Do you remember this Conversation
I ran across this in some of my notes and can't remember why it was important.
Originally Posted by chief
You guys are causing me to bite my knuckles.
Just some background on me - By profession (for a very long time) I'm a broadcast engineer (I build radio & TV stations) and master electrician in NJ, NH & VT. So I work with this stuff everyday.
I don't own a 100volt machine, only 24 volt units. So not having a power supply to open up and play with, I can only guess the following:
Remember, only assuming! Some power supplies use common-mode rejection transformers. These are center taped. 100V is applied to the outside terminals and the ground is connected to the center tap. We use this system in high quality radio studios. It cancels out the 60 Hz hum that gets into the audio circuits.
If they use this in the machines, you will measure half voltage from the green wire to chassis ground or earth ground. That's normal.
Someone let me know what you find... Unplug the machine and take an Ohm meter (x1 scale) and measure from the green (green/white) wire to some metal parts of the machine. Say, power supply box, rails, etc.
I'm hoping that you will see a dead short. And that's good. If so, grounding to the ground pin on a standard AC outlet is the right thing to do.
But! before you plug it in, do one more test for me. With the power switches on (not plugged in), measure from each plug prong to the same metal parts you measured above. The meter should show open - very high resistance. If it doesn't, there could be a fault or you may be encountering a bleeder circuit (a circuit that drains any charge in the power supply when unplugged) or a surge protector. Some equipment use MOV (metal oxide varistor) that short to ground when there is a spike on the line.
_._ Walt
"This is My Personal Opinion and no others"
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