I'm confused, in an earlier post any reading ohm other than zero was a problem and now you say zero is a problem. I did another check and it is definitely 18 V between one and four. Thank you for your patience with helping me with this I'm just getting frustrated because the motor and pump were brand new out of the box a week ago and seems to work fine when wired directly. I was looking forward to cranking up the heater and using it this weekend and now I feel it isn't safe. I can't understand how the gfi isn't tripping if I have a short in the motor.
Sorry if I'm contradicting myself. Thought I was keeping good track of this one.
There should be no connection between any motor lead and the case of the motor. Also, no connection between any motor lead and ground. That equates to an infinite reading on a meter. 0 ohm is a dead short. infinite ohm is an open. There should be some reading between motor leads. 22-30 sounds reasonable.
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On the question of the GFCI. It is possible that it isn't connected correctly. I have one of those for my hottub wiring and it was not installed correctly by the electrician that wired the house. I noticed that the white curly wire wasn't connected to anything. I looked it up on line and fixed it.