Electrical Distribution Glossary

AIS

Air-Insulated Switchgear: equipment that uses air for defined insulation functions.

RMU

Ring Main Unit: compact MV switching and protection assembly, commonly used in secondary distribution.

VCB

Vacuum Circuit Breaker: breaker using a vacuum interrupter for current interruption.

SLD

Single-Line Diagram: simplified electrical drawing showing the main power circuit and key devices.

RTU

Remote Terminal Unit: field interface for monitoring/control systems.

FRTU

Feeder Remote Terminal Unit: RTU developed or configured for feeder automation functions.

SCADA

Supervisory Control and Data Acquisition: systems enabling supervisory visibility and control.

IAC

Internal Arc Classification: specified test classification for equipment's internal-arc performance.

IP

Ingress Protection: classification against the ingress of solids and water.

FAT

Factory Acceptance Test: purchaser/witness verification under an agreed test scope.

IEC 62271

A family of standards covering high-voltage switchgear and controlgear equipment in relevant contexts.

Rated normal current

current equipment can carry under defined normal operating conditions.

Short-time withstand current

current the assembly can carry for a defined short duration under specified conditions.

Definitions are educational; specifications must use the exact terminology and edition of the applicable standard.