The microwave oven has been tripping the GFCI that it’s plugged into almost daily, whereas it never has before unless the toaster oven was accidentally used at the same time. It’s a 1000-watt oven, probably 4 years old, give or take. The GFCI was installed by an electrician maybe 15 years ago.
I assume this mean it’s dying? Is it unsafe to use in the meantime?
Is this a GFCI outlet device? AFAIK, those aren’t overcurrent protection circuit breakers, which is usually what begins to degrade with age.
I suppose a GFC may spuriously trip if it’s old and degraded, but I would also carefully consider whether maybe it’s something on the circuit causing a current imbalance and a genuine GFC trip, rather than the GFC acting up.
It could be a problem with the GFCI, with the microwave, or with the wiring. GFCIs can trip due to overload, but their primary purpose is to detect leaks across the hot and neutral wires. A bad GFCI outlet is less of a concern than a potential short in the oven or wiring, which could be bad.
Do you have another GFCI circuit nearby that you could plug your oven into and see if that one trips? If yes, get a new oven. If not, replace the GFCI.
I would guess that there is goop from cooking in the power supply, creating a small current leak to ground. Probably not a DIY fix, unless you are particularly handy.
If you suspect the GFCI, you can certainly replace it. At worst, you’ll discover the problem continues even with the new GFCI, in which case you can move on to the next likely culprit: the microwave.
The classic related issue is toasting frozen bread. Condensation forming inside the toaster can trip GFCIs. So nuking stuff that gets very steamy isn’t a stretch to imagine causing issues.
Anything that can lead to a slight leakage path is going to be a problem. If not related to food being nuked, other sources of grunk in a kitchen may also be the root cause.
Anecdote from a friend of mine years ago. His mother had just paid to have a GFCI installed on the house, back when they were pretty new. She was complaining about the price.
He was doing some handywork for her, and drilled into a beam. On the other side of the beam was a mains run. The drill went straight through and into the wiring. He got a solid jolt, and the GFCI tripped.
Quoth he to his mother. “That just paid for itself.”
I have had to chase down annoying faults that tripped a GFCI. Water leaking onto an outlet was a sobering one.