The bypass cable method in Korea connects the source and load sides of the work section with a bypass cable to keep power flowing, then separates the work section’s jumpers by live-line work so the section can be worked dead. Unlike the temporary switch method, customers inside the work section stay supplied, which makes the cable connection and phase-check sequence longer and more exacting. This guide covers two stages — preparation and execution.
Contents
- Common Pre-Work Review
- 1. Preparation
- 2. Execution
- Bypass Connection and Restoration Sequence
- FAQ
- Reference Standards
- Summary
Common Pre-Work Review
This method applies to 22.9 kV-Y and below overhead distribution lines when work is done without de-energizing the line. Prepare an insulation resistance tester, HV ammeter, HV and LV phase meters and HV voltage detector, plus an insulated aerial device; a mobile temporary switch as no-outage equipment; and hand tools such as nippers and screwdrivers. Workers wear hard hats, safety vests, safety shoes, insulating gloves and harnesses, with line and insulator covers ready. Materials include sleeves, lugs and insulating tapes.
1. Preparation
- Prepare the site: pedestrian route, traffic marshals, earthing of equipment and vehicles, wheel chocks and load current measurement.
- Hold a safety meeting covering task assignment, PPE, equipment and line checks and risk assessment.
- Notify the distribution center, cover live parts and send site monitoring data for no-outage work.
On arrival, review traffic, pole-top configuration and buried services and carry out hazard prediction training; control traffic and pedestrians with barrier ropes, signs and marshals. Before no-outage work, notify the distribution center and confirm auto-reclosing is blocked; notify completion afterwards.
2. Execution
- Test the work section for voltage and apply short-circuit earthing.
- Cover the neutral and install temporary switches as the procedure requires, then, following the supervisor and watching live and dead sections, carry out dead work such as new or relocated conductors, pole-top changes, new or relocated poles and equipment installation or removal.
- After the dead work, remove the temporary switches in reverse order to restore normal service.
- Notify the distribution center of completion and tidy the site to avoid complaints.
Bypass Connection and Restoration Sequence
| Stage | Sequence |
|---|---|
| Build bypass | Measure load current, cover neutral, send monitoring → install temporary switches, intermediate cable, auxiliary stands and riser clamps → install and check HV risers |
| Convert to dead | Connect risers at switch pole → phase check and close temporary switch → connect risers on branch line → cut jumpers → open pole transformer COS |
| Restore | Remove short-circuit earths → phase check and reconnect jumpers → open source- and load-side temporary switches → disconnect, discharge and remove risers → remove covers |
This sequence summarizes the NCS considerations; actual work follows KEPCO standard procedures and the site supervisor.
FAQ
What is dead-section work?
Work done after converting only the work section to a de-energized (dead) state, while the surrounding line and customers stay supplied, so the job needs no outage.
How does the bypass cable method differ from the temporary switch method?
The temporary switch method needs a section with no customers; the bypass method supplies the load through a bypass cable, so work can proceed without an outage even with customers in the section.
Why test for voltage and apply short-circuit earths before dead work?
To eliminate any residual or back-fed voltage in the separated section and protect workers.
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 Bypass Cable Method for No-Outage Work (바이패스케이블공법 공사, 1901070240_22v3; NCS is Korea’s National Competency Standards) — ncs.go.kr
Summary
The most common mistakes with the bypass method are skipping the phase check after building the bypass and omitting voltage testing and earthing of the dead section. Preparation depends on covering and monitoring; execution on the sequence build bypass → convert to dead → dead work; and restoration on phase-checked jumper reconnection and cable discharge. 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 ‘Bypass Cable Method for No-Outage Work’ (바이패스케이블공법 공사, code 1901070240_22v3) 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