I just installed an 03-04 great lakes sunlighter I got from my sis and bro-in-law. I'm using the same gfci and box he used which is 50A, 220V. When I turned the tub on it tripped the GFCI. I disconnected the heater contacts and the tripping stopped so I am pretty sure the heating system is at fault. I figure the resistance through the coil should be more than 8.8 ohms w/ the 25A fuse and 220V. Mine reads 11 ohms and a forum post mentioned 9-14 ohms is a good range. There is also no continuity from either heater post to ground. So is the coil or circuitry at fault? If the heating coil is the problem how is this so when it checks out w/ my multimeter? I also noticed that w/ power disconnected there is no continuity from the incoming red terminal but the incoming black reads about 45 ohms to ground. Is this normal? I've got some engineering background and familiar with some ciruitry but w/o a schematic I'm all thumbs. Got any hints to help me understand this system?
Thanks
Pat

45 ohms to ground, no bueno. disonnect that lead and see what you get from that terminal to ground, then that black wire to ground.

any less resistance to ground than about 5M ohms is no good and will trip a gfci