# Choosing cables for high amperage

I'm having trouble choosing a wire gauge for a project I am working on that uses high amperage (100A) at 14.8V. From what I have read here, I think have to use at least 6 AWG to handle it.

What's confusing is that I also have a hall sensor rated for 200A that only uses 10 Gauge wire. Is it ok to use the higher (ie. thinner wire) gauge when working with shorter distances? Or will the hall sensor wires burn up when they exceed 55 A?

My project may consume up to 1480 W of power from a battery I have. If I am only running short distances (if this makes any difference at all) of about 20 - 30 cm is is safe to use the thinner 10 AWG wire? If not, which wire should I be using?

I am very new to electronics but I am willing to learn. Please don't hesitate to ask me to elaborate on anything.

[EDIT] My hall sensor: http://www.mauch-electronic.com/50a-100a-200a-hall-sensor

• Gauge will depend on tolerable voltage drop, temperature rise, power loss, etc. The longer the wire, more voltage will drop and more power you will lose. Contact resistances could possibly play a role if not taken care of. You have to decide how much power you can lose, and then decide if 10AWG is ok for ~30cm run (if it can survive the temperature rise). Oct 6 '17 at 20:12
• You should provide a link - in your question - to the datasheet for the Hall sensor so that we know what you're talking about. "1480 W of power" is like saying "11 inches of distance". The watt is the unit of power so we just say "1480 W". Welcome to the world of electronics. Oct 6 '17 at 20:15
• @Wesley Lee Do you know any explanations that show you how to calculate the rise in temperature over distance? Oct 6 '17 at 20:15
• @Transistor I have added the link to the hall sensor as you have requested. Oct 6 '17 at 20:16
• Looking at the way that stuff is built, I have to ask if it's designed to operate in a fairly high speed airflow... it may normally rely on that for cooling. Would that be the case for your installation? Oct 6 '17 at 20:19

What's confusing is that I also have a hall sensor rated for 200A that only uses 10 Gauge wire. Is it ok to use the higher (ie. thinner wire) gauge when working with shorter distances? Or will the hall sensor wires burn up when they exceed 55 A?

There are two considerations for correct selection of wire guage:

• Acceptable voltage drop along the wire. The smaller the cross-section the higher the resistance and the voltage drop.
• Acceptable temperature rise as a result of power dissipated in the cable's resistance.

You should be able to work out the first from cable gauge resistance tables.

The second is a bit trickier. You can work out the wire resistance per unit length and work out the power dissipated per unit length from $P = I^2 R$. The heating will cause the temperature of the wire to rise until the heat lost to ambient = resistance heating. What temperature this occurs at depends on the wire insulation, the ambient temperature, air-flow, etc., so it's difficult to work out from first principles. You might get some ideas from multicore cable ratings or conduit cable ratings where the inner cores are not exposed to free air.

• Thanks for accepting my answer but I suggest you unaccept it for a day or two to give others around the rotating globe a chance to answer. I've explained some theory. Someone else might actually answer your question! Oct 6 '17 at 20:34

Yes, as the cable gets longer it will matter more. A car battery delivers maybe 100 amps at 12V when starting, but the cables are usually under a foot long so - even though it is heavy wire - it doesn't need to be very heavy wire.

As others have noted, it really depends on (1) the impedance of your load; (2) how much voltage drop you can tolerate (which itself is a function of the resistance of the wire and impedance of your load), and (3) how much heat you can tolerate coming off the wire.

It is hard to say given the info. If you need to run 100 amps from a car battery to a low impedance load (roughly 1/8th ohm) and it is in the next town, you are going to need a very larger cable - even if the wire is buried under frozen earth to take up the heat.

You've already linked an excellent table which lists resistance per foot/metre. From there, you can derive voltage drop, and think about how that will affect your application.

You can also look at the National Electrical Code tables (310.15) to get a sense of how much heating will occur in the wires. For instance 6 AWG at 75A continuous is expected to be 90 degrees C. At 100A it will get warmer still.