AWG amp rating chart, what about voltage?

rg12 · Mar 25, 2019

I'm looking at the chart of how many amps are recommended as constant current for a certain wire gauge and the thing is that nothing about voltage is mentioned.
I think if a wire is rated 40A constant that it will be totally different if it's a 12V or 240V.
Am I missing something?

Punx0r · Mar 25, 2019

Voltage doesn't matter to the current carrying capacity of a wire - only amps cause heating (P = I^2 x R).

Voltage only comes into a wire rating in regards what the insulation is rated for. I.e. bell wire is no good for mains voltage.

spinningmagnets · Mar 25, 2019

The major concern for voltage (as I currently understand it) is that higher voltages can have a spark jump a longer distance through the air. Therefore...the prongs on the plugs are farther apart.

On that same note, most electronic chips run off of 5V so that the traces can be very close together.

marty · Mar 25, 2019

https://science.howstuffworks.com/environmental/energy/question501.htm

he three most basic units in electricity are voltage (V), current (I, uppercase "i") and resistance (R). Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.
A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.

This was explained to me by a guy who is older then plumbing pipes. He say amps is like the size of the river. Volts is the speed that the water is flowing.

spinningmagnets said:
The major concern for voltage (as I currently understand it) is that higher voltages can have a spark jump a longer distance through the air. Therefore...the prongs on the plugs are farther apart.

On that same note, most electronic chips run off of 5V so that the traces can be very close together.

That's how spark plugs work. It's not the volts that hurt you. What hurts is when you bang your head on the hood.

rg12 · Mar 25, 2019

I understand that the amp cause the heat but still, higher voltage means that amps travel faster thus creating more heat than lower voltage right?

Punx0r · Mar 26, 2019

Nope!

The heat (watts) generated in any length of wire is P = I^2 x R

Alternatively the same value can be calculated as P = VI but the volts here is not the system voltage but the voltage drop along the section of wire you are measuring, which is caused only by the resistance, so V in the second equation is just a proxy for R in the first equation.

rg12 · Mar 26, 2019

Punx0r said:
Nope!

The heat (watts) generated in any length of wire is P = I^2 x R

Alternatively the same value can be calculated as P = VI but the volts here is not the system voltage but the voltage drop along the section of wire you are measuring, which is caused only by the resistance, so V in the second equation is just a proxy for R in the first equation.

but higher voltage means more "friction" due to resistance in the wire which means more heat, it doesn't matter due to what but the bottom line is that at a higher voltage more heat will be generated, especially in a long wire, right?

Voltron · Mar 26, 2019

It does affect it. But they can't know what voltage you're going to run at. The point of using the chart is you need to know your system wattage. When you know that, you divide out your personal system voltage you'll be using to get the amps that will be flowing. Then you get the wire size you need with the voltage already calculated in.
That why it isn't in the chart... You already have to take the voltage into account to get the amp flow required for a certain power delivery.

rg12 · Mar 26, 2019

and what about exceeding the rated constant amps? each wire also has a rating for how long you can run for bursts of 10s, 5s, 1s which is dozens more.
Meaning that the wire can transfer any amount of amps but at the cost of heating, right?

Matador · Mar 26, 2019

For for higher voltage, gauge doesn't need to be different all current (amperage) being equal. What matters is this keyword "insulation". You ne to have propern insulation rating. Air can conduct high voltages through arching. This is why you see oil in high voltage trnasformet... Cannot let air conduct through arcing or you'll create a short !

Matador

Punx0r · Mar 27, 2019

rg12 said:
but higher voltage means more "friction" due to resistance in the wire which means more heat, it doesn't matter due to what but the bottom line is that at a higher voltage more heat will be generated, especially in a long wire, right?

Nope!

The "water" analogy for electricity can be confusing. The "speed" of electricity (the signal or wave velocity) doesn't change with voltage. Higher voltage is like a greater force that can drive higher current through resistance. But for a fixed current heating is exactly the same.

rg12 said:
Meaning that the wire can transfer any amount of amps but at the cost of heating, right?

Yes. An infinitely thin wire can carry an infinitely large current as long as the time duration is infinitely short.

rg12 · Mar 27, 2019

So bottom line 100A at 12V and 100A with a 1000V equals the same amount of heat through the wire?

Punx0r · Mar 27, 2019

AWG amp rating chart, what about voltage?

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