I'll bet they didn't check for leakage with a "megger" (high voltage megohmmeter). They probably just ohmed the elements to see if they were "open".
What I'm concerned about is that your GFCI tripped when you had the mounting bracket tied to ground.
Unless you had something connected wrong when you did that test, the GFCI saw leakage current within the element.
When you later tried that same element mounted in the smoker, did you have its mounting bracket electrically connected to the frame of the smoker?
If so, was the smoker grounded, too?
Because if the heating element's bracket was electrically connected to the smoker chassis, and the smoker chassis was connected to ground, then the same thing should have happened (the GFCI should have tripped).
So my concern is that the GFCI didn't trip, but it should have. So I think something wasn't properly connected when you had the element in the smoker.
I hope that makes sense.
Edit To Add:
I need to stop reading and especially posting to this forum from my phone. I did not see a number of posts that took place above this post before making this post.
It looks like
JC in GB
already covered a lot of this very well.
I agree that if the mineral insulation in the heating element absorbs moisture, that could create a leakage situation. And because heating the element may well drive enough moisture out of the element's insulation to lower or eliminate that leakage, I can imagine a scenario where the first test-heating of the element drove out enough moisture that when it was later installed in the smoker, it was dry enough to be safe, and no longer trip the GFCI.
I'd still make sure that the element's bracket is grounded to the smoker, and the smoker is grounded properly. But if, with things properly assembled, the element doesn't trip your GFCI, then everything may be just fine.
If it was me, I'd reassemble things and then measure the resistance from the sheath of the heating element to the ground pin of the smoker's ground pin. That resistance should be very low. Ideally, below one ohm.
If you've got good continuity from the heating element sheath through to the ground pin of the smoker's power cord, then you should be good to go. And if the system doesn't trip your GFCI, then that's excellent!
