GFI breakers are not recommended for kilns.http://www.hotkilns.com/what-gfci-or-gf ... ctric-kiln
Q: What is a GFCI or GFI Breaker or Outlet AND Why might it trip when used with an electric kiln?
What Is A GFCI Or A GFI Breaker Or Outlet?
A 'GFCI' or Ground Fault Circuit Interrupter, sometimes called a 'GFI' or Ground Fault Interrupter is part of either an outlet or a circuit breaker.
It is typically required for added safety on any circuit that may come in contact with water, like outdoors, or kitchen, or bathroom.
A GFCI measures the amperage on both the hot and the neutral wires in a 120 volt circuit, or it measures amperage on both hot wires in a 240 volt circuit.
If there is more than about a 5 milliamp difference (5 thousandths of an amp difference) between the amperage readings of the wires the GFCI acts like a circuit breaker and shuts the power off.
Why Might It Trip When Used With An Electric Kiln?
In a kiln, the firebrick is not a perfect insulator, so a tiny bit of the current leaks from the elements to the safety ground and unbalances the current in the 2 hot wires.
The resistance of the brick goes down as the temperature goes up so the kiln may be able to start a firing and but the GFCI would probably trip as the temperature went up.
Above 1700 F is when the firebrick has a significant drop in resistance.
Due to the nature of the firebrick in a kiln, GFCI protected circuits are not recommended for use with the power circuits in electric kilns without special element insulators.