Calculating current (A) for electrical cables

i know nothing · 20 Mar 2006 at 16:57

That's the control panel I have to wire to (except I don't actually have it yet, it's being shipped at the moment).

That's the actual refiner itself.

As you can see from the pictures the cable will ultimately be connected to the control panel, not directly to the machine.

The cable run (shown in red on the picture above) is about 40-45 metres from the main distribution panel. I intend to put the control panel in question against the wall of the factory. The ambient temp can reach as high as 45 Deg C. I did not intend to use SWA as I can't see it being necessary. The cable will lay on the steel girts and girders, clipped in places (they make excellent cable trays!).

If I use cable that meets BS7211 (non armoured multi-core cable) I could just about get away with 10mm, except I need to de-rate it because of the temp (by a factor of 0.77) and voltage drop (4.92V over 45 metres). 16mm looks good.

Anybody care to calculate what size I need?

lordedmond · 20 Mar 2006 at 17:01

I would use 25 mm 3 core swa depending on run lenghth
or four core if you need the neutral

try this free demo demo

i know nothing · 20 Mar 2006 at 18:07

big_white_dog84 said:
SNIP...

So you will need a 57A cable for each phase.

I'm assuming the 'soft start' thing means your motor is not going to have a large inrush current. Even if you do have inrush the cable will have a cyclic rating that will allow a temporary over-current without burning out.

Don't quote me on this stuff though.

Found a formula here:-

It works out:-

(30 x 1000) / (1.732 x 380 x 0.8) = 56.98 Amps

So you're spot on with the 57A.

big_white_dog84 · 20 Mar 2006 at 18:37

i know nothing said:
Found a formula here:-

It works out:-

(30 x 1000) / (1.732 x 380 x 0.8) = 56.98 Amps

So you're spot on with the 57A.

Happy Days! I knew my degree would come in handy one day.