AC plug wires are reversed and Above ground potential

I don't believe it's possible to test for all potential faults by any method. If the equipment you're working on is as bad as that, use the isolating transformer - it's a lifesaver.

 

A ground potential above zero volts sounds symptomatic of a floating ground to me. Are there schematics for the equipment and can you open up them up and and inspect them?

 

I don't know what the heck is going on here, but I'll submit my two-cents worth.
1) When electricians wire power outlets, they drop the 480VAC three-phase from the outside power line, into three 120VAC single-phase lines. (If you're in the U.S.)
It's called 'balancing the load', of turning one 480V 3-Phase line, distributing it into 3 each 120VAC lines for use.
If you run power from one input line to equipment, and then tie that equipment into somthing that's drawing power from one of the other original 3-phase input lines, you're 'cross-phasing'.
That means your 'neutral' at your euipment, could be seeing it's neutral tied to 240VAC, the 'hot' wire from one of those other original 3-phase input power lines.
Is that what's happening here? Or are we looking at something else going on?
2) My other thought here, is that there are plenty of circut voltage testers on the market to check power outlet voltages. Are you just using electronc test and measurement equipment here,
or do you have access to basic electrician's test equipment?

 

Not sure what is going on either.
If we are talking about a single phase 120v plug (cord cap) there is technically no neutral. There is a hot, grounded, and when it's 3 prong plug; an equipment ground that hooks to the grounding pin.

You should have a polarized plug with the grounded pin (neutral) physically wider than the hot.

You should use an ohmmeter on the cord cap (plug) to verify infinite resistance between hot (non polarized skinny pin) and the chassis.
On old equipment, they would bond a chassis to the grounded (neutral) conductor, but this is not safe, primarily for anything metallic because the grounded conductor carries current.
The chassis should be bonded to the grounding pin (equipment ground) conductor only.

 

I think it might be time to ask an electrician for help.

 

I am an electrician

 

Sorry, I mean an electrician right there, to clear what might be a potentially lethal fault.
The OP is in another country, isn't he?

 

I hear you, it's better to understand something in front of you, rather than going on basic descriptions on a forum.

If we knew more about this "equipment" perhaps we could be of help.
In the meantime, cut off the plug so no one plugs in this dangerous thing.