On March 17, 2016 at 18:59, Ernie Gilman said...
A friend is on site in Mexico working on an A/V system. The power is split phase.
He measures 228.7 volts from phase to phase. That's running the projector. But he also measures 129v on one phase and 128V on the other phase (presumably to neutral!). Whenever we've measured split phase power in the US, the two phases to neutral add together to the phase to phase voltage.
Any idea what's happening here? Is it possible that the two phases are less than 180 degrees out of phase?
Thanks.
Did they measure to the actual grounding stake (do they even use them?) that was driven into the ground as their reference? In DC circuits with batteries, the battery posts are the point of reference, not the cable clamp.
Was this measurement taken at the projector, or at the breaker/fuse panel? If at the breaker, I would recommend the other as an additional test because it really seems that the wiring has some resistance that shouldn't be there- possibly from bad connections at an intermediate point.
Do they have any three-way switches? Make sure they're not switching the neutral. If one of those is leaky/switching the neutral, it would be possible for AC from one phase to coincide with the other, bucking some voltage.
What voltage should they have seen, under normal conditions? If the building has metal siding with a three-way switch in a metal junction box, tell them to be careful- I got a few good jolts from my parents' garage, due to the three-way switch switching the neutral and making the box hot when the switches were in a particular position.
