I am still confused over the installation. Are you saying that a 3-pole breaker serves more than one piece of equipment, with each of the three phase conductors serving only one piece of equipment, and with a shared neutral? Is this, in fact, a MWBC? If so, then I would say this does not meet the definition of, ?Branch Circuit, Individual,? as provided in Article 100. Please note that the NEC does not define ?Dedicated Branch Circuit,? so for clarity let us stick with the phrase ?individual branch circuit.?
My reasoning starts with the fact that a ?branch circuit? is defined in terms of wires only. The breaker is not part of the branch circuit, and neither is the load. At least, that is how the Article 100 definition of ?branch circuit? is worded. So a three phase MWBC will have four wires, and all four of them are part of the branch circuit. So if the phase A wire and the N wire serve one load, and if the phase B wire and the neutral serve a second load, and if the phase C wire and the neutral serve a third load, then the branch circuit, as a whole, serves more than one load. So it is not an individual branch circuit.
One more thing I would like to bring up. Do I understand that the ATM will plug into a standard duplex receptacle outlet? If so, then even if you used a single pole breaker, and ran a separate neutral serving just that one receptacle, I could argue that this is not an individual branch circuit. A duplex receptacle is not a piece of ?utilization equipment,? and two pieces of utilization equipment can be served by that singe branch circuit.