In a house built in the early 1980s in California, USA.
My kitchen and dining room are (mostly) on a single pair of 20 amp circuits - excepting the dishwasher and garbage disposal, which each get a 15A circuit, and a "Microwave" circuit which is entirely inappropriately located above the oven (maybe they planned to have a Microwave/range hood) in a spot only the range hood can utilize. The pair of circuits are handle tied, so my guess is they are most likely a multi-wire branch circuit. (And yes, I know this is nowhere near current code - it's a rental, unfortunately, so limited options for changing things.)
Unfortunately, due to the inaccessible "Microwave" circuit, I have to attach both my microwave and toaster oven to the main set of circuits (but have some choice over which outlet to use for each, as I can move them around). Is it possible to determine which outlet is on which circuit of the pair, without opening the wall or doing anything significant to the panel? And if I determine that, say, these outlets are on "5" and these outlets are on "6" (the numbering in the panel), am I correct that it would work to have the two appliances on one each, and wouldn't trip (assuming other things weren't utilizing the circuits), since each would be on a different hot leg?
Ideally I'd either temporarily un-tie the two circuits and intentionally trip one, and then see what works and what doesn't, or have some way of telling which is which using the multimeter. (I'm also considering running an extension cord to the microwave plug, as ugly as that looks, because it certainly isn't a good idea to have two 1200+W appliances that often will be run at the same time on one circuit; but hoping there's a way to have one on each hot leg.)