ALBORGRID › Guides › Switchgear & RMU Selection Guide
Start with where the assembly operates in the distribution system. Then confirm rated voltage and current, fault level, circuit arrangement, switching device, protection, interlocking, installation conditions and required project documents.
Medium-voltage switchgear, ring main units and low-voltage switchgear serve different points in the distribution system. Select the equipment family first; model and configuration follow only after the single-line diagram and electrical duty are clear.
For primary and secondary distribution where metal-clad or metal-enclosed assemblies and circuit-breaker switching are required. Choose fixed or withdrawable construction from the operating duty, maintenance strategy and approved specification.
For compact ring networks, cable distribution points and secondary distribution. Select the functional-unit arrangement and insulation approach after confirming the load-switch, fuse, circuit-breaker, metering and automation duties.
For distribution downstream of transformers and other LV system nodes. Choose fixed, withdrawable or compartment-type construction according to the circuit schedule, continuity requirement, maintenance access and project layout.
Use the single-line diagram to establish the equipment role, then work through the ratings, circuit arrangement, construction and secondary functions in that order.
Identify the assembly’s position and function in the single-line diagram.
Confirm voltage, frequency, earthing arrangement and applicable standard.
State continuous current, circuit count and calculated short-circuit level.
Choose the switching device, insulation approach and fixed or withdrawable structure.
Define protection, metering, interlocking, control and communications.
Confirm environment, layout, cable interfaces, tests and document scope.
Catalog ratings are reference data. The approved technical specification, system study and confirmed quotation govern the final equipment configuration.
| Input | What to Confirm | Why It Matters |
|---|---|---|
| System Conditions | Nominal and highest system voltage, frequency, earthing and applicable standard. | For a 35 kV-class system, selection is made within the 40.5 kV medium-voltage equipment range. |
| Continuous Current | Ratings for incomers, busbars, bus couplers and feeders, including future circuits. | Different circuits may require different continuous-current ratings and conductor arrangements. |
| Short-Circuit Duty | Calculated fault level and required duration. | Breaking, making, short-time and peak withstand duties must match the approved study. |
| Circuit Arrangement | Sources, transformers, bus sections, couplers, feeders, transfer logic and load types. | The SLD determines the panel lineup, functional units and operating sequence. |
| Switching & Construction | Circuit breaker, load switch, switch-fuse or other approved device; fixed or withdrawable construction. | The choice affects operation, isolation, maintenance and footprint. |
| Installation | Indoor/outdoor location, altitude, ambient conditions, room dimensions, access and cable entry. | Site data affects insulation, enclosure, ventilation, layout and interfaces. |
These functions should be defined with the circuit duty—not added after the primary equipment has already been selected.
Provide relay functions, trip logic and coordination requirements for every circuit. Final settings follow the project study and approved device list.
Define mechanical, electrical and key-interlock logic for breakers, isolating positions, earthing switches and access doors, including the required operating sequence.
Confirm CTs, VTs, meters, indication, control power, local and remote controls, alarms and communication interfaces.
For automated ring networks, state FTU requirements, remote indication and operation, distribution-automation functions and the communication interface.
Send the destination country, applicable standard, SLD, circuit schedule, system conditions, rated currents, fault level, switching functions, control voltage, automation requirements, site data and document requirements. Final drawings and schedules are reviewed after the configuration and scope are confirmed.
Send the destination country, single-line diagram, system voltage, fault level, circuit schedule, installation conditions and required documentation. We will review the duty and identify a suitable medium-voltage switchgear, RMU or low-voltage switchgear family.