DC cable size calculation

[Spoon]

Hi people,

Please can you help. A college at work is asking about what size cable to use for the below:
12V supply, 40A, 2 meter run and 5% acceptable loss
There are lots is sites out there which I have seen, but when inputting the info I get from 6mm to 10mm and none of them tell me the formula of how they got this size.
I havent done any calcs for 12V before so any help would be greatly appreciated.
What is the formula for calculating the cable size for a 12V system?

Ta
Spoon

 

[Engineer54]

Hi people,

Please can you help. A college at work is asking about what size cable to use for the below:
12V supply, 40A, 2 meter run and 5% acceptable loss
There are lots is sites out there which I have seen, but when inputting the info I get from 6mm to 10mm and none of them tell me the formula of how they got this size.
I havent done any calcs for 12V before so any help would be greatly appreciated.
What is the formula for calculating the cable size for a 12V system?

Ta
Spoon

The same as you would use for a 230V calculation, substituting the 230V with 12V!!!

 

[Spoon]

The same as you would use for a 230V calculation, substituting the 230V with 12V!!!

Thanks for the quick reply Eng54.
I've always used the cable data or reg tables, e.g. Table 4D2A, to pick the cable size for AC circuits. I do not remember ever using a formula to calculate the size, so its hard for me to substitute the 230V with 12V.

 

[Engineer54]

The current carrying capacity of a cable is the same whether you are at 12V or 230V. So if you know the current (40A) then you can check on a suitable sized cable. The problem with 12V, is the huge difference in VD compared to the normal 230V.
Having said that, 2 metres isn't going to make too much of a difference... Again NO difference in AC or DC current for the sort of thing your looking at!! Cable size will depend very much on the type and the installation method used. Remember the 5% losses, is 5% of the 12V, so the minimum voltage at point of utility will be 11.4V... so the mV/m figure will be the critical factor.

What's this for anyway??

 

[Spoon]

Again, thanks Eng54. Apparently the colleges daughter is designing an electrical clutch control for a car. They are using quite a big solenoid and this is what the cable is for.

 

[Engineer54]

Again, thanks Eng54. Apparently the colleges daughter is designing an electrical clutch control for a car. They are using quite a big solenoid and this is what the cable is for.

Then she will be using fine multi stranded auto cable, which i have no data on. Check with a local auto electricians outlet, who will be able to sell her the correct sized cable for the job!! lol!!

 

[Spoon]

Thanks for all your help Eng54.

 

[jeremy]

Have a look at the Eland website for tri rated cable current carrying capacity. It gives the max current capability, but also the Volt drop in mV/A/m. 4mm would seem to be the one you're looking for. We use this type of cable a lot; it's very easy to work with, but needs to be terminated properly to avoid damage to the strands.