That was probably me. I was shortcutting to the practical outcome.
Technically, NEC 2020 does not outlaw any tandem or quad breaker. But in reality, that fact plus $6 will buy you a small coffee at Starbucks.
In effect, most circuits need to be full-size breakers because they need to be GFCI, AFCI or both -- and those aren't made in tandem or quad
Say you want to feed a dryer. 2020 Code at 210.8 absolutely requires GFCI protection on that 240V/30A circuit. You can do that any of several ways.
- quadplex to a NEMA 14-30 GFCI receptacle (vaporware)
- quadplex via a 2-pole GFCI deadfront (unobtanium) to a 14-30 plain recep.
- GFCI quadplex (unlikely to ever exist).
- GFCI 2-pole breaker (takes 2 full spaces/4 "circuits").
See, the last one is the only option that is anything other than a fantasy.
Most circuits require AFCI (already). Now they require GFCI too, but that can be at the first recep. AFCI is tougher though.
- AFCI breaker that is twin (unlikely to ever exist)
- twin with conduit buried in 2" of concrete to the first recep, then AFCI+GFCI recep.
- twin with EMT conduit to the first recep point then AFCI+GFCI recep.
- AFCI full-space breaker. No twinning!
Again the first one is a nonstarter. You are unable to do the second and probably unwilling to do the third. We're back to a full-space breaker.
So hey, if we're that keen to save $40 on a panel, we're probably keen to save money on wire too. Let's grab the 14/3 and run circuits 2 at once with a multi-wire branch circuit. Ah, but we need AFCI/GFCI.
- Quadplex breaker, common shutoff. Run EMT to the first outlet (2-gang) then fit dual AFCI/GFCI receps there, then separate /2 cables onward to everywhere else (available, but basically defeats the purpose of MWBC and is a nightmare).
- 2-pole AFCI/GFCI breaker (and you're free to MWBC at will).
In this case, it's technically possible to double-stuff... but the burden (running EMT, /2 after the first recep) pretty much defeats any possible savings. Again the winner is a full-size breaker.
Backfeeding a breaker? Needs a tie-down kit. They don't make tie-down kits for quadplexes.
Want to power a TT30 recep (had several come up this week)? Okeydokey.
- A 30/30 twin is fail, because there's no practical use for a 120V 30A circuit *except* a travel trailer, so it'll be wasted. That defeats the purpose of twins, so no.
- A 30/20 twin and then we feed it through a 30A rated GFCI deadfront (oh wait, that doesn't exist).
- A 30/20 twin and then we feed a TT30 GFCI receptacle (nonexistent).
- A full size 30A 1-pole GFCI breaker (vaporware)
- A full size 2-pole 30A GFCI breaker, and only use half of it
Unfortunately again the last one is the only one which is possible... and now not only have we completely failed to twin, we're using 2 spaces/4 circuits! We're actually stepping backwards here!
Have a feeder to a small subpanel.
- Fit a 50A GFCI breaker in the main panel. Feed a 4-space/8-circuit panel. Fill it with double-stuffs feeding circuits that do require GFCI but do not require AFCI (lotsa luck with that lol).
Take a picture. This is actually one where double-stuffing wins
. However there are 2 snags. #1 Oh, snap. We forgot about AFCI. On AFCI circuits we're back to full spaces again - well, it was nice while it lasted
. #2 there's a reason Euro whole-house RCDs trip at 30ma not 6ma. Most devices have leakage in the micro-amp range (e.g. smart switches are specifically allowed 500uA=0.5 ma). Feed too many things with the same GFCI, they add up. And you can find yourself with a lot of nuisance trips, which again, defeats the purpose.
So yeah, technically, you've spent hours raking through Code and you've chiseled out a right to double-stuff 2, maybe 3 circuits in your home. So I'm not *technically* correct. But what has this really bought you, in the end?
Does it save you money on panels? Can you chintz out on a 20-space/"40-circuit" panel and expect that to support a whole house, straight-faced? No. Not anymore under NEC 2020, but that die was cast in NEC 2014. 2020 is just driving the last coffin nails.
I know how hard this is because I'm (voluntarily) trying to bring several Pushmatic boards up to modern NEC ('17; '20 is not gonna happen), and it's the same problem-set as trying to AFCI/GFCI double-stuffs.
Considering how a tandem will be needed to be used in the newer panels like a 30/60 or a 40/80 it would not make much sense. Mike Holt never said anything during his code update course.
So you're saying that tandems are necessary, otherwise the circuit panel advertising claims such as "30-space/60-circuit" would make no sense whatsoever.
Yeah, they make no sense whatsoever.
And haven't for awhile. Those advertising boasts have no place in a post-NEC 2014 world. I do not know what possessed those companies to have continued it; they misled a lot of novices.
2014 is when NEC "crossed the Rubicon" with regards to this smothering demand for AFCI/GFCI everywhere. Since most of this actually goes back to then, I can imagine why it wouldn't be heavily discussed in 2020. Heck, the requirement for 240V circuits to be GFCI (which I'm sure was mentioned) is barely a footnote. It just has an outsize impact on double-stuffing, since 240V circuits gobble up breaker slots two at a time.