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Current and voltage ratings in dc plugs and wires? Answered

I had this great idea to turn old cell phone chargers into DC extension cords.  Cell phone wires are nice because of their curly spring wires.    I worried the wire gauge might not be large enough to handle my project.  Here is my question.  On websites that list current ratings for standard wire gauges, they list current limits but not voltage limits. Why is this?  If a 22 gauge wire can handle .92 amps does it really not make a difference whether it is 1 volts or a million volts?  Why don't they use watts to list how much power a wire can handle.  Watts take both volts and amps into account.

Another mystery is that my DC plugs are rated for 6-10 volts.  Why are the plugs rated for volts but not amps?  What would happen if I used these plugs for 4 volts, which I plan to do.  




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Best Answer 9 years ago

Cable rating DOES depend on voltage, because the insulation will breakdown if you drive to high a voltage.

Current ratings drive power dissipation in the wire = I^2 x R, where R is in Ohms/Metre

Your DC plugs are probably OK at 4V, but you may find that the resistance of the connector comes into play - and as you surmise, the power handling of the connector will suffer.


9 years ago

The voltage limit really only applies to insulation-breakdown, and that limit is to be found on some products.
Watts is directly* proportional to the wire-gauge and current, so for a fixed gauge current is equivalent.
Current and insulation should be kept separate.


*constant temperature, no magnetic-fields etc