Join Date: Apr 2000
Location: Sedro-Woolley, WA
Feedback Score: 0 reviews
Re: Why did my Block heater start tripping the GFCI?
My block heater does not trip my GFCI.
A GFCI outlet compares the current going into the "hot" prong to the current coming out of the "neutral" prong and if there is more than a 5 milliamp difference then it trips the outlet because it is assuming the lost current is going somewhere it shouldn't (like your body). It is there to protect humans not equipment.
Anyway, you should have continuity between the "hot" and "neutral" prongs on the plug of the block heater (the two flat blades). However, it should not read 0 resistance...there needs to be some resistance in there which is the heating element (my truck isn't here so I can't measure but it's should be around 10 ohms). There should not be continuity to "ground" from either the "hot" or "neutral" prongs but there should be continuity to the truck from "ground".
So, bottom line: you are leaking AC current from your block heater into your truck. Try plugging the block heater into another outlet and then measure AC voltage between the coolant (in the rad filler neck) and the engine block...see what you get.
1985 F250XL, 6.9L, C6, 4x4 (BW1345), Dana 44HD front, Dana 70 LS 3.54 rear, 190,000 miles, Rebuilt longblock (88,000 miles), ARP studs, electric fuel pump, Edelbrock Performer IAS shocks, Velvet-Ride Shackles, Firestone Airbags all around, Transfer Flow fillnecks, lots of gauges, Line-X, Jordon Brake Controller, B&M Stacked Plate Transmission Cooler, TCI Aluminum Transmission Pan, Banks Sidewinder (wastegated)