I wired my Morton building using the three wire system of one neutral wire for alternating black and red hot wires. Wiring four receptacles per run, two black and two red each being on a separate 20amp breaker. My question is does circuit breaker placement matter? Is putting them in-line any better or worse then alternating them?
All shared neutral circuits must be wired to double pole breakers. There are 2 reasons. If someone puts a test light in one outlet, and turns off the breaker to that outlet, they can still get shocked because the other circuit is connected there. Also, when the 2 hot wires are on opposite phases, such as on a double pole breaker, the neutral carries the difference between the load. So, the load would never be more than 20 amps. However, if they are on the same phase it would be the sum of the 2 circuits. It could carry 40 amps. With no breaker on the neutral wire, it would overheat and possibly start a fire.
So, you will need double pole breakers, the kind that are associated with 220 volts.
Remember that on a shared neutral circuit, you have to connect the white wires using wire nuts then run a pigtail to the outlet. You can't connect both white wires to the outlet screws.