when connected to mulitple switchboards i get a reading of 155v red to ground,4v white to ground and 153v blue to ground. When i disconnect main switchboard and have nothing connected to the tranny my voltages from each leg to ground are as above
Draw yourself an imaginary circle around the transformer, like a fence..
That fence represents the insulation of the transformer.
When you connect a voltmeter from one transformer phase to earth, you let a trickle of current flow out of transformer, through meter and over your fence into earth.
Apparently one of your switchboards connects white phase to earth.
So you get solid readings then, the meter current returns to transformer from earh via white phase.
But -How does that meter current get back into transformer when you've disconnected white phase from earth? How can it jump the fence?
It can't.
That's why you get flakey unbalanced readings, only a fraction of your meter current finds its way back over the fence. Insulation is imperfect and your meter is too sensitive.
Use a less sensitive meter and you'll read nearly zero on all three phases.
Or use a lightbulb instead of a meter.
it's a common problem ever since high impedance DMM's became so popular.
Typical DMM is 10 meg input.
Simpson 260 is i think 5Kohm/volt on AC, so on 250 volt scale = 1.25 meg.
A 1 kohm per volt el cheapo meter is what you need for that measurement.
Check the little yellow $ 9.95 GE analog meter at Walmart.
old jim
