On 03/16/2011 12:23 AM, Peter Blodow wrote: > Hello Kirk, > I don't see why you should not be able to measure your mains phases with > an ordinary oscilloscope, set up as usual. At least in this country, the > three phases of mains current are ground referenced, 230 V effective > voltage to neutral. Between the phases, as can be figured with a > triangle formula or by trigonometry, there are 400 V eff. (not ground > referenced, of course). Connect each phase with a high resistance probe > or, if exact magnitude is not important, with a small capacitor. It's > just measuring a ground referenced voltage, a little higher than usual, > but still. No floating oscar, as long as you don't want to measure > differentially between phases. > > I think what he is trying to do is move the scope common the the center-tap point of the motor. When using a 2-phase to 3-phase converter, the motor's center point is NOT at ground potential. This is also true when using several of the unbalanced 3-phase supply systems available in the US, such as corner-grounded and center-grounded open delta supplies.
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