I thought they compared the current on the hot to the current on the neutral. They don't need a grounded plug to work. So if the current going in is leaking to ground, say through a person holding a faulty hair dryer in the bathtub, and not back out through the plug it will trip.

 

Just a note, it may be wise to change the GFI plug also, every time they trip they get just a little weaker (takes less to trip it) can get anoying.
If you have some electrical experiance, I would put a regular 20a plug in and change the breaker to a GFI, more expensive, more durable and reliable.

 

You are correct, they trip when there is a difference between hot and neutral of .5 milliamp. And for safety on older homes that do not have ground conductors people install these instead, sometimes it's cheaper than to rewire the house.

For the question of the topic starter. I'd just replace the gfi for starters see if that works. It probably will. If it doesn't work that doesn't necessarily mean your heater is bad either a gfi is not a heater tester lol. You could get an electrician to install a switched single outlet (not the household duplex) which would give you the ability to turn it off before touching the energized cord in the outdoor environment. It would be legal per the NEC and not give you false trips.

 

Thanks for all the replies. Just a bit more info -- it doesn't pop immediately, but rather takes between 10 and 40 seconds before the GFI pops. I have a new GFI plug I can replace the old one with. I'll give that a try. The GFI that's popping is in my basement, but all my garage outlets (3 x 15 amp) are on that circuit.

 

Curtis that is a nice finished look,well done
Dave " dscabra " cabelas and bass pro shops also have em. just fyi

Hanklin

 

Mine was also tripping, pulled the end of the block heater cord and the wires were all corroded inside, replaced the entire cord and no more problem with tripping the plug

 

Didn't I read somewhere that you weren't supposed to use the block heater on a GFI circuit?

 

Mine works fine on it, I'm not stringing a cord inside my house to get around using it either. If I had a garage then I wouldn't worry because it would be heated anyways but no garage yet.

 

BINGO.....its your GFI plug! Krewat is right 95% of the time.

 

Sorry, I can't take credit for that pic. That's someone else's truck. I just stole the picture. My plug is mounted a little higher up on the very side of the bumper..... yes, in the chrome. It actually looks factory the way it's done (at least to me, that's all that counts, right???). LOL

Nah, you can plug it into a GFI without a problem. The problem is in the plug, not the block heater, and not usually the GFI either (although sure, they can go out too).

Most of the plugs in my garage are hooked to a GFI circuit. My block heater is plugged into a GFI outlet. The last time my block heater tripped the GFI was when the plug itself got corroded and was fraying apart. Ever since I chopped it off and installed the Marinco plug, it has never tripped again. This is the 2nd full winter I've had it like this.

The issue with the plug end on the block heater is a very very common problem. Quite frankly, Ford used the cheapest POS they could find. When it gets corroded or starts to fray internally, it will trip the GFI every time. You can get away with it a tad bit longer by plugging it into a non-GFI outlet, but it will eventually trip the breaker anyway as the problem gets worse.

Checking the resistance at the plug takes 5 seconds, and it will tell you right away if you have a problem. If the plug ohm's out fine, then go after the GFI.

 

I work at a Case-IH ag dealership and can tell you that we sell 10 times more power cords than heaters. Pull the cord off and visually inspect it for chaffing and/or melting(read exhaust pipe rubbing), then check it with the multimeter if it looks OK. I'll bet it's the cord not your GFI.

 

Today I pulled the plug from the heater above the starter and tested the resistance. It measured out at 15.5 ohms. I checked the plug - no corrosion. I checked the wiring for any sign of wear, melt, cuts, and cracks -- none found. I coated the plug with dielectric grease and hooked it back up. When I plugged into the wall, I didn’t have any more GFI tripping issues. I think there must have been some water that got into the plug when I pressure washed the truck on Friday. I took the opportunity to secure the wires up and away from anything they could rub against.

Thanks to all for the help,
Dave

 

Old thread revive.

I have a single gfci on the porch, and my garage is also gfci. My 1999 7.3 super-duty diesel block heater will pop the gfci breaker in the plug within 10 seconds.

Nothing else is plugged in either one. I use a good extension cord. I have plugged in various 466I's with same cord in same plugs no issue. My Mercedes 300sd block heater works no issue same cord same plugs. My magnetic block heater works same cord same plugs no issue.

Factory block heater will plug into a normal outlet inside the house with no issue.

Problem I have is when i plug into gfci it pops every time.

Today I even plugged the heater inside for 30 mins to warm it up. plugged it into a gfci and it still popped.

I replaced the end, and ohm test shows no continuity between either flat and round. resistance between flats.

I am going to plug it in the house for a while and see if it is warming. It is very cold (0) right now. Any ideas on how to see if it is working other then trying to start the truck?

 

Feel the block with your hand?

The only reason a GFCI should pop is if it senses any voltage on the ground pin returning from the load. Notice I say "should".

A way to possibly work-around the problem would be to use a 2-to-3 pin adapter and isolate the ground pin. Any hardware store should sell this adapter - it has the two blades on the male end, and all three on the female end. It also has a tab on it that can be screwed down to the center screw on a "normal" outlet, so as to ground the ground pin.

The only thing that comes to mind in this situation is that the block heater has an internal thermostat to keep from overheating, and for whatever reason, sends a surge back on the ground pin.

Are you SURE the gfci outlets are wired with "hot" and "neutral" on the correct sides?

 

I think it is safe to assume that they are wired correctly. House is fairly new and was wired by licensed electrition.

Also, they both work with several other block heaters, as well aspool pump, and air compressor, all kinds of power tools. Nothing else trips it

i have one of those adaptors, I will try it.