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It never happened before until I bought a new AC (15amps). The building electrician suggested I plug the unit on one of the kitchen 40amps double plugs, but happened again. After 4 black outs to my apartment the management decide to change my fuse box to a new beaker box. It worked for an hour and then the building main breakers tripped again, the last time the toaster/air fryer was the only appliance working. My breaker box have 6 ports 15amps each, 2 double ports 40amps each plus 1(I think 40amps) for the stove. Total 210amps, does anyone knows what the max. capacity of the main breaker should be ? Is it possible that the main breaker is weak (after tripping about 8 times in the past 10 days) and should be replaced ? I live in Toronto, Canada. The superintendent is no very cooperative and getting upset because regardless of the time of day (even when is off duty) it happens has to drop everything and reset the breaker on the top floor of the building. Any ideas will be greatly appreciated.

Eduardo
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    Please post photos of your breaker box and the electrical info plate/sticker on your AC. 40A is a puzzling number - perhaps you are referring to two 20A breakers with their handles tied together in the break box? – Armand Jul 17 '23 at 04:35
  • Can you try a different plug? – Gil Jul 17 '23 at 13:47
  • If the main breaker for the building is tripping, that means total consumption of the whole building is exceeding its capacity. So you may only have 2 appliances in use, but what is everyone else in the building using at the same time? If it's really the main breaker for the whole building, you (the building management, that is) should have a qualified electrician come take a look and do a full assessment. – FreeMan Jul 17 '23 at 17:26
  • Each double plug has two separated powers cables from the breakers box. in other words line 7 power goes to plug A top, line 8 to plug A bottom, line 9 to plug B top and line 10 to plug B bottom. I just checked and they are 15amps on each line (no 20amps like the electrician said). Total 30amps for each plug and not 40amps. Line 11 & 12 are controlled by a breaker with their handles together for the stove. EACH is 40 amps total 80 for the stove itself. Total for the panel is 10 x 15 amps = 150 plus the stove 2 x 40 =80 amps. But none of them trips only the building main breaker keeps tripping. – Eduardo Jul 17 '23 at 17:34
  • Each apartment (there is about 120 units) has its own main breaker. Mine is the one that keeps tripping. The other apartments have no problems. Is my main breaker in the building panel box (no my apartment breaker box) that after tripped over 10 days ago keeps tripping even with only one appliance (some times) working. That is why I thing they should replaced that breaker (I do not know how many AMPS it should be considering that my panel total breaker amps is 230amps). Is there a rule of thumb, like 100amps max or 150amps max ? – Eduardo Jul 17 '23 at 17:47

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"Selective coordination" is the feature you are looking for. It is a feature of costly industrial-tier breakers. There would need to be a main breaker in your panel for this to work.

To count breakers vs main breaker amps effectively, you really need to understand how 120/240V power works, and how panels are phased. Also, it is normal for breaker sums to exceed panel rating, because of the statistical improbability of having all of them at once heavily loaded. Of course, no one would know this better than you, since you are capable of mapping your circuits and looking at the nameplates of each appliance plugged into them. This is your responsibility anyway, since you must know which things are plugged into which circuits, so you can assure you are not overloading a circuit.

If you are not doing something odd/unlucky, like happening to have a bunch of 120V loads on one phase (see links), then there's no reason for the main breaker to be tripping.

Consider buying a Kill-A-Watt so you can harvest info about appliances where the nameplate isn't easy to reach.

On air conditioners, 1-hose portables are very inefficient because of handling the air stupidly (because customers prefer the aesthetics of 1 hose instead of 2 [??? what does that even buy you???]), so they take much more power for the same cooling. The 2-hose portables are much better, handling air in a way which makes efficiency a possibility.

Harper - Reinstate Monica
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Main breaker blowing suggests there may be a wiring problem in the breaker box itself... Or just that the main breaker is reaching end of life and should be replaced. Or that the breaker which should be blowing is malfunctioning and should be replaced.

keshlam
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It's very common that if you add up all the breakers in your panel, it comes to more than your main supply breaker or fuse. There's an assumption that you won't turn everything at once, and it's a lot cheaper to provide a smaller supply.

Unfortunately, it sounds like you are turning on too many things at once. The individual breakers in your panel don't see a problem, but you're overloading the main breaker.

There isn't really any "correct" value for that main breaker. You won't know what rating it is without looking. Maybe it's only 100A. Don't assume that upgrading it to a higher breaker will be free.

Simon B
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  • That is indeed another possibility. And "only" 100A on the main breaker used to be pretty standard for full-sized houses; that convention went up to 200A as people started using more electric gadgetry, and might have started coming back down as efficiency improved if electric vehicles and heat pumps and other larger-consumption items hadn't been introduced. The "correct" value depends on the wires on the electric company side of the breaker. – keshlam Jul 17 '23 at 23:30