I am a bit confused by the question - I think you're saying there's a 40 amp panel with a 20 amp two pole breaker for an air conditioner you want to add a 30 amp breaker for a washer dryer unit, and you want to make sure the washer breaker and the air conditioner breaker don't go on at the same time. (Also, are you thinking break before make, and have it reversed in the question's title?)
Would it work to use a 30 amp DPDT switch on a 30 amp breaker, one throw going to the washer dryer, the other going to a disconnect with a 20 amp breaker feeding the existing air conditioner? For example this one
Hubbell 1388
looks at a glance like it would be adequate.
The AC and it's existing wiring probably has to be on a 20 amp breaker, so you couldn't just connect it to the switch. I think you could find a 20 amp disconnect to go between the AC throw of the switch and the existing wiring.
Is there another panel for the apartment? With all this on 40 amp main I'd see a lot of trips.
That is an old "rule of six" panel, which while grandfathered, is illegal under its grandfathering becuse it has 7 main breakers. Going to five is a good plan.
It is a classic "CH" panel which is a very good industrial grade panel, except that the 3/4" breaker width make non-ordinary breakers very expensive (a trait it shares with Square D QO). That makes it perfect for what you plan.
On your subpanel which would be near this panel, I would get a panel with a main breaker, with an eye toward (at some point in the future) cutting it over to be the main panel. In a subpanel, the "main breaker" is nothing more than an on/off switch, it is OK for it to be larger than the feeding breaker.
I would also get a rather large panel, at the very least 42 space and even 60 or 84 if practicable: because panel spaces are dirt cheap and often even come with free breakers, whereas running out of space is painfully expensive.
I would aim for an industrial grade panel of good repute (one available in 3-phase variants, not Homeline, BR, or second tier brands) and avoid the expensive 3/4" breakers (not CH or QO).
Over time, as you find it convenient, i'd migrate all your 1-pole and smaller 2-pole circuits over to the new panel.
For your garage panel anything would do, but I'd go for the same type as your indoor panel, so you can use some of those bonus breakers. Again it's false economy to scrimp on spaces, I'd go 20-30 at least.
Also, since garage spaces need to be on GFCI, consider getting a subpanel which has a "main breaker" which is GFCI, that way all the breakers in that panel would be protected (at the cost of potential nuisance trips, a big deal if you keep a freezer in the garage).
Ed Beal raises some very good concerns about overall capacity. One problem with these "rule of six" panels is there is literally no main breaker to stop you from drawing more than 150A. So it pays to be conservative.
It's a difficult situation because you have two big loads that operate sporadically - the EV charger and the range. And the A/C as a wildcard.
One thing I might suggest, is feed the garage subpanel from the new primary subpanel. And then move everything but the range over to the new subpanel. At that point the only things still in the CH panel would be a 60A range breaker and a 100A subpanel breaker. Even at max, those two could not overload the 150A service (by enough to matter). This would force your entire house (from A/C to EV charger) to share 100A, but would remove the possibility of an overload. This would also save you the $85 you'll spend on a second 100A CH breaker.
Best Answer
#1 is it normal to have a 100A-breakered panel downline of 60A overcurrent protection? Totally legal. But I'd use a 225A panel. One thing many of us here agree on is running out of panel spaces is bad, and panel spaces are cheap. Both better and cheaper to get a 42-space panel today and only ever use 18 spaces, then get a 12-space panel today have to retrofit a 20-space panel tomorrow and a 30-space panel later still when you add an electric car -- that's just dumb. The big panels we prefer come with big 150-225A breakers, and they often come with "bonus breakers" and ground bars included, so the extra cost can be a wash.
#2 Breakers and fuses protect wiring downstream. Without the 60A fuse, the jumper into your house (#6?) would have no overload protection at all, and if the cable became shorted, nothing would interrupt current and it would burn your house down.
#3 If you want to increase service above 60A, talk to your power company Your service capacity will be limited by the lowest of
It's possible to get combination meter pans/main breakers, with the main breaker serving as the shutoff switch and replacing the fuses. The main breaker and the feeder rules decides the wire size downstream of that breaker.
As far as where is the main grounding point located, some sticklers say the grounding point must be the outside fusing/shutoff switch. However that is awkward in your situation, and for ground-siting purposes I am very comfortable disregarding the outside shutoff and putting the grounding hub in the main panel. They're built for that, and shutoff switches are not.
This presumes there is one main panel. If you fork lines to two panels off that outdoor switch/breaker, things get really complicated.