Get somebody with a battery operated (to avoid just another ground issue) oscilloscope to probe the various sections of your wiring in a systematic fashion. Once you "see" the noise (including frequencies and amplitudes) you have a handle to test changes immediately. Otherwise you may just continue the hit-and-miss experimentation. There must be something unique about your setup so that the standard recipes don't work. Right now you don't even know if this is high frequency noise (like from VFDs), if it is radiated or conducted, or if this is just AC leakage.
I rigged up a long wire lead to one of the probes of the multimeter and checked continuity, which exists from the bare copper wire at the dust show all the way to the ground bus on the electrical panel. I don’t know enough to determine whether the continuity is “good” or however you’d measure it, but the multimeter beeps. Sometimes it’s a bit of a staccato beep. But it beeps.
Also grounded the frame.
Any ideas?
Try it with the grounded frame and report back!
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It seems the DC is the culprit. As some have mentioned, it is completely possible for the motor to have a goofy winding in it that causes electrical noise. Static is generally a problem in the dead of winter when the air is really dry. It's probably plenty humid where you are being so close to the lake and with the number of storms that have passed your way recently. Did you have this same issue during mid summer?
As a means to an end, I think only a professional motor repair guy would have the know how and equipment to find out if the DC motor is wonky or not. The manufacturer probably doesn't have a clue about static other than making sure their electrical and chassis grounds are terminated at a common point.
The other thing that *may* cure the problem is some kind of line conditioner that will clean up the electrical signal. Electrical noise & conditioners are very common in manufacturing...there can be noise issues with spindles, DCs, pumps, hi-freq welders and plasma cutters...and not to mention your electric service itself can be noisy as well. Without an O'scope you have to play the guessing game.
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"It's much dryer" how about a hot plate and a pot of water to raise the moisture/humidity inside the shop? Where my shop is located is high mountain desert and when its dry its dry! I wish you well on your quest! Russ
AKA: Da Train Guy