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I purchased a new Genie 1hp garage door opener Model Excelerator II and installed it but when I plugged it in (to GFI circuit) it sparked as soon as the connection was made but didn't trip the GFI. I could turn the openers light on and off but as soon as I tried to open the garage door it immediately tripped the GFI. I reset the GFI tried several times with the same result. So I ran a HD extension cord into the laundry room and plugged it into a non GFI washer circuit. It sparked again at initial connection but now I could activate the garage door up and down. I called the Manufacture and told them the problem I was having. They said the sparking when it is plugged in is normal because this model does not have physical limit switches and is always hot causing the spark. After long discussion they sent me a new circuit board to install (without any instructions to check the wiring). I have tested my Garage door circuit with heavy duty tools, grinders, heat gun and no sparks or tripping. What can be causing it to trip The GFI? Could they have the neutral and hot crossed in the circuitry of The Garage door opener?

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The answer to this is a wee bit complicated.

The Genie Excelerator II uses a DC motor and an electronic adjustable speed drive (ASD) to open a garage door quickly. If you look at the “Operation and Maintenance” manual, you will see a slightly ominous note in “General Troubleshooting – Opener does not run” that reads, “[Check for] a non-compatible GFCI. NOTE: A licensed electrician must replace non-compatible GFCI’s.” They do not say why the note is there.

It turns out that GFCI’s are frequency sensitive and an ASD produces high frequency harmonics that are electronically generated. If the ASD happens to generate harmonics in the GCFI’s sensitive area, then bingo, the ASD and the GFCI are not compatible.

Here’s a link to a helpful technical paper on the topic:

http://www.jonathankimball.com/pdf/gfci_ecce.pdf

In commercial and industrial environments, appropriately sized inductors called “line reactors” are installed upstream and/or downstream of an ASD to filter harmonics that would otherwise cause electrical problems. In a residential setting I imagine such a measure is not worth it. The implication of the language in the Genie manual is there are GFCIs for homeowners on the market that contain internal filtering to mitigate the ASD compatibility problem.

EDIT: The specifications for GFCIs tolerant of ASD loads should indicate they are a "high harmonics" type.

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