Ring main units need low maintenance. However, “low maintenance” is not the same as “no maintenance”. A structured inspection and testing program keeps an RMU reliable for decades. It also prevents unplanned outages and keeps maintenance staff safe. This guide covers the essential maintenance practices for RMUs.

1. Why Ring Main Unit Maintenance Matters

An RMU protects people and equipment. If an earthing switch fails to close, the consequences can be severe. If someone bypasses an interlock, the risk grows. Regular inspection catches small problems early. Moisture ingress, corroded contacts and low gas pressure all show up first in inspections.

2. Routine Inspection Checklist

• Check enclosure integrity: doors, gaskets and cable entries for signs of moisture, dust or corrosion
• Inspect the operating mechanism and indicators: switching position displays should match the actual state
• Verify earthing switch operation and the correct sequence of interlocks
• For SF6 gas-insulated units, check the gas pressure gauge and monitor for leaks
• Look for signs of overheating: discolored busbars, melted cable insulation or unusual odors
• Check cable terminations and connections for tightness and signs of discharge
• Verify the control circuit, if fitted, including auxiliary contacts and heaters

For fixed-type air-insulated units such as the GSM6-12~24 Air-insulated RMU, no gas checks are needed. Maintenance focuses on cleanliness and mechanism operation.

3. Testing and Commissioning

1. Measure contact resistance on load break switches and circuit breakers
2. Perform mechanical operation tests including close-open cycles
3. Test interlocks and earthing switch operation with the door closed
4. Where permitted, perform insulation resistance tests on the cable circuits
5. Verify protection settings and trip signals if relays or VCBs are installed

4. SF6 Gas Management

For SF6 units, maintain the pressure within the manufacturer’s range. Leakage is a reliability and environmental issue. SF6 has a very high global warming potential. Sealed designs such as the GSRM6 Gas Insulated Ring Main Unit reduce this risk. However, pressure checks should still be part of the inspection cycle.

Suggested Schedule

Inspect visually every 6 to 12 months for indoor units. Dusty or coastal sites need more frequent checks. Test mechanisms and earthing switches at least once a year. SF6 pressure checks follow the manufacturer’s interval. Sealed units typically need these every 3 to 5 years. Keep a log of every inspection. This way, trends such as rising contact resistance become visible early. You can then fix them before they cause an outage.

Keep a small stock of consumables on site. This includes operating handles, indicator labels, fuse links and spare control fuses. Fast replacement of these items avoids extended downtime during the maintenance window.

5. Safety Rules for Maintenance

• Always isolate and earth the unit before opening any compartment
• Never defeat interlocks to speed up a job
• Use the correct personal protective equipment, including arc-rated clothing where required
• Follow the manufacturer’s operating sequence and document every operation

In practice, a well-documented maintenance program is also a procurement advantage. It proves to insurers and utilities that the equipment is operated responsibly. Many operators share these records during audits or warranty claims. Start the program from day one. Even simple records, such as photographs of the panel at each visit, become valuable evidence over time.

6. Conclusion

Good maintenance extends RMU life, improves safety and reduces outage costs. Build the checks above into an annual or bi-annual program. Record the results every time. For outdoor RMU applications, take a look at the Outdoor ring main unit.

Electric-GS is a professional power and electrical equipment manufacturer in Yueqing, Zhejiang, China. The company produces air-insulated, SF6 and solid-insulated ring main units. OEM and ODM support is available. For spare parts or technical support, contact info@electricgs.com or WhatsApp +86 135 8897 8050.

Related Products

GSM6-12~24 Air-insulated RMU (Fixed Type)

GSRM6 Gas Insulated Ring Main Unit

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