Block heaters trip GCFI?

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  • #758421
    Madrid, NY

    I’ve been out of the trades for a while.

    We had the roof at work collapse back Feb, resulting in a 2 month layoff for me. Upon being called back, one of the things I noticed hadn’t been dealt with was outlets that the roof coming down destroyed that we rely on to plug in a old truck we only use on the property to haul trash from our building to the transfer station. Very cold blooded and needs to be plugged in below 60F or it wont start.

    Management thought the electrician was going to replace the outlets, but when I talked to him he had no idea, which resulted in additional work for him.

    Late last week, he asked me if we needed GFCI inside(he wasn’t planning on putting GFCI on the exterior outlet, which is back to back with one of the interiors, as the block heater in the truck would trip it. Circuit has (3) duplex 20A outlets, on what I’m guessing is a 20A circuit. Electrician said (2) block heaters would trip the breaker. I can’t see a block heater using more than 1200w, so not sure why it’d trip(I haven’t taken a close look at the internal block heaters, so unsure of wattage. Management insisted on GFCI for the exterior, but not the interior.

    I’ve had mixed results in the past, so unsure how true the “block heater will trip GFCI” is. I know the block heater on semi truck we have will trip a GFCI, the skidsteer will not. Unsure on our little trash truck, as I can’t recall if the outside outlet was GFCI protected or not, and the wall it was mounted on went away with the repairs, making space for a yet to be installed larger door. We had thought the semi truck had a block heater wiring problem, but our shop said nothing was wrong with it.

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    Montreal, QC

    GFCI shouldn’t be tripped unless block heater is leaking current to ground, it isn’t going to tripped by high current.

    A quick google search shows block heater can go higher than 1200w so I suppose if you plug two of those in it’ll trip the breaker. Besides breakers are only rate for 80% continuous load so your 20A breaker can only supply 1920w for extended period of time.

    Fort Lauderdale, Florida

    Is it tripping the GFCI receptacle directly or is it tripping when plugged into a regular receptacle wired to the load side of an “upstream GFCI” receptacle?

    GFCI seems to be sensitive to certain appliances. For example many refrigerators, have inductive loads that when switched off, produced EMI which can trip GFCIs. Don’t know if that may be the case with your block heaters.

    I had refrigerators that would occasionally trip a GFCI, or a receptacle wired to the load side of one, and once I rewired it from the line side, no more issue.

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