Customer Drop and Metering Equation
Since electrical standards vary in different regions, "customer drops" from the grid to the customer also vary depending on the standards and the type of installation. There are several common types of connections between a grid and a customer. Each type has a different metering equation.
Customer supplies may be single-phase or three-phase. In the United States and Canada, three-wire single phase is common for residential and small commercial customers. Three phase supplies may be three wire, or four wire (with a system neutral). Blondel's theorem states that for any system with N current-carrying conductors, that N-1 measuring elements are sufficient to measure electrical energy. This indicates that different metering is needed, for example, for a three-phase three-wire system than for a three-phase four-wire (with neutral) system.
In North America, it is common for electricity meters to plug into a standardised socket outdoors, on the side of a building. This allows the meter to be replaced without disturbing the wires to the socket, or the occupant of the building. Some sockets may have a bypass while the meter is removed for service. The amount of electricity used without being recorded during this small time is considered insignificant when compared to the inconvenience which might be caused to the customer by cutting off the electricity supply. Most electronic meters in North America use a serial protocol, ANSI C12.18.
In many other countries the supply and load terminals are in the meter housing itself. Cables are connected directly to the meter. In some areas the meter is outside, often on a utility pole. In others, it is inside the building in a niche. If inside, it may share a data connection with other meters. If it exists, the shared connection is often a small plug near the post box. The connection is often EIA-485 or infra-red with a serial protocol such as IEC 62056.
In 2010, networking to meters is rapidly changing. The most common schemes seem to combine an existing national standard for data (e.g. ANSI C12.19 or IEC 62056) operating via the internet protocol with a small circuit board that does either powerline communication, or ties to a digital mobile phone network.
Read more about this topic: Electricity Meter
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