I recently wired some operating rooms in a hospital. Each room has an isolation transformer fed panel that is monitored for any ground faults (the milliamps are displayed on two analog and one digital meter). If the milliamps climb too high, the system goes into alarm. In this case, once juice was applied, the system did indeed go into alarm mode. After doing some investigating, it was found that the radio interference filters inside the fluorescent lights were causing the problem. These filters are tied in series with the fixture ballast line wires. With the filter bypassed and only the ballast hooked up, everything was fine and the monitor read no loss of current.
We have not been able to get a hold of the electrical engineer on this project yet so I thought I'd do some investigating of my own (that’s where my fellow forum users come in). Do these radio interference filters send a small amount of current to ground while performing their duties? If so, they obviously should not have been spec'd for this application. Is there a higher-end filter that would not cause the problems I'm experiencing? I could probably isolate the metal case of the filter from the fluorescent fixture but that may negate or decrease the effects of the filter and probably would not be safe or UL approved. There would be no place for heat or current to dissipate and the fixture would be modified from its UL approved set-up.
I'll probably have an answer back from the engineer by early next week but my curiosity is building!
