On 2014-05-07 13:48, James Knott wrote:
Per Jessen wrote:
"An example of application is a local distribution in Europe, where each customer is fed a phase and a neutral." The difference in North America is instead of using one phase to the customer, a transformer is used, with the secondary centre tapped to ground, with the two hot wires 180° apart. With this method you could say 6 phases are available.
Ah, that's explains some things for me, thanks. No, it is 3 phases (look at the waveforms with a scope), but each one is split in half voltages. Interesting trick. The reason for the three phase distribution is that you can carry more current with less copper (4 wires instead of 6 for the same total load). The method you describe has to be short distance, and provides the advantage of having two voltages in the house, normal and "heavy duty". A 110 AC line is less dangerous for electrocutions, but worse on heavy loads because of fire risk (higher current). In the three phase method, the neutral line, although connected to ground at some point, should never be used as such. It can carry current, and ground voltage is not ensured. Using the ground to carry current causes, at least, corrosion problems. And might kill horses! ;-) In Spain houses can only get a live and a neutral. Which "live" of the three is different for each home. Getting two lives is forbidden, although I have seen it used because many years ago we had 220 three phase instead of 380. Houses were 127 (IIRC), and some were 220 with the 2 phase trick. By the way: 220 = 127 * squareroot(3) 220 * sqrr(3) = 380 That's the explanation of our voltages choices. About the "Ground Fault Circuit Interrupter" thing, in Spain is mandatory for the entire house; we call them "differential switch". If the current on both wires is not the same (max diff 30 mA), it means that some is leaking to ground, possibly via a human body, and trips. <http://es.wikipedia.org/wiki/Interruptor_diferencial> -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar)