Issues with 480 volt retrofit led pole lamps.

H

HertzGood85

Member
Location
California
I recently installed (40) retrofit pole lamps fixtures on existing 22' parking lot poles. They have replaced the older 400 watt HID style lamps. The issue I am having is that when I did a shop test on the retrofit lights to check them out for issues before installing them, I found when they were energized if I disconnected the ground wire the whole can was energized with 120 volts ac. When I reconnected the ground wire to the two led drivers the 120 volts disappeared. The voltage setup that these pole lamps use are 2 legs of a 480 volts wye connected system. So basically, two hots and a ground. Has anybody come across this issue or does anyone understand why a 480-volt 2 leg system would displace 120 volts to the casing of the lamp when the ground is removed? Thank you.
 
HertzGood85 said:
My meter lead was on the inside metal housing and the other lead was too a grounding bus in a 480 volt panel.
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But was it an ordinary DMM (high impedance) or was it one with a low impedance setting for voltage testing?

By disconnecting the EGC you present a great opportunity for capacitively coupled voltage to show up on metallic closures for those conductors, but the so called capacitor is a pretty weak one and it doesn't take much to "short it out" but it takes lower resistance than most typicall DMM's have and that is why they will register a voltage reading.
 
Try measuring this voltage with a solenoid meter or with a 120V lamp in parallel with your high impedance meter

If the 120V goes away, that is evidence for the capacitive coupling or normal insulation leakage described above. If the low impedance test eliminates this phantom voltage, then you pretty much don't have a problem.

If the 120V stays with a low impedance measurement, that indicates a real problem.

There is a grey area where you might have more than allowed leakage current but still small.
 
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