When running a 2,3,4…10 hp motor, is gfi the end all for ground fault protection? Isn't the utilization equipment motor energizing the equipment and extension cord long after the panel mounted gfi has tripped? So, it seems to me that gfi protection is of limited value for personal protection. What do you think?
Does anyone know the time vs. amp curve for a partially loaded motor. t=0 would be when power to the motor is interrupted. Would this be less than 6mA in less than 25ms as required by gfi code? Of course this time would be in addition to the gfi protection time to interrupt.
Oops, I guess I should have asked for a time vs. voltage curve. I'd use resistance of the human body to ground to figure out amperage.
For those of us not familiar with motors: motors are also electrical generators. When a motor is turned off, it's doesn't instantly stop, and will generate a current while spinning to a stop. So, if you're not familiar with motors, please don't answer.
Innocent Victim clarified by stating that an unpowered coasting ac motor would continue to generate current only if it were connected to capacitors as the field coils wouldn't be excited otherwise. Sounds good. So the curve would be volts=0 at t>0.
Question answered. Thanks!
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3 responses so far ↓
1 Innocent Victim // Jun 13, 2008
Uhhh, no. Once the GFI trips, then nothing is energizing the equipment and extension cord. GFI breakers are the best addition to home electrical safety systems that ever was.
2 rubber j // Jun 13, 2008
If you consider that 8/4ths of a 72kA capacity is reciprocal to the 14th range of the visible spectrum, then I guess the answer is "Tuscaloosa."
3 Tony Q // Jun 13, 2008
GFI is supposed to protect human electrical shock from touching one hand on equipment casing the other hand touching water pipe, if the current excess 6 ma for 26 ms the GFI will cut off the power. the idea is noble, but is it false sense of security? my answer is yes. unless the GFI is electronics that will cut off the power faster, then i'll have more confidence.
my opinion is when a person soaking wet from taking a bath, the person skin resistance is 1 k ohm, in a 120v outlet, a faulty hair dryer the person may get elctrocuted with 200 ma current by touching the water pipe. the GFI trip at 6 ma 26 ms too slow to cut off the power. and worst, ul #943 spec test is not strict enough, they allow GFI to trip at 6 ma (26 ms to 5600 ms). in that case if the GFI is 6 ma 5600 ms. at that current and time, the person heart will stop and breathing will be paralyzed. probably they tested the product on dry skin (100k ohms) people and claimed its safe.
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