GFI problems
GFI problems
(OP)
I am retired from the power transformer testing department of a southeastern utility...I had a problem that I never got to investigate throughly. When testing transformers with LTC's (Load Tap Changers), whenever I would apply electrical power to the controls, out safety department required that we use short pigtails with GFI protection. Whenever I would energize the control, it would kick the GFI out...the only way I could test these controls was to by-pass the GFI protection. Not all but approximately 95% of the controls required this. I even devised a test scheme and simutaneously measured the current in the hot and ground wires. The best I can remember, there was a difference of approximately 40 - 60 miliamps...which is more than enough to activate the GFI protection device. What I never did find was why that much difference?






RE: GFI problems
RE: GFI problems
RE: GFI problems
RE: GFI problems
GF protectors are available in various models. By GFI one usually means a device for personnel protection. Like stevenal says, these devices trip under grounded neutral conditions (even if there is no load), as well as grounded hot line. The reason for this is that people could suffer hazardous shocks if they serve as ground paths for either one of the hot or neutral wires. Also, the trip levels for personnel protectors are usually lower (5mA in USA, 10mA in Europe).
There are GF products rated for equipment protection. These products have no grounded neutral protection, and the range of trip levels varies according to applications and manufacturer's specs.
RE: GFI problems
RE: GFI problems
http://www.allanson.com/tech_support/sgfpart.pdf
etc. for more info
RE: GFI problems
I think you have the answear there. Capacitive coupling
between the device under test and a grounded metal test
table could cause the unbalenced current in the GFI.
Particularly if switched on when the sine was at the peak.
Or is there internal to the control a static bleed off
resistor to frame.
Rodar
RE: GFI problems
http://www.ecmweb.com/ar/electric_gfci_basics/
for: GFCI basics
http://www.ecmweb.com/ar/electric_code_basics_3/
for: NEC Code GFCI requirements
http://www.unitedpower.com/safehome.htm
for: GFCI safety
etc. for more info