we have a pump start stop controls going from MSB to PLC panel. We are getting around 140VAC in all cables going to PLC panel. When we measure the voltage between any cable wrt ground its around 140VAC. These control cables and power cables are mixed up in the cable tray. It is for a fibre boat.
What could be the possible reasons.
Do you have shielded cables for the 24 vdc separate from the 140 vac wiring?
Several things are possible.
What is your normal single phase AC voltage? and what is your normal DC control voltage? This will help to answer your question...
If you are running all control cables in the same conduit, then you would expect a lot of induced voltage. Are you measuring this voltage using the cabinet ground as your reference or the actual 24 vdc common? Also is the equipment working?
Measure using the 24vdc common as your reference, and also check it with your meter set on AC to see what level of noise is actually being induced.