Standard parameters of primary distribution boxes

Primary distribution boxes typically operate at medium-voltage levels (commonly 11–33 kV), include protective devices like circuit breakers and fuses, and are designed to distribute power safely to multiple feeders or sub-distribution points.

Voltage and Current Ratings

Primary distribution boxes are generally designed for medium-voltage systems, often ranging from 11 kV to 33 kV, depending on the country and network structure. The current rating of the main busbars and feeders is selected based on the maximum load demand, typically ranging from 400 A to several kiloamperes for industrial or utility applications.

Switchgear and Protection

These boxes usually house metal-enclosed switchgear, which can be air-insulated (AIS) or gas-insulated (GIS), providing both operational safety and compact installation options. Protective devices include: Circuit breakers for feeder protectionFuses for lateral tapsReclosers or sectionalizers for automatic fault isolationResidual Current Devices (RCDs) or surge protection for sensitive equipment Configuration and LayoutPrimary distribution boxes serve as the interface between the substation feeders and downstream distribution networks. Typical configurations include: Radial systems: Single feeder per area, simple but less reliablePrimary loops: Two feeders interconnected with normally open tie switches for improved reliabilitySpot networks: Multiple feeders supplying a concentrated load, ensuring high reliability for critical customers The boxes often include busbars for power distribution, incoming and outgoing feeder terminals, and may be designed for indoor or outdoor installation depending on environmental and space constraints.

Enclosure and Environmental Considerations

Primary distribution boxes are usually metal-enclosed for safety and durability. They may be rated for IP protection to prevent dust and water ingress, and can be installed indoors, outdoors, or underground.

GI

S technology allows the entire installation to be compactly housed inside a building.

Additional Features

Monitoring and metering: Some boxes include electronic meters for voltage, current, and power monitoringFlexibility: Designed to accommodate multiple feeders and future expansionSafety: Minimized exposed wiring and clear separation of high-voltage and medium-voltage sections In summary, primary distribution boxes are engineered to safely distribute medium-voltage power to multiple feeders, protect equipment and personnel, and provide flexibility for network expansion, with standard parameters defined by voltage level, current rating, protective devices, and enclosure type.