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Unread 22-09-2014, 04:14
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Aren Siekmeier Aren Siekmeier is offline
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Re: Electrical basics

Quote:
Originally Posted by Michael Hill View Post
Hey, could you shed some light on current/power ratings for me? Something that's always confused me are ratings at high voltages. These say they're rated for 32 Amps @ 400 Volts. Are these the maximum for both current and voltage? That is, you should neither operate above 32 Amps OR 400 Volts? Or is it it a power rating? That is, it's rated for 32 Amps * 400 Volts = 12.8 kW. Or is it a P=I^2*R power? In that case, the current would be the max current no matter the voltage
The current rating of a conductor is itself a power rating, basically how much power can it dissipate as heat. The power dissipated as heat is indeed P=I*V, but this V is the voltage drop across the conductor, not across the load the conductor leads to. The voltage drop across the conductor is given by V=I*R for a conductor resistance R, the power rating is P=I*V=I^2*R, and depends only on the current and the physical characteristics of the conductor (size, resistivity, length...).

The voltage rating of the device is the max voltage before the insulation between conductors or between a conductor and the outside breaks down and allows a current. This is entirely a function of the various dielectric and insulating materials being used between conductors and the electric fields they can withstand before ionizing and carrying a current. The current carried by the insulating conductors has no effect.

So these two ratings are unrelated. You should not exceed either of them, even if you are way under the other one.