I have two five-year-old 16 mm x 428 mm, 115 VAC, 1000 W cartridge heaters that have approximately 200 kΩ from the heater leads to the exterior stainless steel sheath. Is this normal or should I expect more isolation in newer cartridge heaters? I am asking this question because I have a reaction heating block with the above cartridge heaters installed and upon turning the controller up to any above-ambient temperature (e.g. 60 °C), the 20 Amp GFCI outlet breaker trips. If I plug the same unit into a non-GFCI 20 Amp outlet, the unit heats up correctly without tripping the circuit breaker covering the room. The GFCI outlet was recently replaced and yet we still have this issue. I had noted a ~200 kΩ resistance between the ground and the heater leads and then extracted the heater cartridges and made the above observation on the cartridge itself.
I was dealing with exactly the same issue few years back. The equipment we were designing and manufacturing wasn't passing final safety inspection for similar reasons. The recommendation of the vendor was to let the heater rods dry-out by having them exposed ho high temperature for an extended period. That didn't solve the issue and we ended changing vendors.
How such seemingly simple device can complicate life, right?