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Thread: GFCI for Engine block heaters

  1. #1
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    GFCI for Engine block heaters

    I have a situation in a parking lot of a government facility that utilizes cord connected engine block heaters to its vehicles that remain outside. They are currently on GFCI receptacles as per 210.8 (B) (4).Extension cords are commonly used to reach the vehicles. The problem is that we are experiencing a lot of tripped receptacles during the overnight hours and come morning, the engines don't like to start because of the extreme cold. Now, the wording in 210.8 (B) (4) states accessible to the public as part of the requirement. Are employees considered the public or could we remove the GFCI protection and eliminate the nuisance trips? The vehicles are in a secure, fenced in area. Any thoughts?

    [ December 19, 2005, 02:22 PM: Message edited by: m73214 ]
    Tom

    " And all the science I don't understand, it's just my job five days a week "

  2. #2
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    Re: GFCI for Engine block heaters

    What about installing new conduit to the location and supplying a few receptacle in the fenced off area.

    Reading the section, it would seem that if people working there move about the area, it may be considered a public space.

  3. #3
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    Re: GFCI for Engine block heaters

    The problem is that the whole parking lot contains about 50 vehicles and that is the fenced in area. They all have the block heaters installed.

    [ December 19, 2005, 02:41 PM: Message edited by: m73214 ]
    Tom

    " And all the science I don't understand, it's just my job five days a week "

  4. #4
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    Re: GFCI for Engine block heaters

    The NEC does not define "public." But it does define "qualified person." In my view, the one is anyone who is not the other.

    In other words, the "public" is not intended to mean a person who is not an employee. It means a person who is not trained in the means and methods of safely working around, or even just being around, electrical equipment. The employees who park in this particular garage could well be accountants or truck drivers or administrative staff, none of whom can be expected to know what a GFCI does or why it is used.

    If these block heaters are tripping the GFCI receptacles, then there is a reason. You can't solve the problem by eliminating the safety feature that alerts you to the problem, and that protects you against the problem.
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  5. #5
    bthielen Guest

    Re: GFCI for Engine block heaters

    Why do you suppose the GFCIs are tripping? Seems to me that if they are, they are probably detecting ground fault current and therefore doing what they are intended to do. Excessive load should not cause a GFCI problem but it should cause the circuit breaker to trip instead. I use GFCI receptacles in three outdoor locations at my residence specifically for soft plug and tank heaters on my cars, trucks, tractors, etc. and I have not experienced any problems with this application. Are you sure you're not pointing your finger at the GFCI when in reality there actually may be a problem with the circuit?

    Bob

  6. #6
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    Re: GFCI for Engine block heaters

    I would guess that the problem is in the block heater itself, maybe age is a factor in most cases. I did a little more research after I posted here and discovered that the State code, WI, in this case does not require GFCI receptacles for engine block heaters. All they require is a rain tight while in use cover and a label stating the intended use of the receptacle.
    Tom

    " And all the science I don't understand, it's just my job five days a week "

  7. #7
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    Re: GFCI for Engine block heaters

    The only way the block heater could leak current and trip the gfi would be if the ground was bonded to the engine block via the heater itself? Is that in fact the case is there continuity between the ground on the cord and the metal body of the heater? If so then yes its possible. If not then current could not get back to the gfi any other way aside from the obvious grounded conductor which would not trip the GFI. Ill bet it may be moisture or weather getting into the extension cords. The Cords hot and ground are so close at the end that rain or snow can create a path way accross enough to draw 5 mil or so. Also add the possibility of any road salt aiding the continuity.
    Make something idiot proof and someone will make a better idiot.

  8. #8
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    Re: GFCI for Engine block heaters

    Originally posted by m73214:
    I would guess that the problem is in the block heater itself, maybe age is a factor in most cases. I did a little more research after I posted here and discovered that the State code, WI, in this case does not require GFCI receptacles for engine block heaters. All they require is a rain tight while in use cover and a label stating the intended use of the receptacle.
    So go for it

  9. #9
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    Re: GFCI for Engine block heaters

    Obviously there is some kind of ground fault. This should be checked into, because a hazard could result if you pull the GFI's out. Another thing to consider is electrolysis in the engine with the ground currents seeking other paths back.. This situation could get very spendy.

    I'd think twice before just pulling the GFI's when you know something's wrong.
    It's not rocket surgery!

  10. #10
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    Re: GFCI for Engine block heaters

    I agree there is a problem and should be looked into, in my experience the cords that get used are mangled and there is probably some sort of problem.

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