Block heater

[Derkperk]

Hey guys. I've been having issues with my block heater tripping my gfi on my garage outlet. I've switched cords and circuits without a change. Wondering if one of you can check the resistance of your heaters to compare with mine. I get 14.9 ohms when it's cold. Any other input would be appreciated.

[MikeL46]

That sounds about right for a 1000W heater.

Mike

[rforsythe]

*Any* moisture will trip the GFCI. Condensation/dew from the atmosphere has done it for me. One trick is I tuck the cord back into the cavity after plugging it in, this keeps any nighttime precip from getting in there and seems to help with condensation/frost for whatever reason.

This drove me nuts for a while, but just not leaving the connection hanging out in the breeze generally works for me.

[mattspersic@gmail.com]

You might have a pinhole sized breech in the insulation. Usually resistance won't cause a ground-fault GFIC trip (low resistance will trip on overcurrent). I've found the breech is usually at the cord grip (where it mates to the molded plug or heater body). If it is an old heater, there might be moisture or leakage inside (i.e. current leakage from element to fluid or exposed to interior moisture to metal case). A simple Ohm measurement won't detect this (you could use a Megger or 1000 V insulation tester *but* I'm not sure megging-it on the vehicle is a good idea ... I know the ECM/ECU won't like being nearby! and you might fry an I/O port.)

If it is an old GFIC breaker, the breaker could be bad (even a new one) - I've replaced a few in my job. Things like old drills can sometimes get a flakey GFIC to trip. You might check the torque on the GFIC breaker terminals - if the GFIC trips after a few minutes or more, loose terminals might be causing heating of the breaker and it will trip. Our customers check screw terminals annually with a FLIR thermal imaging unit (just tightening is no longer recommended because you over torque and stress the metal year after year).

Try an extension cord through a window to a known good bathroom or Kitchen GFIC outlet or another GFIC circuit. If it doesn't trip, I'd replace the breaker. It could also be the wiring from that GFIC breaker - especially look for a poorly bonded neutral (white) or ground wire in EVERY junction box. Poorly bonded hots (black) generally don't cause ground faults. Make sure that someone didn't add a GFIC outlet on the same circuit with the GFIC breaker (you can't use the two together).

Good Luck. Let us know what you find.

[Derkperk]

Hey thanks guys. I have tried different circuits and different cords. I thought about megging it but wasn't sure about the trucks electronics.
Both gfi outlets trip nearly instantly. I always keep the plug covered and stuck back behind the bumper when not in use. What does it take to remove the heater? Is there a c clip or snap ring that holds it in? I'll try and pull it this weekend.

[Derkperk]

The moisture thing brings up a good point. We recently moved and I am now parking the truck in detactched, unheated, dirt floor barn. Oh, it's killing me, I know! The dang dirt floor keeps everything so damp in there. I'll put the truck out for the weekend and recheck. Thanks guys.

[ritschner]

You can buy a good 20 amp HD Leviton outlet for $5. If you think GFI,s are troublesome, try Arc-fault breakers.

[Derkperk]

I don't have arc faults in the house, thank god, I have heard they can be a bee-atch. Swapping the gfi may be an option...

[mattspersic@gmail.com]

If you have a blank slot in your circuit breaker panel, it would be quick and easy to just add another breaker (non-GFIC) and run a piece of conduit out to the barn (I think you said it was a barn or dirt floor structure) with a outlet... maybe even branch off and add one at the end of the driveway. It might not meet your local electrical codes, so you may have to remove it if you ever want to sell the house. If you do add a new breaker, pick a leg opposite to some load that will be operating at the same time (i.e.: if the truck is plugged in at night, use the opposite leg that something else that runs at night is on, like a heat tape, refrig, et cetera). You could also get a cheap old Intermatic pool timer and wire it in so you don't heat the truck all night and it just goes on at 3 a.m. before work. I'm looking at building a house this summer and I am absolutely putting outlets under the eves for Christmas lighting and heat tape and at the end of the driveway for the truck and motorhome. I think those are the important things that builders so put in homes. Sorry, I digressed. Good luck.