An electrician installed an outlet on a circuit inside my garage that is connected to an exterior spotlight. The spotlight has a sensor that automatically turns it on at dusk and off at dawn. There is an interior switch between the outlet and the light that controls the light only. The switch has to be on for the spotlight to respond to the sensor. I was told it would be a good idea replace the regular outlet with a GFI outlet before the Holidays since I connect the Christmas lights there. Everything was fine until I removed the Christmas lights. Now when I turn on the interior switch (it was off to allow the Christmas lights to be worked with a timer plugged into the outlet) to allow the spotlight to work with the light sensor, the GFI outlet goes off! Possibly of note: prior to putting in the GFI outlet there were no problems and the washer/dryer are on the same circuit. Is it possible the circuit is overloaded? The outdoor spotlight is 10 years old. Could replacing it with a modern light that requires less power make a difference?
The washer and dryer are on the same circuit? It must be a gas dryer?
I'd think that you would want to see about splitting this out on its own circuit if you can. The drum motors in the washer or dryer could be the culprit. GFCI only requires a 0.005A difference in current between the hot and neutral legs to trip.
Your GFCI outlet might be defective or over-sensitive.
There could be a small/intermittent short to ground in your outdoor spotlight fixture? Maybe the lamp itself is defective and causing enough fluctuation to trip the GFCI.
Do you have a moisture problem in the outdoor spotlight, perhaps?
The circuit might be overloaded, but that could not be tripping the GFCI. I assume the GFCI outlet was installed downstream from the washer/dryer so that they are not protected by the GFCI. You can confirm this by pressing TEST on the GFCI and see if the washer/dryer still have power.
The outdoor spotlight is probably damp, causing enough current leakage to trip the GFCI. If it was switched off for a few weeks over Christmas, moisture might have accumulated.
Remove the spotlight bulb. Does it still trip?
With the bulb still out, dry the socket and surrounding area with a hairdryer. Does it still trip?
With the breaker off, remove the spotlight fixture from its box, disconnect the black wire, and wrap some tape around the exposed conductor on the "power" side. Turn on the breaker. Does the GFCI still trip? If YES, call the electrician. If NO, remove the spotlight unit, take it indoors and put it in a warm place to dry out for a day. Then reinstall and try again.
GFCI's can easily be wired incorrectly, even by an electrician. It's quite possible that the wiring going to the outside light (which would be an "additional circuit" you want to protect) is wired to the "line" terminals instead of the "load" terminals, and the power to the GFCI is wired to the "line" terminals. IF wired correctly it won't do this.
It's also possible to bypass the GFCI for the light outside, BEFORE the GFCI, or the feed to the light simply connected to the "line" terminals (but this will give no ground fault protection to the outside light.)
I've seen this repeatedly.
See the diagram below "Here are the instructions for connecting in a 2-wire scenario." in the following post: How do I install a GFCI receptacle with two hot wires and common neutral?