DMM servos, seeing 90 VAC on the noise filter case

[Accu-Slice]

I have been running the Acorn system using 3 DMM servos for my PM30 mill. I have been using the setup wiring as per DMM and Acorn directions. However, whenever I put a ground to the 1 amp noise filter the system faults. I measured for leaks and other voltages and what I discovered was a 90 VAC voltage between the 1 amp noise filter case and ground. I saw this same AC voltage on the cases of all 3 of the 1 amp noise filters. I do not see this voltage on the first 10 amp noise filter.

I first noticed this issue when I set the system up and clamped the nose filters to the base plate - it did not work since the cases were grounded. So I put a teflon spacer plate under the noise filters. But whenever I attach the ground wire to the 1 amp noise filter the system fails -probably because I as shorting this 90 VAC signal to ground.

Is this 90 VAC leak to the noise filter acceptable or am I getting some feedback from somewhere else?

[Muzzer]

Could do with more info. What supply voltage are you using? Some photos would help. What is this filter?

If you leave the filter ground floating you'd expect the case to measure somewhere between the live and neutral voltages. Neutral is usually near ground potential unless you are running between two 120V live connections in the US.

It's certainly sensible to fit these filters and they need the ground connection to work properly.

[kb58]

Another contributor to seeing high voltages on various parts are high-impedance volt meters, which they all are these days. This means that the meter requires so little energy from what it's measuring that it's nearly an antenna, picking up and displaying even very weak voltages. As an example, just holding the red lead of a volt meter in your hand may show some AC voltage that you and the wires are picking up through the air.

Of course, there could also be a ton of current behind what it's measuring, so you're right to be cautious.

[Muzzer]

EMC filters generally include Y caps between each phase and ground - these are particularly effective for dealing with high frequency common mode noise. These form a capacitive divider, so if the ground connection isn't made, the case will be held between the phase voltages. You don't need a high impedance meter to measure it and you may also be able to literally feel the leakage current if you touch the filter case. But be wary of touching the casing in case there is a misconnection in your system or a fault in the filters (less likely). You could measure the current if you make a connection between the filter casing and ground with a meter - it should be of the order of a few mA, no more.

[cncsnw]

whenever I put a ground to the 1 amp noise filter the system faults.

What exactly does "the system faults" mean?

At first, I interpreted it to mean that you were tripping a supply-side circuit breaker. That would indicate a ground fault (phase-to-case) in the noise filter. But maybe instead you meant something related to the DMM servo amplifiers, or related to the Acorn PLC logic.

What did you really mean?