Partial Outage in Apartment

Sorry for the slow response, but when in the process of taking out the breakers to investigate the bus bar I figured out what was going on and it took me a few days to confirm it. The two bad breakers were in the same row of my sub panel, and it dawned on me that if one the lines from the main panel that feeds sub panel was bad, that could be causing my problem. So I tested the two breakers (tandem) in the main panel that were feeding my sub and sure enough one of them was putting out 25V. So I replaced the tandem breaker in the main panel and now everything is working agin.

Thank for your suggestion about the breakers being in the same row, which got me thinking about the problem in a different way.

The "four rooms on a breaker" and the re-trip with a flash, along with the routine shutoffs owing to rewiring the poles... together completes the picture.

Four rooms is an enormous load for any circuit, especially when one of them is a kitchen. And this is a smaller 15A circuit. And there are "safety power strips"** and as such, I suspect there are also other loads which you did not mention or are unaware of.

In any case, this circuit is certainly maxed out.

It's also possible the fridge is getting old and tired, or even having a ground fault.

So here's what we know. When you reclosed the breaker, you got a flash, "foof" and retrip. And you did it again (bad move), same result.

Certainly it's reasonable to assume that if you manually shut it off, and later turned it back on, it would trip again. Ditto if you shut off the whole panel/house. Ditto if there was a power outage, and not all outages have to do with scheduled work. (This assumes the freezer has warmed up a bit and wants to cycle on: if the freezer is sanguine, it may not trip.)

This is an immediate, big-flash, magnetic mode trip, which only happens at 5 to 10 times a breaker's thermal mode current rating. What would cause that? Inrush current at startup - this is a characteristic of most motors, most lightbulbs, and most power supplies. And this explains why you can power everything up if you start each one at a time. The fridge's current draw is dramatically lower once its motor has spun up, so as long as you introduce each inrush current one at a time, you are OK.

Inrush current is why the breaker's magnetic trip rating is so much higher than its thermal trip rating. A great deal of it is tolerated.

On power restore, everything restarts at once and they are stacking to cause a magnetic trip. This shouldn't happen. Either one appliance is defective and causing an extraordinary startup load, or you just have way too much stuff on this circuit.

Inrush current applies every time an appliance cycles on, e.g. A fridge will turn on and off intermittently as needed. If two big appliances both happen to cycle at the same time, you will get a spurious, unexplained trip.

What you really need is a dedicated circuit for fridge and for freezer. If the landlord is fond of removing the panel deadface, this shouldn't be too much of a challenge for him, I see 3 empty spaces.

Or it may be time to replace an old fridge, or at least its motor's start capacitor.

Figure out which loads are on which breakers, and how much each load realistically draws... and move things around so they are sane. A Kill-a-Watt will tell you what any appliance or power strip draws. Unfortunately I don't onow of a device like that which will tell you about inrush current.

** "safety power strips" are not a thing, by the way. Strips are receptacle splitters, to give you 6 sockets where you had 2. Used well, they can be safe, but all the loads on them together add to the demand on the circuit, so it is exactly the same as if they were plugged in directly. So if the notion is "they let me plug more stuff in", that is only true if all their power draws add up to a sensible number.

As far as safety, they certainly add anything but that, and they are probably the cheapest and most shoddily made part of your entire wiring system (unless they're Tripp-Lite, then nevermind.) Perhaps they mean "as opposed to this other unsafe power strip".