take it one up to 25mm?

The way I have always done it is to calculate the VD & CCC for the cable up to the office with a design current of 40A. I would then design the circuits in the office seperately so 3% for lighting and 5% for power. Hope that makes sense?

 

[Spudnik]

ok peeps here is the situation.

I have roughly estimated a 40A submain for a garden shed office.

Its only going to have a few PC bits and pieces, lighting and more than likely a panel heater.

I have in mind a 40A MCB radial, although im sure a 32A would suffice.

Basically, i dont really want to have to run 16mm SWA

 

[Mark.W]

The problem is the 100m run, so I think it will have to be 16mm mate TBH, with a 10mm the VD over 100m is just too mcuh!

 

[Spudnik]

Ah well, 16 it is then.

Mind you, i might be able to persuade him to move it up the garden a bit and try to reduce the run.

That is one trench i will NOT be digging