Based on discussion from the labs WG, we would like to propose the following new tag choice on ac-elec-meter and motor:

def: ^phaseCount
is: ^choice
doc:  
  Number of phases for an AC electrical power system or 
  connected equipment: single-phase or three-phase.
---
def: ^singlePhase
is: ^phaseCount
doc:
  Single-phase AC electrical power. Power is provided by a 
  single AC voltage source.
---
def: ^threePhase
is: ^phaseCount
doc:
  Three-phase AC electrical power. Power is provided by three AC voltage 
  sources, each separated from the others by a 120-degree phase angle.