120V surge when troffer is switched

[keithinvally]

I have a friend who was a physical therapy office. He told me a electrostimulas machine plugged into a receptacle was shocking his patients when the 2x4 fluorescent troffer in the room was turned off. I checked voltage with my digital and found that the voltage varied from 120 to 174 volts when the light was turned off. The service at the office is a 200A- 120/240 volts. The receptacles and light are all on the same circuit. Also this is an older machine, when a newer one is plugged in they do not experience the problem. What do I tell him is causing the problem. He is the kind of person who wants an answer. Please help.

 

[highkvoltage]

Re: 120V surge when troffer is switched

keith. Is the troffer fixture an older style that uses a starter? If so about 10 years ago I had a simular problem. Someone wired the neutral at the light to be the switched leg. Since the starter acts as a capacitor it was discharging though the ground. It all I could come up with. This was in a denist office and the chair sat on a rubber ring. At times when someone touch the chair they got shocked when the light was off, but not all the time. I think that depended on the type of soles on their shoes. I changed the fixture and changed the wiring to the switch and it worked.

 

[keithinvally]

Re: 120V surge when troffer is switched

No, the fixture is fairly new(within 5-7 years or so). I thought it had something to do with harmonic distortion, although I'm not that up to snuff about it, I've heard of it, but I don't really understand it.

 

[bennie]

Re: 120V surge when troffer is switched

The stimulus machine should be on a dedicated redundant ground circuit. I suggest hospital grade receptacles be installed.

The pads, on the skin, are seeing the voltage spike, and passing it through the patient.

There is a possibility of serious injury to a patient.

 

[dereckbc]

Re: 120V surge when troffer is switched

Originally posted by keithinvally:
I checked voltage with my digital and found that the voltage varied from 120 to 174 volts when the light was turned off.

Roger, you got your ears on. Here is your first clue. Start by checking the neutral cicuit at the service. Sounds like a neutral is opening up. Your voltage should not vary that much.

Hospitals and patient care areas are not my field, but patient care areas require special circuits, and redundant grounding. Maybe Roger or someone else can help here.

Forget the harmonic issue, waist of time.