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Measuring AC phase Question

I understand I am to reverse the plug in the AC outlet and measure from a known ground, in my case, a galvanized water pipe, and the positive probe is connected to the equipment chassis. I use a cheater plug on the power cord to allow reversing of the orientation. No other cords are connected to the equipment being tested.
You are supposed to choose the position of the cord that yields the lowest ac voltage on the chassis when the unit is on.
The problem I have is that the lowest voltage with the switch on also has by far higher voltage on the chassis when the power is switched off.
badge
bob_bundus
1,834 posts
 
determine the best phase connection, then rewire the outlet, if necessary, to reverse phase internally. This eliminates the ground cheater adapter & the chassis will always be at ground potential, theoretically reducing stray measured leakage voltage to zero. Label the outlet prominently so that you don't accidentally forget that the hot & neutral slots are inverted. This could be a safety or liability issue in the future. Disclaimer: I am not (professionally or otherwise) advising that you invert these electrical connections. I am only "answering your question". I'm sure that you understand what I'm implying.
bigtee
803 posts
 
Purchase a cheap phase polarity meter and check it. These can be bought at Sears, Home depot, etc. They also have a ground orientation mode. Remember, AC has 1 hot leg(usually the black wire), 1 neutral(white) and a ground. The neutral is tied to the ground buss along with the ground but they are not the same thing. Reversing the polarity can create problems sometimes. The switch on the unit generally opens the black wire. If you reverse it, it now opens the white. It something unexpected happens, the chasis of your unit could remain hot(worse case scenario.)
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