Shorepower

[Carioca]

"The whole issue may be side-stepped by installing an Isolating Transformer."

Not quite, specially if your boat is on the hard.
The grounding plate on the hull will be required to discharge through .........the air ?

[jehardiman]

Originally Posted by M&M Ovenden

Hi Jehardiman,

I'm not sure you are completely correct of your assessment of North American grid power. I think we should look at the two major areas that power is used; industrial (3 phase) and 'home or small business' (single phase) .

You are correct, in low density power areas residential and lighting is 240/230-120/115 3 wire pulled off one of the phases in a transformer (with an inversion to get two phases out) of the high voltage 3 phase distribution lines. Here on the shipyard and in large bulidings/high density power areas it is 220/208-120 4 wire. But then again, it depends on who you ask wether 208/220 and 230 are called 240 and 115 is 120 (i.e. in a "120" volt system the peak voltage is 170, the rms voltage is 120 and the current rating voltage assumes a 5% loss for a voltage of 114).

[M&M Ovenden]

Originally Posted by jehardiman

Here on the shipyard and in large bulidings/high density power areas it is 220/208-120 4 wire. But then again, it depends on who you ask wether 208/220 and 230 are called 240 and 115 is 120 (i.e. in a "120" volt system the peak voltage is 170, the rms voltage is 120 and the current rating voltage assumes a 5% loss for a voltage of 114).

Hi,

I realize that most people consider 208/220/230/240 the same voltage, but to do so is sloppy. 220/230/240 is from a single phase source, where 208 is from a 3 phase supply. if 220 was from 3 phase power each leg would have a voltage of: 220 / (2*sin120) = 127V . In your shipyard you will find that you have 3 phases of 120V, which gives a phase-phase voltage of 208. This can fluctuate from location to location, but the voltage ratios will always be the same.

Cheers,
Mark Ovenden