What are the limits (if any) of switching a 2-pole load with only one of its poles? Perhaps, if it is an automatic control then it is ok but if it is manual then it is not allowed? Also, does it matter if the single pole switching device is on the unit or in a remote location? For example, a 240v baseboard, electric heater may have a single pole, line-voltage thermostat (either on the heater itself or on the wall). However, take a 208 or 240v, single phase pole-light. Can I control it by a single-pole photocell on a nearby building (no 2-pole contactor or relay in between)? If so, why could I not also have a manual override switch that breaks only one line? Understand that I personally would not do either of these things and consider it "bad practice" whether it is code-compliant or not. Also, anything requiring an actual disconnect would need the breaking of all phase conductors but that is not a case I am considering.