Underground distribution maintenance in Korea means inspecting the operating condition of underground distribution lines to prevent unexpected faults, and repairing weak points and equipment that needs reinforcement in advance. Deterioration in underground equipment happens out of sight, so measuring at set intervals and building up assessment records is almost the whole of fault prevention. This guide covers two stages — inspection and maintenance.
Contents
- Common Pre-Work Review
- 1. Line Inspection
- Checks and Instruments by Equipment
- 2. Maintenance
- FAQ
- Reference Standards
- Summary
Common Pre-Work Review
Equipment covered includes switches, breakers, transformers, cables, control boxes and batteries, along with the manholes (handholes) and troughs that protect them. Reference values and normal conditions follow the maintenance guidelines or manuals. Prepare a combined relay tester, dielectric tester and protective relay tester, plus a phase meter, gas leak detector, insulation tester, thermal camera, earth resistance tester and ammeter, as well as a disconnect hot stick, earthing clamps, voltage detector, socket sets and contact cleaner. For manholes in roads, set out traffic signs, cones, beacons and barrier ropes.
1. Line Inspection
- Select inspection targets by interval and equipment type and carry out equipment and preventive inspections.
- Confirm inspection intervals and methods for the underground lines, inspect and assess compliance.
- Inspect cable deterioration and joint condition and assess compliance.
- Inspect cable terminations and surge arresters for deterioration and assess them.
- Check manual operation and batteries of distribution automation devices.
- Measure earth and insulation resistance for each piece of equipment and assess compliance.
- Measure toxic gases inside manholes and tunnels, and plan work-environment and safety improvements.
- Check distribution automation control boxes, batteries and breakers for defects.
- Measure contact resistance of switch or breaker contacts to detect defects.
Checks and Instruments by Equipment
| Equipment | Check | Instrument |
|---|---|---|
| Cables and joints | Deterioration, joint condition | Thermal camera, insulation tester |
| Terminations and arresters | Deterioration | Thermal camera |
| Switches and breakers | Contact resistance, operation | Contact resistance measurement, relay tester |
| Automation devices | Manual operation, control box, battery | Ammeter, visual check |
| Earthing and insulation | Earth and insulation resistance | Earth and insulation testers |
| Manholes and tunnels | Toxic gases, structural defects | Gas leak detector |
2. Maintenance
- Prepare a maintenance plan for underground distribution equipment.
- Replace lines and equipment according to the plan, based on inspection and assessment results.
- Operate replaced lines and equipment to confirm they work normally.
Maintenance is classified by purpose into preventive maintenance, corrective repair and improvement maintenance, and decided on reliability, suitability and usefulness.
FAQ
How is underground distribution maintenance classified?
By purpose: preventive maintenance to stop faults before they happen, corrective repair of failed parts, and improvement maintenance to raise performance.
How is cable deterioration checked?
Use a thermal camera to find abnormal heating at joints and terminations, and measure insulation resistance, assessing against the maintenance guidelines.
Why measure contact resistance?
Poor contact in switch and breaker contacts leads to heating and failure, so measuring contact resistance finds defects early.
Reference Standards
- Electricity Business Act (전기사업법) — law.go.kr
- Electrical Safety Management Act (전기안전관리법) — law.go.kr
- Electric Technology Management Act (전력기술관리법) — law.go.kr
- Electrical Construction Business Act (전기공사업법) — law.go.kr
- Occupational Safety and Health Act (산업안전보건법) — law.go.kr
- Korea Electro-technical Code (KEC, 한국전기설비규정) — law.go.kr
- KEPCO design standards; field practice manuals for transmission and distribution work; Korean Industrial Standards (KS)
- NCS competency unit Underground Distribution Maintenance (지중배전 유지보수, 1901070244_22v1; NCS is Korea’s National Competency Standards) — ncs.go.kr
Summary
The most common mistakes in underground distribution maintenance are recording results without assessing them, and skipping the operating check after replacement. Inspection depends on selecting targets by interval and measuring and assessing; maintenance on planned replacement and confirming operation. Installation standards are covered in Underground Distribution Cable Construction. For pre-construction preparation, see Distribution Line Construction Planning. A Korean version of this guide is available here.
This article restructures the Korean NCS competency unit ‘Underground Distribution Maintenance’ (지중배전 유지보수, code 1901070244_22v1) as a practical reference. Actual work must follow applicable standards and the judgment of qualified professionals; always confirm specific values, deadlines and criteria against the latest regulations and client standards.
Written/reviewed by VOLT · Last updated 2026-10-25