RMU & Recloser Hub

An RMU (Ring Main Unit) is a compact MV switchgear arrangement used for ring networks or compact substations where space, modularity, and switching convenience matter. It’s typically selected for secondary distribution with standardized incoming/outgoing feeders. If your project needs frequent feeder automation, advanced protection, or larger fault interruption duties, the “RMU + breaker / protection relay” approach becomes more relevant.

Use RMU + fuse when you want a simple, cost-effective transformer protection strategy and accept single-shot operation and fuse replacement after fault clearing. Use RMU + breaker when you need protection coordination, reclose capability, selective tripping, or operational flexibility. The right answer depends on fault levels, protection philosophy, outage tolerance, and maintenance capability.

A recloser is designed for feeder protection + automation, clearing temporary faults and restoring service via controlled reclose sequences. It is not a replacement for every circuit breaker role inside a substation lineup. Where isolation, high interrupting duties, or complex interlocking is needed, a breaker-based scheme may be more appropriate.

A recloser provides protection and reclosing; a breaker is a broader protection/interrupting platform used across substations and switchgear lineups; a sectionalizer relies on upstream interruption and is mainly for segmentation and reliability improvement. Confusion usually happens when people try to “make a sectionalizer behave like a recloser” or choose a recloser where a substation breaker is required. Use the device-role comparison to prevent misapplication.

The biggest mistakes are: setting curves that don’t coordinate with upstream/downstream devices, choosing sequences that create nuisance outages, and ignoring load growth or fault-current reality. Another common issue is copying a “template setting” without validating feeder type (overhead vs underground), grounding, and protection objectives. Use the settings guide as the baseline, then validate with your coordination study.

An LBS is primarily for load switching and controlled switching operations—its interrupting capabilities depend on the ratings and the design standard. It is not the same as a circuit breaker for clearing high short-circuit currents. In RMUs, the protection strategy often pairs LBS with fuses or other protection schemes—use the LBS guide to map “what it can do” vs “what your network needs.”

Selection is driven by project policy, maintenance practices, lifecycle considerations, and the available RMU architecture in your market. Alternatives may reduce SF6 handling requirements or shift tradeoffs into insulation system design and serviceability. The practical approach is to start from system duty and procurement constraints, then pick the architecture your supply chain can support reliably.

For RMUs: ask about configuration options (LBS/fuse/breaker), interface standards, testing documentation, service access, and spare parts. For reclosers: ask about control features, settings/curves support, communications, testing records, and field service references. Use the two manufacturer shortlists as your checklist backbone.