cable current capacity(ampere)

Hello guys,

I have just finished making my set of car jumper cables using 300AMP

35mm square fine strand copper cables. These are orange in color and preety think. they are Orange Welding cables actually.

I just like to know, how come the cable is only rated at 300amp when it's so think, 35mm?? That's equiv to 2AWG. I've seen thinner car jumper cables being sold with 400amp rating.

Ok my guess is that my cables can withstand 300amp sustained current whereelse those sold off shelves are rated for the peak current which it wouldn't last after a few seconds of cranking the car's engine?

So how much current can my cables actually carry across to jump a car? Since they are so think and powerful can they be used to jump start large diesel engines like a lorry?

Thanks.

Reply to
Brian Su
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The whole issue of current-carrying capability of conductors is chronically oversimplified.

At the simplest level, there is what the US NEC calls the ampacity, which is the amout of current the conductor can carry continuously under specified conditions without exceeding the temperature rating of the insulation. This is strictly designed as a fire prevention specification and has nothing whatsoever to do with the suitability of the conductor for a purpose. For example, if you install a cable of 1,000 feet of AWG 14 wire, and load it to its NEC load of 15 amps, the installation will be safe but won't work, the voltage drop will be excessive and the equipment at the receiving end will not function properly.

In you case, however, the converse is true. For the very short periods where a jumper cable actually carries current, heating is not an issue, but voltage drop IS. The rating in your case is probably the current the cables can handle without causing the voltage to drop to the point where they are ineffective. Or, the ratings could just be sales puffery. #2 AWG will carry a lot of current for a few seconds, which is all it takes to start an engine. How big is the battery cable in the vehicle? I bet it is no bigger than your jumper!

I wouldn't worry about burning up your cables. Try them on the lorry. If they work, good, If they don't due to excessive voltage drop, it won't matter!

Reply to
BFoelsch

Hello, thanks for your time explaining stuff. Yes the battery cable in the vehicle may be smaller or of the same size as my jumper leads but they only run for a feet or 2 to the chasis/starter motor. Wherelse my jumper cables run for 2.5 meters each. The other thing is that, battery cables in the car are normally think strand copper cables made up of about 15 - 20 strands of thick copper wires in them. I believe thick strand cables can carry more current than thin strand ones?

Yeah I don't think these welding cables can be burned up just by jump starting a lorry. I'll be suprised if they overheat at all... hehehe.

Thanks.

Reply to
Brian Su

Once you get over 4AWG the clamps are likely to be the weak link.

Reply to
Greg

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