Completely agree!

Steve

 

Last I checked, this only happens with DC systems. The block heater is using AC. Agree with others where it is unlikely that this is causing the GFCI to trip.

As noted, the most likely explanation is that some current is escaping from the system and going elsewhere (not returning back to the outlet). Once the electricity leaves the wiring, it will want to return 'home' which is probably the closest electrical transformer and anybody in the path (however the current decides to get there (which is not always a straight path)) is at risk. The GFCI is tripping as it senses the issue and is doing its job of preventing somebody from getting a shock.

Probably a good idea to get a setup that does not trip the GFCI as, if the electrical leak is in the truck somewhere, aside from a possible shock hazard, it might lead to corrosion depending on where the leak is occurring. Search on stray current electrolysis for more details.

For reference, one of my block heaters continually tripped the GFCI but would work on a standard outlet. The cord and element were clearly recently replaced by the PO when I bought the truck. A new heater element cured the GFCI's tripping.

 

What do you mean by "undersized GFCI"?

 

Using a 15A GFCI when a 20A or larger would be needed. In this case it should be a 20A circuit with a 20GFCI

 

1 GFCI is bad
2 Salt, water, rust, crud on cord end or the heater on the block
3 your heater is faulty, need a meter to measure resistance on all three terminals


I tripped my GFCI once and my extension cord to camper was in a puddle, son moved it to use his go cart

 

Why would they need a 20A circuit?

Per the code, you can load a circuit up 80%, 80% of a 15A circuit is 12A, which has more than enough capacity to power the less than 8.5A these block heater pull......

 

I don't see why that would make a difference, GFCI receptacles are not over current protection devices, a 15 amp GFCI will happily deliver more than 15 amps till it melts if there is no ground fault.

I agree it's always nice to have a 20 amp circuit but the block heater only uses about 8, so even sizing the circuit at 125% (which isn't even required) a 15 amp circuit would suffice if it were not loaded down with other things.

Some argument could be made that a dedicated 15 amp circuit would be better as it would protect the 13 and 15 amp extension cords that most people use.

 

You are correct on the loading of a circuit. I recommend 20A circuits for garage outlets even if not required by code because of the typical loads put on them. For specific code requirements, I would need to know more about the whole setting. Age when built, detached or attached garage, etc. For example, frequently detached garages have a single circuit run to them. People add in drill chargers, garage door openers, exterior and interior lighting, etc.

There are some code requirements that do require that circuit in certain circumstances. There are circuits recommended above code requirements based on experience of normal usage.

 

I had the same issue, block heater tripped my GFCI, but only when things were wet (think rain or freezing rain then temps fall well below freezing)

Would not kick out normal 15 AMP breaker, just the GFCI.

Found out my cord was no good, was pinched sort of between the fender well and frame, bare wire.

I put a new cord on, no issues with 15 AMP GFCI kicking out again.

Replace cord before cord causes replacement of truck.....

 

In the third post he said one was ordered. I'd say lets see what happens after it's replaced.

 

But this is not how you stated it in your post.....

The way your post read, he would have to have a 20A circuit and GFCI installed for his block heater.

I was trying to save the OP some worry and potential spending of unnecessary funds to fix a non-issue.

 

Hey sometimes the info online is worth what you pay for it! I'm to the electrician. He has it right, the GFI senses an imbalance in the Hot and neural lines. I am not sure how well they work without grounds. Your issue is most likely leakage current. My background is in electronics. The block heater is a restive device. Longer power cords, or small gauge wire will result in less power delivered to the heater and lower power consumption. The I^2R losses in the cable will result is lower voltage at the heater. OK
Something is wet, contaminated, or the insulation failing. It's not the cord or and its likely not the GFI. You can likely measure it with your ohm meter.

 

I've been doing some reading on this and Karlow nailed how the GFI works and what will actually trip it.... Now that I'm a "self taught Internet expert" on GFI's, what dose the GFI do if you plug in a known good electrical load of similar amperage?.... GFI's do occasionally go bad apparently, it would be a cheep way to test it but the advice above my post is most likely your issue.

 

Happily delivering current until something melts is the exact reason for the code to begin with.

While I did not state my advice on a larger circuit was based on usage patterns over what code requires, it does not change my advice.
For the same reason that a 14g extension cord is rated at 15a and could carry the load, but many, including myself, recommend a 12g. It is for safety and long term use.

 

No need to over think this one! The solution should be quite easy to achieve due to the simplistic nature of the components involved.

Happy Holidays!