Large residential condominium and apartment buildings often opt for master metering where the local power company installs a single electric meter to record energy consumption for the entire building. Master metering offers less expensive wholesale rates. The building owner or management company receives one electric bill and uses submeters to assess tenants their share, based on submeter readings, of the utility expense. Master and submetering should not be confused with direct metering, where the utility company bills tenants directly.
Onwership and Maintenance
The main difference between a master meter and submeter is ownership and maintenance responsibility. The power company owns and maintains master meters while submeters are owned and maintained by the commercial customer. Operational and repair issues and billing questions related to master meters are directed to the local utility. Concerns and questions for submeters are referred to building management
Billing and Collection
Billing and collection is another differentiating factor between master and submeters. The local power company gives the building management a monthly bill for usage recorded on the master meter. To recoup this expense, management then assesses each tenant or homeowner his fair share of the total utility expense according to the readings registered on their respective submeters. Energy conservation is encouraged with submetering as people become more aware of their consumption patterns as opposed to a flat rate cost structure for unlimited electricity usage.
Master meters and submeters work according to the same technical principles and physically look alike. The electromechanical meter with its signature glass bowl cover and spinning metal disc and the solid-state model with its plastic or polycarbonate cover and liquid crystal display are familiar types of conventional meters. However, master meters can be identified by the local utility's name or logo and meter badge number stamped on the face of the meter.
Meter readers from the power company read master meters whereas submeters are read by building management personnel. In high-rise condos and apartment buildings where submeters are used, the prospect of manually reading dozens of meters each month is a daunting task. A more cost-effective solution involves devices that automatically send meter information directly from each tenants' or homeowners' electric service panel over the buildings existing power cables using a technology called power line carrier. A computer located in the basement or ground floor collects the data for rebilling.
A master meter must be installed in front of any submeter, so the energy supplied to the building first flows through the master meter. The sum of the readings from each submeter should total what is displayed on the master meter.
Master meters and submeters also differ by their power handling capability. The large amount of power demanded by an entire building cannot be directly applied to a single master meter without ruining the meter. Instead, instrument transformers are often used with master meters to reduce the power to a safe level that the meter can handle. In contrast, the loads handled by submeters are not usually large enough to need these devices.