How thick should my electric wire be?

[demonboy]

Is there a formula for working out how thick my electric cable should be, based upon length and ampage draw? I'm installing a water-maker that claims to work at 9amps on 12v and the distance between the unit and the batteries is approx 10m (taking into account bends and bulk-heads etc). I'm trying to use existing cable and holes but worry that it may be too thin.

Thanks!

 

[PetiteFleur]

Here is a table that I use - http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html
Don't forget you have to use the 'there and back distance' for the calculation.
Vics might be along to give more details.

 

[Boathook]

Could try this site
http://www.energyforce.co.uk/cable.html

In the past I have gone for the thickest that a standard crimper will do, 6mm square ....

 

[PetiteFleur]

Thats good! I've bookmarked it for future use.

 

[demonboy]

Like it. Thanks for that - also bookmarked.

 

[npf1]

BTW: the current draw will be higher as the motor starts, which might require larger wire than that required for 9A.

 

[neale]

Depends upon what voltage drop is acceptable. Some things, nav lights and distribution boards should be no more than 3%. Other less critical items can deal with as much as 10% voltage drop.

Also depends on ambient temperature where the wires are run and if the wires are run in conduit, bundled together or singularly.

If it were me I would probably use 6mm2 which will give you around a 4% voltage drop at 9A assuming ambient temps of below 35°c with cables not run in conduit.

 

[seanfoster]

That calculator is really useful, should you use 'there and back' for this calculator too? (i.e for a masthead light, that is say 15m from battery to bulb, would that be 15m or 30?)

 

[st599]

Remember you also need to de-rate because these equations will be for a single conductor/conductor-pair surrounded by air.

 

[Boathook]

I am not sure above the there and back. Some calcs allow for it and others don't. The site I gave I would have to double check any 'instructions' given. /forums/images/graemlins/blush.gif

 

[Anonymous]

All the advice you've been given is fine but if you have bought a proprietary watermaker I'd email the support department and ask them what they recommend. There should be a wiring diagram showing appropriate fuses, switches or breakers, as well.

 

[VicS]

[ QUOTE ]
I am not sure above the there and back. Some calcs allow for it and others don't. The site I gave I would have to double check any 'instructions' given


[/ QUOTE ] The Engineering Toolbox table requires a there and back figure to be entered for the cable run length.

The EFI calculator is based on a 5% voltage drop so I would not use that one. The basis of the cable run length is not stated either.

THIS ONE is based on a 3% drop (although that can be altered to 4% or 5%) It does not require the cable length to be doubled up to give a "there and back" figure

 

[demonboy]

Thank you once again all. I particularly like the last link, Vic, as it explains things very well.