Electrical Metering for Linemen and Techicians


Self-Contained vs. Instrument Rated Meters

Self-Contained Meters

Self-Contained meters contain everything needed to meter the electrical circuit. The customer’s energy requirements pass directly through the meter. No auxiliary devices are required. In recent years, special self-contained meters have been designed to operate up to 320, or 400, or 600 amps depending upon the manufacturer. However, these meters require special meter sockets to handle the additional load. This manual will assume the maximum limit for all self-contained meters is 200 amps.

Self-contained meters are available with voltage ratings up to 480 volts. However, when an inadvertent electrical arc is created with voltages above the threshold of 308 volts, the arc will become self-sustaining. Installing and removing 480 volt meters should be considered extremely dangerous! Therefore, this manual will assume instrument-rated meters should be used for 480 volts and above.

Instrument-Rated Meters

Instrument-rated meters are designed to work with auxiliary devices referred to as instrument transformers. The two basic types of instrument transformers are current transformers and voltage transformers. When used in conjunction with these devices, the instrument-rated meter is capable of metering high currents and high voltages. This manual will assume that instrument-rated meters must be used when any load exceeds 200 amps or requires 480 volts and above.