However, GFCIs are not perfect. The Water Pik that I use for washing fungus colonies out of the inside of my nose ( using a homemade tool ) sometimes nuisance trips the GFCI when I turn the Water Pik on of off. Since the tool is inside my nose when this happens and I do not feel a shock, there must be some type of static electricity phenomenon or a nonlinearity in the current transformer for sensing faults that must be causing this.

I still feel that GFCI is a great safety device. I one time applied Leviton's high current GFCI to a 480 volt 3 HP motor and a 10 KW single phase heater that were on 277Y480 volts. This was a chemical tank into which the operator was pouring in rust inhibitor and filling it with a hose. I also put in a current relay to check to see if the electric heater was actually delivering heat to the tank to also protect the customer.

Yet, there are some appliances that cannot be GFCI protected using the more common devices. Older refrigerators have too much normal leakage current which is not a hazard IF the appliance is grounded. Same for engine block heaters on diesel trucks because salt water forces its way into the wiring. This is not a hazard IF the truck is grounded. Similarly, if you do not ground the hoist motor of a 480 volt bridge crane the hoist ropes will have a nasty tingle voltage because of wiring capacitance to the frame no matter how ggod the motor insulation is.

The coal mining interests developed a technology just for these kinds of appliances and as a result the British have not had an electrocution in their coal mines since 1963 and they have 1,100 volt and 3,300 volt extension cords. What they use is continuous monitoring of the equipment grounding path so that the GFCI can be set to tolerate normal leakage current of an 1,100 volt motor. They also use resistance grounding of the power source so that ground faults are nonincendive and can be located and removed by the electricians. They also use individual shielding of extension cord conductors even for 110 volt hand tools so that if a wire strand breaks and then works its way through the insulation it will trip the GFCI before it reaches the surface or another hot conductor. About the only time that they have an electrical fire is when a machine runs over its own cord which happens about once in 10 years.

If go into say a U.S., coal mine 120 volt tools have 4 prongs, 2 for 120 volts, 1 equipment ground, and 1 ground check. This provides 24/7 assured equipment grounding anytime something is plugged in.

Essentially, there is such a thing as a 3,300 volt or 4,160 volt extension cord that is as safe as breakfast food.