Wire Size

[superg]

Hi Guys what GA wire should i use to run from my aux battery to the rear off the car to run my fridge, lights etc from? Is 8GA thick enough? thanks

[drivesafe]

Hi superg, if by lights you mean camp lighting which uses around 1 or 2 amps while powering a fridge at the same time then 8G cable ( 7.9mm2 ) will be fine.

If on the other hand the lights are spot lights then, depending on the size and number of lights, you will need to go to at least 10mm2 or 6G ( 13.5mm2 ) to reduce the amount of voltage drop which will in turn keep your spot lights fairly bright.

Cheers.

[superg]

thanks for that mate, much appreciated.

[Turbz]

Is there an equation to work out what sized wire you require ?

[drivesafe]

Hi Turbz, you can try to do the calculations yourself or you can do it the lazy way ( I do ).

Try the link bellow.

Cheers

http://www.currentsolutions.com/knowledge/vdrop.htm

[Oscars]

length x amps x 0.017 \ cross section area=Vd

6 b&s,at least is wat i normaly run

[Turbz]

ooh.. nice work. I LIKE IT I LIKE IT!

[j-top paj]

run the bigger the better
never know when u need power in the rear for other things like inverters etc...
no point runing more than one cable or re-runing it

[fool_injected]

Run 4G (100A)
8G has a 50A rating
Protect it near the battery with a curcuit breaker
http://www.jaycar.com.au/productView.as ... BCATID=461

Then run a fuse block in the rear
Over 20ft if you draw 90A its only 0.43 Vdrop but that's ignoring the temperature coefficient
http://www.cirris.com/testing/temperature/copper.html

[drivesafe]

Hi fool_injected, when selecting the size of cable, bigger is usually better, however, the exact reverse is the case when selecting the correct size fuse or circuit breaker.

Many people make the potentially lethal mistake of installing too high a current rated fuse or circuit breaker. The thinking that, if the cable can carry 100 amps then the protection should be either a 100 amp fuse or circuit breaker is a BIG mistake.

When designing high current circuits, for a starter, use circuit breakers, as these are much safer because circuit breakers have a better response time to higher currents than fuses do.

In either case, something like a 100 amp fuse or circuit breaker is designed to be able to handle around 150 amps for nearly 1 hour before blowing or tripping and can handle something like 400+ amps for a few seconds before tripping.

This high current handling is deliberately designed into these devices to allow them to handle the near dead short that occurs every time an electric motor starts, IE like your fridge’s compressor motor and your portable air compressor’s motor and the split second high current surge that occurs when you turn your lights on. Some driving light globes can cause as much as a 100 amp spike when they are turned on.

In most dual battery set-ups, no matter what type of Auxiliary battery is being used, a 30 amp circuit breaker will be quiet adequate.

In engine bay installations where there is a short wire run, one circuit breaker, anywhere along the positive cable will do, but where the auxiliary battery is mounted somewhere else, IE in the rear of the vehicle or in a trailer or caravan, the you need to mounted a 30 amp circuit breaker at either end of the positive cable, near each battery’s positive terminal.

Using this sort of set-up not only gives you much safer protection in a dead short situation because the 30 amp circuit breaker set-up will not only trip much MUCH quicker ( the 100 amp will probably work but may actually take a few seconds to go open circuit ), the 30 circuit breaker set-up also gives you overload protection. The 100 amp set-up in an overload situation can actually allow the cables to melt and still not go open circuit.

[fool_injected]

The breaker I was refering to with the relation to the metioned cables is correct, IMO, however the margins are fine
The 100A breaker will trip @ 110A or immediatley if short curcuited.
http://www.jaycar.com.au/productView.as ... &SUBCATID=
The 4 GA is rated at 110
http://www.jaycar.com.au/productView.as ... BCATID=491
you are right is saying smaller is better and that said the 70A breaker would be a safer option (it can still handle 90A surge for 1 minute) which I will use and include in my other thread http://carl.outerlimits4x4.com/viewtopic.php?t=103306
Appreciate the advice it made me think a little harder