basic electrical question

[ralph5]

Using watts law

15. a x 120v = 1800w
    
75. a x 24v = 1800w
    
    

So can i put 75a of 24volt throgh an extension cord rated for 15a of 120volt?

Or is the amp rating just that, no matter the voltage?

[wooferhound]

The amperage for wire will aways stay the same

you can only get 15a of 24v through that wire

or you could make 5 runs of that wire

hook it all together and then you could get 75a through it.

[Flux]

Yes but it will smoke and burn out quickly and you may get little of your 24v at the end.

You are confusing power with carrying capacity.

The rating of 15A is based on safe temperature rise. The 120 v is its accepted rating or its intended use rating, the cable may actually be capable of safely standing higher voltage.

At low volts the insulation is no issue but the current should be limited to 15A to prevent excess temperature. You may have to keep the current well below 15A to stay within a reasonable voltage drop.

The maximum load you can reasonably use at 120v is 1800W. The maximum safe rating ( long term) at lower voltage will be the voltage x 15 but you may only manage a fraction of that if volt drop is an issue.

Flux

[ralph5]

I didn't think so. Just wanted to make sure.

[wpowokal]

The only stupid question is the you do not ask.

allan down under

[finnsawyer]

No.  If the resistance per foot of the cord is Rl, then the power loss per foot, which shows up as heat, at 15 amps is 225xRl.  If you run 20 amps through the cord the loss becomes 400xRl, so the cord will tend to get warm.  At 75 amps you get 5625xRl, and probably burn the house down.  Now in reality the current rating is rather conservative, because the manufacturer realizes that there is a strong possibility that someone will run the cord under a carpet.  But 75 amps is out of the ball park in any case.

[AbyssUnderground]

Wise words.