Distribution Switchgear Glossary: Key Terms for Utility Buyers

This glossary defines the terms utility engineers, EPC specifiers, and procurement teams encounter when specifying medium- and low-voltage distribution equipment. Each entry links to a deeper explainer where available.

Devices & Switchgear

SF6 Load Break Switch (LBS)

A sealed, gas-insulated switch for making and breaking load current outdoors. Unlike a circuit breaker, it does not clear short-circuit faults. See the SF6 LBS technical analysis.

Pole-Mounted Circuit Breaker (PMCB)

An outdoor circuit breaker (vacuum or SF6) mounted on a pole that can interrupt short-circuit fault current — the device to specify when fault clearing is required. See the vacuum circuit breaker guide.

Auto-Recloser (Recloser)

An intelligent protection device that detects a fault, interrupts it, and automatically recloses after a set sequence — restoring supply for transient faults without crew intervention.

Dropout / Expulsion Fuse Cutout

A renewable overcurrent protector for overhead lines; the fuse tube drops out when the element melts. Common on distribution laterals for fault isolation.

Disconnector / Isolator

An off-load device that provides a visible, safe break for isolation and maintenance (IEC 62271-102). It is not for switching load or fault current.

IACM

Manually Operated Overhead switch — an air-break disconnector/switch-disconnector operated with a hook stick. Often confused with an SF6 LBS; see the IACM vs SF6 comparison.

Ring Main Unit (RMU)

A compact, SF6-insulated metal-enclosed switchgear for MV distribution rings, combining load break switches and optionally a circuit breaker in a small footprint.

Vacuum Circuit Breaker (VCB)

A circuit breaker that quenches the arc in a vacuum interrupter — the dominant technology for MV metal-enclosed switchgear (e.g., KYN panels).

Low-Voltage Switchgear (GGD / GCS)

400–690 V assemblies (to IEC 61439 / GB 7251.12) feeding transformers and distribution boards. GGD is fixed/economical; GCS is modular/higher-rated.

Protection & Insulation

Lightning / Surge Arrester

A device that limits overvoltage by diverting surge current to earth, protecting insulation. See the arrester explainers.

Composite / Polymer Insulator

An insulator with a fiberglass core and silicone-rubber housing — light, anti-pollution, and vandal-resistant versus porcelain. Includes pin, post, and strain types.

Pin / Post / Strain Insulator

Line and post insulators that support and insulate conductors; pin insulators sit on a pin, post insulators are vertical supports, strain insulators take tension.

IP Code (Ingress Protection)

An IEC 60529 rating of enclosure protection against solids and water (e.g., IP30 = finger/solid >2.5 mm, no water protection).

Testing, Standards & Certification

Type Test Certificate

Independent, third-party proof that a design meets a standard (e.g., IEC 62271-200 for MV switchgear). It is rating-specific and issued to a named manufacturer. See the type test certificate guide.

IEC vs ANSI/IEEE

The two dominant standards families — IEC (global, including China’s GB equivalents) and ANSI/IEEE (North America). Ratings and test methods differ; specify the family your market requires.

Short-Circuit Withstand (Icw)

The current a busbar/assembly can survive for the rated short-time duration (typically 1 s) without damage.

CQC / KEMA / XIHARI

Accredited certification bodies and laboratories: CQC (China, GB standards), KEMA (Netherlands, STL short-circuit testing), XIHARI (China, high-voltage apparatus testing).