Meter forms, often identified by their form numbers on electric meters, are crucial for determining the appropriate type of meter for specific services. With various form numbers in use and two primary service types—self-contained and transformer-rated—understanding these forms is essential for meter technicians. Let’s explore the common form numbers and the services they’re typically associated with:

Form 1s

Form 1s meters were once prevalent in single-phase, 120-volt two-wire services. However, their usage has declined as many homes transitioned to 240-volt services. Utilities favored this switch as it allowed for easy installation of Form 2s meters, which closely resemble Form 1s meters. Nowadays, Form 1s meters find application primarily in sign services requiring only 120 volts.

Form 2s

Form 2s meters stand as the most common form, widely used in single-phase, 240-volt three-wire services. They are commonly found in residential homes and small businesses.

Form 3s

Form 3s meters are employed in single-phase two-wire services requiring current transformers (CTs). They can also serve in three-wire single-phase services or single-phase primary metering setups, utilizing a single CT.

Form 4s

Form 4s meters are designated for single-phase three-wire services with two CTs. These transformer-rated meters are utilized when the service size exceeds the capacity of a Form 2s meter.

Form 5s

Form 5s meters, also transformer-rated, are versatile and applicable across various service types, from four-wire wye to three-wire delta configurations. They excel in three-wire delta services, offering insights into service type and voltage for efficient troubleshooting.

Form 9s

Form 9s meters find common usage in four-wire wye services and high-leg delta services. These meters are instrumental in accurately metering complex service configurations.

Form 12s

Form 12s meters are self-contained and adaptable for use in three-wire delta three-phase services or single-phase services derived from a three-phase transformer, such as network services.

Form 16s

Form 16s meters, also self-contained, are predominantly employed for metering four-wire wye services.

The Evolution of Meter Technology

With the advent of solid-state meters, features like auto-ranging have revolutionized metering practices. Auto-ranging allows for the use of Form 9s meters in four-wire delta services and Form 16s meters in four-wire delta services, simplifying inventory management for technicians.

Understanding meter forms is crucial for ensuring accurate meter installations and efficient troubleshooting. As meter technology continues to evolve, staying abreast of these advancements is essential for meter technicians.