After further thinking on this, and Tim's very good post I might add, there is a possibility that the element could be doing a slight short to ground and not trip the fuse. So I'll retract my last post as yes, now I can see Tim's point. Learn something new every day. I'll go back and edit it.
Let me explain my thinking or try to. The element is fixed resistor for all practical purposes running on AC.
The neutral wire of the new element is separate from the normal ground but is tied to earth ground at 1 place in the power panel, so it is common to ground by a continuity check. So far so good.
The power hot wire is separate from ground and it is tied to the other wire of the 2 wire element. The GFI is sensing any current flow between the hot and ground.
Again so far so good.
As Tim pointed out and started my thinking...
If the slight short to ground in the sheath is very close to the hot wire infeed, well that portion of the element will develop sort of a voltage divider network and that path to ground may actually trip the fuse.
BUT
If the path to ground ends up on the AC neutral end of the element, well in the eyes of the fuse, the system is still seeing almost 44 ohms to AC common. It may not then blow the fuse but will developed a current path on the ground circuit and trip the GFI.
Pending where in the length of the element the short took place, will determine a fuse blow or not. And since there is no polarity on the leads, again pending where the short is, switching the leads may actual blow the fuse if the short is close to one end. If it is in the middle, well maybe/maybe not.
Tim's point about moisture fits and obviously comes from seeing this before. I never thought of that but can see the light now. :S
If you really want to test the theory, with the unit unplugged and the element disconnected and cold, do a ohm meter check on each wire lead of the new element to case ground. There should not be any notable resistance there at all. It there is then it has a leak from the start and it get's worse with temperature.
If is OK cold, put the unit together, heat it up. When it trips, pull the plug, unhook the leads and then check the path to ground again. If it is leaking, you will find some path to ground tripping the GFI.
The thought on the amp probe was:
If it starts out pulling x amps cold and then when it heats up, if it start pulling more current, well the unit is shorting inside as it is pulling more current. In a resistor setup, some part of the resistor found a short cut to ground and thus it will pull more current. May or may not be enough to trip the fuse.
Basically you created a mini voltage divider network. Think of it like a normal potentiometer, 2 leads of the coil created a fixed voltage/current drop. The 3rd wire, the sweep, now creates a new load. The short or moisture drop is the sweep lead creating more current on the upstream power feed wire.
I might add, you have created a real good electronics 101 experiment here.
Please let us know how you make out.
John
