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  • What? A mwbc that is on 2 full-size handle tied breakers the neutrals are 180 out of phase so they will not be over loaded. With single phase an overload will trip the breaker 100% of the time the neutral is not overloaded. The 2 separate circuits can go different directions and be controlled by whatever switch. Commented Jun 8, 2021 at 21:46
  • @EdBeal Absolutely not a problem of neutral overload. My concern (and I think my wiring changes account for this appropriately) is that if you have one switch on /3 = hot-A/load/neutral and the other switch on /2 = hot-B/load then if switch 2 itself uses neutral (borrowed from the /3) then there won't be a balance/matched current in the /3 cable. Switch A is off and drawing 1 watt in standby. Switch B is functioning and drawing 10 watts (broadcasting WiFi, whatever...) - the /3 will have 1 watt on hot, 10 watt on neutral = unbalanced = bad (eddy currents?) Commented Jun 8, 2021 at 21:57
  • @EdBeal If you had two GFCIs - one for each branch - in that main junction box, the simple "grab the neutral from the other switch" would result in both GFCIs tripping. Commented Jun 8, 2021 at 21:59
  • try again gfci’s will nuisance trip without a switch that’s why pros like me don’t use them much any more a multi wire branch circuit is just that all the return goes back on the neutral. Commented Jun 8, 2021 at 22:11
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    Thought experiment: Future owner decides they want a convenience outlet in this switch box. Grabs hot and neutral that are going to switch B. Plugs in a portable heater 1,500W. Now that /3 cable has 1 watt (standby current of switch A when "off') on the hot, 0 watt on switched hot *and 1,500 W on neutral. That /2 cable now has 1,501 watt on hot (1 watt standby for switch B when "off" + 1,500 W for the heater) and 0 W on switched hot. So each cable is essentially a single wire at ~ 1,500W instead of a pair (or triple) of balanced wires. Commented Jun 8, 2021 at 22:24