Tim Attwood wrote:
>> 1. A car runs on 12V electrics, not 250V. Does that make a difference?
> 
> Yes, lots. Voltage is the size of the elephant, amperage is how fast he's
> going when he runs you over. I think many cars will pull more than 100 A
> cold starting though.

No, not for the sizing of the cable. If the cable has resistance of
0,01ohms and the current is 100 A, the cable will heat up with
100^2*0,01=100 W (P=I^2*R) and hold up 100*0,01=1 volt (U=I*R) of
voltage (this 1V is called the voltage loss of the cable). Rest of the
voltage (11V or 249V) will get to the final device and it'll have matter
there.

Practically everyone/-thing (lets say house heating, 10kW) needs power
(P, measured in watts). While P=U*I, we can produce 10kW of heat eg.
with either 1A*10kV, 10A*1kV, 100A*100V, 1kA*10V or 10kA*1V. If the
transmission lines to the house adds up with 1ohm, we'll heat the
transmission lines up with anything from 1W (1A^2*1ohm) to 100 000 000 W
= 100MW (10kA^2*1ohm). This is why the main transmission lines do not
have 230-400V voltage, but ~10-400kV voltages instead - to minimize the
power loss, which only heats up the outside air.

> 100 A * 12 V = 1200 W (~1.6 hp)
> 100 A * 220 V = 22 KW (~29.5 hp)

True, at the final device.

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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