Earth cable size

[Mark Wilson]

Does the earth return from a heated window have to be the same size cable as the feed? I've some nice flexible conduit I'd like to use to house the cabling to the screens in my traveller's rear doors, but it's just too small for two runs of the chunky wiring I've used for the feed (from memory I think this is 20A, could be more). As you may have guessed, I'm no electrical engineer, but I'm thinking that all those electrons being converted to heat should reduce the amount of current needing to find it's way to the chassis earth. Or am I being simplistic?

[geoberni]

What goes to it, has to get back from it.
The electrons aren't converted to heat, they're agitated; the heat generated is a side effect of squeezing all that power through a small conductor.
Use a smaller cable and you're just going to make an additional Heater....

[Mark Wilson]

That's very useful and educational, thanks. As I sized the cable for the front heated screen, I think I'll redo the math and reduce the final cables from the point the circuit splits to the two rear windows. Anyone happen to know the load for a single traveller window?

[oliver90owner]

My question is: Why?

The earth return for most of the electrics, including the starter motor, is via the car chassis, so why can you not just use that?

[Mark Wilson]

Unfortunately, the wooden frame of the Traveller isn't too great at conducting electricity! The earth has to be taken from the door via a flexible cable down to the steel chassis in the bootwell.

[geoberni]

That's very useful and educational, thanks. As I sized the cable for the front heated screen, I think I'll redo the math and reduce the final cables from the point the circuit splits to the two rear windows. Anyone happen to know the load for a single traveller window?

I'd ask whomever supplied them. Otherwise, get a multimeter and see what resistance they are.
My guess would be current requirements in the region of 6 -10 amps.