2. misc-audio
  3. 1050449527

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.
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Showing 2 responses by bob_bundus

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.
bob_bundus
1,834 posts
 
First, are you measuring the equipment in isolation? That is: nothing else is connected to the component being tested
that question is already answered in the posted text.

If you decide to go inside the equipment instead, then annotate the mod such that it can be reversed later before any future sale - otherwise it's now modded / nonstandard equipment with diminshed resale value & may not pass the U.L. If it blows up later then this could come back to haunt you.
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