Calc for Cable size HELP

[mick525]

Can anybody clarify this for me I have perchest a book for solar electricity called the solar electricity handbook as i am going on a PV course in April and it has a calc in it for determining cable size (L x I x0.04) – (V – 20) = Cable csa it seems to work on (e.g. 12v & 24 & 48v) (22m x 14.08A x 0.04) – (12V – 20) =20.65mm csa but makes no sense on 230v circuits (8m x 37A x 0.04) – (230 – 20) = 1.02mm csa so if this was a shower circuit with a 8.5 kw shower running at 37A should be 10mm cable with a volt drop 1.3 not a 1.5mm cable like the calc says and also can you tell me what the 0.04 represents and the 20 which seems to be the 5% volt drop if divided by 230V which is 11.5V am i just over complicating things hear or am I doing it completely wrong when steping up the voltage all help will be appreciated. Thanks

 

[shanky887614]

different calc for dc cable size and ac.


if i remember right the guys was doing work experience before did 2 strings with 4mm to inverter then 2.5 to cuu

now this could be completely wrong this is just how they did it and they never bothered to explain

 

[moggy1968]

the solar electricity handbook is great if you want to work out an off grid system but to be hinest I think you will find it of little use for the kind of grid tied systems you are looking towards.
I found it ok for some background reading but don't get too bogged down in the minutae

 

[mick525]

different calc for dc cable size and ac.


if i remember right the guys was doing work experience before did 2 strings with 4mm to inverter then 2.5 to cuu

now this could be completely wrong this is just how they did it and they never bothered to explain

So is the calc right for 12 24 48V but not 230V or 415V Cicuits. and do you know what the 0.04 and the 20 represents in the calc Thanks.

 

[mick525]

the solar electricity handbook is great if you want to work out an off grid system but to be hinest I think you will find it of little use for the kind of grid tied systems you are looking towards.
I found it ok for some background reading but don't get too bogged down in the minutae

Thats all i got the book for is a little info befor i go on the course

 

[infinity]

What do you want to know?
Forget 12 24 48 v if your doing solar course as most voltages are around 3-400v per string! A single panel is 37v!

 

[moggy1968]

it's a long time since i read the book, but I think the 0.04 is a constant for resistance.

 

[mick525]

What do you want to know?
Forget 12 24 48 v if your doing solar course as most voltages are around 3-400v per string! A single panel is 37v!

I whould like to know why the calc wont work when you increase the voltage.?

 

[moggy1968]

it just becomes less relevant the higher the voltage is because it's a constant.

 

[SpitfireW'sale]

The following links are just an indication of dc cable sizes.

DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk

Draka Cable Sizing Calculator

 

[mick525]

The following links are just an indication of dc cable sizes.

DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk

Draka Cable Sizing Calculator

Thanks for that.