Good Evening,

We have a customer we installed a UPS and generator system for around 2 years ago. While completing some maintenance earlier this year, one of the on site maintenance team alerted me to a potential hazard.

The steel battery frame is painted/coated, but there was a nick in the coating, someone had leaned on the frame, at the location of the nick, leant on an earthed panel besides them, and had a shock.

All that is on the frame is the batteries, but we measured an AC voltage of around 170V between the frame and earth.

Above the frame are the main incoming cables from the transformer which is 2MVA - 3No per phase 500mm, I think they are AWA but cannot be certain (the site is 400 miles away so I cannot easily check).

There doesn't appear to be any cables touching the frame.

Any ideas where the voltage might be coming from, the phases are pretty well balanced - could an induced magnetic flux cause the frame to act as transformer? 

We are due to complete more maintenance next week, we will be running the site on generator, the incoming cables will still have the same voltage (LV - 230V L-N), but there will be no current in them, I have someone on site who will check to see if theres a potential on the stand at this time. Is there anything else you would recommend checking?

Thanks, Shaun