Two pole 30 GFI Tripping

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Hawkeyec16

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Laramie, Wyoming
Hello All,

I have some Heat trace that is tied two pole 30 amp GFI breaker 208Volts. one leg goes through a contactor that is controlled by a temperature sensor. when the sensor opens the contactor the GFI trips within 30 seconds. there are 6 other circuits with the exact same setup that do not trip. I have put the system into "Hand" Control and the GFI does not trip unless the test button is pressed. I have left it in "hand" for 5 months with no trips. I have checked all connections and haven't found anything that would cause this that I could see. I have been scratching my head on this one and I am sure the issue is right in front of me but I cant seem to see it on this one.:?
 
You appear to have symmetric leakage (either capacitive or resistive) between the heat tape and grounded metal.
When the heat tape is connected to both line poles the average voltage between it and ground is only 120V, with leakage current corresponding to that voltage.
When only one pole is opened the average voltage to ground becomes 208V.
That can increase the current drawn to above the trip threshold of the GFCI.
If you instead open both line connections the voltage will be zero and there should be no current.
Switch to a double pole contactor or use a GFCI with a higher trip current.
 
thank you,
I will look into a higher trip current GFCI, since these are dedicated hardwired Heat trace circuits. I will also look at getting a new contactor. the contactor will be harder to change. These heat trace circuits are on 3 pole contactors and one leg of each 2 pole breaker is controlled by the contactors. They are enclosed in a 16x16 inch Nema enclosure and there isn't much room left inside.
 
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