What amp cable best for fridge?

What cross sectional diameter was this cable?

If you have rubber double insulated flexible cable you will be able to carry 400amp at a 10% duty cycle or 135 amps at 100% duty cycle with 16sq mm cable.These ratings are for the purpose of low voltage AC-DC situations welding, automotive and battery charging systems.

Be aware that the benefits of greater current carrying capacity are not always good. Enginners design elecrtical systems with AC impedance or DC resistance in mind to assist in controlling a severe fault. In short the cable or wire should be matched to the load and the maximum number of amp able to be provided by the supply under short circuit fault conditions.

Say you have a battery rated at 600 cranking amps and you were running your fridge directly from the battery with 6mm sq TWO CORE FLAT, PVC INSULATED AND SHEATHED cable and the frigde or fridge connector developed a fault in the form of a direct short. You would be correct in assuming that the battery will try to dump it's guts into the fault because the unintelligent battery thinks that there is just more load being applied. This can cause a dangerous situation. Fire smoke and equipment damage is possible, but the length of the cable, the conductor resistance and the short curcuit carrying capacity of the cable can provide a degree of protection if matched correctly to the nominal load of the installation. The above scenario would probably see a melted plug and a bit of smaoke. Imagine the same fault carried by 95 sq mm cable which can carry 430 amps 100% of the time and short curcuit capacity will be more than 10 times that, 4300amps +. The battery will continue to feed the fault untill there is nothing left creating a very dangerous situation. A fire will almost certainly occur. A rubbed through cable of this size contacting the inner guard of a car will melt the metal.

If using heavy cables make sure you protect the cable and appliance with some sort of current limiter (fuse/ circuit breaker etc) as close as possible to the supply to avoid this type of problem.

In addition, when purchasing cable, be aware that cable is rated at carrying a certain current at a certain maximum conductor temperature (V75 and V90 are common and refer to the temp in degrees Celcius this relates only to the cable and not the method of termination or connection..terminals melt too).
The rating of cable is also determined by the installation method. Spaced, spaced and touching, exposed to sun, open air, installed in conduit are all factors which do change the rating of the cable and it's ability to shed heat. Consider the engine bay temperatures of the average motor vehicle. It could be possible that a cable could be 40 or 50 degrees or even more before it begins to carry current.......... food for thought.

Brett

Thanks for your detailed responce , i have insulated moth cable individualy and bent any metal withing its visinity and insulated that aslo . I however didn't think of fusing this cable , thanks for that, I will organise one MondayVenus Bay

Gday Steven,

Just interested in the method the dealer used to measure voltage drop. Putting a multimeter in the socket is useless unless its a second socket and your fridge is running from the first socket. You need maximum current flow through the cable to measure a voltage drop.

You need not use the fridge. A carbon pile rheostat used to test batteries or a poewr resister can provide the appropriate load to make an accurate voltage measurement. Much easier than pulling the fridge apart.

Brett,

Yeah, can't say I've ever pulled the fridge apart to measure voltage drop!!! If you install more than one socket, simply measure the other socket while the fridge is running, alternatively, unscrew the fridge plug and measure while running.

I think its best to measure it in action. That way you detect any resistance problem with the fuses, connectors etc as well.

Cheers
Phil

Whoops, I meant unsrew the socket not the plug :-)))

Good Idea Phil.

Hi,

One thing I did mention is that I use a Weaco power pack that is plugged into the point. The fridge then runs all the time off the power pack.

Whether the power pack draws differently than if the fridge was plugged in direct I am not sure.

When the Marshalls bloke tested it I remember he did not use his regular little multimeter but another larger one which then displayed 12+ volts available at the rear point. The fridge was in the lounge room at home at the time! He just said that TJMs had done a good install job and that I would have no troubles. Maybe this thing was a resistor or rheostat as suggested by Brett? As a battery dealer I would hope he would have the right tools for the job!

So far in many thousands of Kms touring it has performed flawlessly so he must know what he is talking about. I am not an auto electrician so that's why I took his advice and is why I will be seeking his opinion on the rear point in the new Prado when it is delivered. I've already spoken to him and he is only to happy to help out.

StevenLPlaydoe GXL TD Manual
It's on order, Delivery in April '04.
This pic will have to do till then. Can't wait!!!

Plain english! THANKYOU..

Sorry Chris,

Doesn't work like that. 240volts AC is a different animal. The reason why your house is wired with single strand wires carrying alternating current is that voltage drop is minimised with AC.

You're using AC wire for a circuit needing 7 amps DC. Yes you will have voltage drop. Every wire has voltage drop, especially house wiring used for DC.

TPS should stay in houses.

This is a site that gives a good insight into the Auto Electrical cables. Collyn Rivers has a very good understanding of the electrics and cable sizes and explains how to find the correct size cable for the purpose. It makes good reading also. The URL is
http://www.motorhomesaustralia.net/cable.html

Keith

Thanks Keith,

That is a very good website, i am happy i am not going to have a meltdown. Cheers..