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High-density housing, especially high-rise, often has "network" power, a 120-volt 3-phase derivative that allows the efficient delivery and master-metering of three-phase service to the building. Without the added distribution transformers associated with even more efficient high-voltage bulk delivery, the power is fed to each dwelling as two of the three phases, each at 120 volts but separated by 120 degrees of the cycle, creating a maximum voltage of 208 rather than the optimal 240 that most single family houses receive.
Houses with 120/240-volt services are "single-phase" in that the second 120-volt leg is 180 degrees-out-of-phase with the first one and the meter just picks it up with a reversed coil and measures usage accurately enough for revenue billing (ANSI C-12 allows +/- 2%). A 120/208 volt circuit is "almost" single-phase and can be treated as single-phase with a +/- 8% KWH error** that mitigates (cancels out) over time. Kilovolt-ampere-hours (KVAH) are unaffected and can also be used to guage relative usage. This, however, is not "good enough" for government-assisted housing (HUD, Section-8, etc.) and may be questioned. The remedy is to meter both phases on separate channels at twice the cost. This can still be very cost effective.
As long as there is a master meter(s), owned and maintained by the utility, proportional allocation of the billed cost is perfectly legal everywhere. Ratio Utility Billing System, which is also referred to as RUBS or Allocation, involves the distribution of utility costs to users using defined, uniformly implemented methods. Common methods for per-unit allocation include number of utility-consuming fixtures, number of people, square footage or some such combination. Regardless of which utility is allocated, the process is the same and completely legal. In this case of almost perfect electrical metering (at half the cost), the residents are billed their part of the master meter total in direct proportion to their usage with absolute fairness over time. In the event that actual billing data becomes unavailable, provision for fallback to one of the RUBS methods above should be part of each tenant's lease agreement.
** IDK how many sales we may have "talked ourselves out of" b/c of this. At least one other vendor has the same simplified approach and says absolutely nothing about it. You can have full ANSI C12 accuracy and meet any legal requirements at any time with our equipment. If you simply want to allocate relative costs and make your tenants accountable, this is a substantially cheaper way to do it in this particular situation.
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