Engine block heaters

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texie

Senior Member
Location
Fort Collins, Colorado
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Electrician, Contractor, Inspector
Those of us in extreme cold areas where block heaters are common know of the issues with engine block heaters and GFCI s tripping. Most often there is a reason for these trips but you get the occasional story of a brand new vehicle and otherwise correct and clean wiring tripping GFCIs. I often get questions about any code allowances for using no GFCI or using GFPE (30 mA) as an alternative. It is my position that there is no allowance for this no matter what the occupancy is as these are all plug in devices and all outdoor outlets must be GFCI protected no matter of the occupancy type.
Seems pretty clear to me but what say others?
 
ptonsparky said:
It never hurts to replace a GFCI device with another and occasionally a different name brand works. IDK why.
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A slightly defective receptacle or just a cheap brand is my guess why that sometimes works.

I once had one GFCI that would trip occasionally when a light on another circuit was turned on or off. The GFCI had to be responding to a short surge of current caused by the switching.

My guess is that receptacle had a bad capacitor or something that was supposed to filter out transients. Or another possibility it was just so cheap that it lacked any filtering at all.

Wiring length is something else to think about. If they have a 200' extension cord running out to the vehicle, it could have a substantial amount of leakage in the cord itself.
 
A majority of those I have had calls with was not the heater but rather an extension cord with a fault, moisture in cord cap/plugs, cord/cap plug actually laying in water, or on occasion the heater cord has a fault/damages.

Hint: Sometimes with moisture issues you can clear the fault by temporarily plugging the offending cord or equipment into an non GFCI protected outlet and let it burn itself clear, but maybe not so good to tell customer to do that, they won't understand what is really going on and take that to mean they can just use a non GFCI protected outlet all the time.
 
steve66 said:
A slightly defective receptacle or just a cheap brand is my guess why that sometimes works.

I once had one GFCI that would trip occasionally when a light on another circuit was turned on or off. The GFCI had to be responding to a short surge of current caused by the switching.

My guess is that receptacle had a bad capacitor or something that was supposed to filter out transients. Or another possibility it was just so cheap that it lacked any filtering at all.

Wiring length is something else to think about. If they have a 200' extension cord running out to the vehicle, it could have a substantial amount of leakage in the cord itself.
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That is my vote for those "cheap" generic type named units sold at some big box stores.
 
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