Faulty (Sparking) Single-Pole Switch in One Room Trips GFCI Outlet in Another Room

Question

I am in the middle of updating the wiring in my ~100-year-old house. All switches, lights, and outlets on the second floor are on the same circuit from the breaker. Yesterday, I installed a ceiling fan in a second floor room, with dual single-pole switches (a two-switch device) controlling the fan and light separately. I could immediately tell that the fan switch is faulty. It is noticeably harder to flip than the light switch right below it, and I can see a spark in the switch when I turn the fan off. The reason I’m posting this is that I am confused by some other phenomenon I noticed occurring occasionally when switching off the sparking fan switch: Sometimes the GFCI outlet in the bathroom (different room than where I installed the ceiling fan) trips. Is this something to be expected with a faulty switch (and if so, why?), or does it indicate another issue somewhere else in the wiring? See diagrams below. One shows how the ceiling fan/light combo is wired, and the other shows kind of the basic (partial) circuit layout from the attic. I’ve also attached a picture showing the spark as I’m turning off the fan.

Note: I already have a replacement double switch on hand, but I haven’t yet installed it. I am planning to do that today, but I’m worried about the cause of the GFCI outlet tripping, and I really need to understand that to feel comfortable with the work I’m doing.

Another Note: I found a few similar questions on this site (see links below), but I think my situation is different enough that it warrants my posting a new question.

GFCI trips when flipping light switch in another room

GFCI Trips Single Pole Switch

Turning on light fixture trips GFCI on a different circuit

UPDATE: I have two other recently-installed ceiling fans on the same circuit (for a total of 3 fans), both of which can be controlled with wall switches. After messing around with those other two switches (i.e. turning the fans on and off repeatedly), I've found that each of the three ceiling fan switches is capable of tripping the GFCI outlet in the bathroom (though I don't see or hear sparks in the other two switches when turning off the fan). I don't know what this means, other than that, I guess, the inductive loads from the fan motors are somehow causing "nuisance trips."

Answer 1

There's nothing "defective" about a switch that sparks when disconnecting an inductive load (e.g. motors). That is to be expected, if there's no provision made at the load to prevent excessive voltage spikes. If anything is "defective", it's the fan. There's also nothing particularly concerning about the GFCI tripping, as those are, and have been since their inception, sensitive to the electrical noise and surges associated with some types of loads (motors, microwave ovens, even just incandescent lamps burning out, etc). It's called "nuisance tripping". This is not to say that some other brand of switch or GFCI might not have less of those undesireable traits.

One thing you could try to reduce any arcing at the switch, is to find one with a "DC" (direct current) rating. They are made to better resist arcing. DC does not have the inherent self-extinquishing properties of ordinary alternating current that common household switches are made to work with.