As mentioned before, I had the exact same problem you experienced and the problem ended being mag chloride and road salts built up on my block heater chord connections; leading to current leakage. Once I cleaned those up, and sealed them to prevent future exposoure, my block heater is working fine in my GFI outlet -

Mark;

I haven't had a chance to check into that yet, but I don't think that it is the problem. The truck is still new (only about 1,500 miles on it) and we had such non-winter so far, it has had very little salt exposure, so I don't think that it would be a build up of that as the cause of the problem.

Thanks.

 

Duh! Time to buy a little larger extension cord.

 

I have found a solution that works for me. This goes without saying, but it's a "at your own risk" type of thing, and you need to know what you are doing when messing around with outlets in your house.

I simply went down to Home Depot and picked up a 20A GFCI outlet to replace the 15A one that keeps tripping. Swapped it out and it hasn't tripped again. So now I still have a GFCI outlet, and it's not constantly tripping. The old one was so bad that I couldn't even run any power tools in my garage off that outlet.

Anyway, that's my 2 cents.

 

Alright, a GFI is not an overcurrent device such as a circuit breaker. It is National Electrical Code requirement for a GFI to trip if the amount of current between the Neutral (grounding electrode conductor{white wire}) and Ground (grounded conductor) exceeds 3 - 5 milliamps. The cause is most likely the block heater if the extension cord has been replaced already and power tools work just fine in the recept. Check for any type of mark on the heater cord such as a cut or scrape. Take a multimeter and test the heater plug, left blade to ground. You must have an open reading.

 

ya 20 yr electrician you are probably overloading the circuit

 

This is the exact reason I tell people NOT to plug a deep freezer into a random outlet in the garage, if it's a newer home. Chances are that outlet is GFI protected and if it kicks for some random reason, you'll be throwin out some rotton mean. Pull a dedicated circuit and put in an outlet just for that.