Cable current rating advice

edit :

replying to Steve above, not Roger ,

Note that  100A , 50 degree rise case may be just about OK in a 70c engine bay type environment, as the core is now at 120C, but it is not good for the cable.

Of course in vehicles a lot of the loads are different durations - motors for windows and so on, are not not really the same as windscreen wipers, as the latter may be on all day ?.

At the other extreme we have the kilowatt audio soundblaster that luckily only draws lots of amps when the drums go bang, and has an average of perhaps 10% of the peak, but the enthusiasts pay for cables based on the peak current.


I'd be tempted, especially near batteries, perhaps with long charging periods, to double up (so twice the copper, half the rating) if there is any doubt. But it is not simple, and short of instrumenting the wire loom and then running it, the answer is really quite uncertain.

As an aside I have worked on things where we embed temperature indicating labels, so we can tell when stuff comes back under warranty if it has been abused. These have tended to show that bundled wiring runs cooler than the theory predicts, and on the other hand heatsinks do not always work as well as expected...

mike.

edit :

replying to Steve above, not Roger ,

Note that  100A , 50 degree rise case may be just about OK in a 70c engine bay type environment, as the core is now at 120C, but it is not good for the cable.

Of course in vehicles a lot of the loads are different durations - motors for windows and so on, are not not really the same as windscreen wipers, as the latter may be on all day ?.

At the other extreme we have the kilowatt audio soundblaster that luckily only draws lots of amps when the drums go bang, and has an average of perhaps 10% of the peak, but the enthusiasts pay for cables based on the peak current.


I'd be tempted, especially near batteries, perhaps with long charging periods, to double up (so twice the copper, half the rating) if there is any doubt. But it is not simple, and short of instrumenting the wire loom and then running it, the answer is really quite uncertain.

As an aside I have worked on things where we embed temperature indicating labels, so we can tell when stuff comes back under warranty if it has been abused. These have tended to show that bundled wiring runs cooler than the theory predicts, and on the other hand heatsinks do not always work as well as expected...

mike.