--- title: "Aerial bundled conductor in LT distribution" subject: "Transmission and Distribution System Design" chapter: 7 key: "semester_8/transmission_and_distribution_system_design:abc-lt-distribution" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/abc-lt-distribution site: BCT Engineering --- # Aerial bundled conductor in LT distribution Transmission and Distribution System Design · Chapter 7: Distribution System Design - Asked in: 2078 Kartik, 4 marks; 2071 Magh, 8 marks; 2070 Magh, 6 marks; 2069 Bhadra (old course), 4 marks; 2068 Bhadra (old course), 6 marks (asked 5 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/abc-lt-distribution - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-7 ## Question What is aerial bundled conductor (ABC)? Discuss the advantages and disadvantages of ABC in LT distribution. ## Short answer ABC is an overhead line with XLPE-insulated phase conductors twisted around a bare or insulated messenger, hanging from poles without cross-arms. Advantages: improved safety, reduced theft, fewer faults from trees/birds, lower reactance, and easier installation. Disadvantages: higher initial cost, lower ampacity, heavier bundle, and difficult fault location. ## Answer **Aerial bundled conductor (ABC)** is an overhead LT (or HT) line in which the phase conductors, and usually an insulated or bare neutral messenger, are each covered with XLPE (cross-linked polyethylene) insulation and twisted together into a single bundle. The bundle hangs from the poles by its messenger (neutral) wire using suspension and dead-end clamps, instead of bare conductors on cross-arms and pin insulators. ```text Bare LT line ABC LT line o o o o (bundle on one clamp) --------------------- _____ | cross-arm | / R Y \ | | | B N | XLPE | pole | \_____/ insulated | pole ``` A typical LT ABC is 3 × 95 mm² + 1 × 70 mm² (messenger) + 1 × 16 mm² (street light), aluminium. #### Advantages - **Safety:** the conductors are insulated, so there is little risk of electrocution from accidental contact; this makes ABC safer in crowded urban areas. - **Reduced theft (pilferage):** direct hooking ("katiya"), which is easy on bare lines, is very hard on ABC. This cuts non-technical losses, a major issue in Nepal. - **Higher reliability:** no faults from tree branches, birds, kites or wind-driven clashing of conductors, so there are fewer outages. - **Less right-of-way and clearance:** no cross-arms are needed; the line can run close to buildings and through trees, with less tree trimming. - **Lower reactance:** the conductors are close together, so the reactance (~0.1 Ω/km vs ~0.3 Ω/km) and the voltage drop are lower. - **Easy installation:** fewer accessories (no cross-arms or pin insulators), poles can be shorter, and the line is quick to string. - **Better appearance** and lower maintenance cost. #### Disadvantages - **Higher initial cost** of conductor (about 1.5–2 times that of bare conductor). - **Lower current rating** for the same size, because the insulation reduces heat dissipation. - **Heavier** bundle, needing stronger poles or shorter spans. - **Fault location is difficult** since the conductors are covered; insulation damage may not be visible. - **Tapping of service connections** needs special insulation-piercing connectors. - Poor-quality XLPE insulation **ages** under ultraviolet light and heat. - Repair and jointing need trained staff and special tools. | Aspect | Bare conductor | ABC | |---|---|---| | Cost | Low | High | | Safety | Poor | Good | | Theft | Easy | Difficult | | Reactance | ~0.3 Ω/km | ~0.1 Ω/km | | Faults from trees | Frequent | Rare | ABC is now widely used by NEA for LT distribution in urban and loss-prone areas. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Aerial bundled conductor is: A. Bare conductors on cross-arms B. Insulated (XLPE) phase conductors twisted into one bundle hung from a messenger C. An underground cable D. A single bare wire with earth return Answer: B. ABC uses XLPE-covered conductors twisted together and supported by the messenger wire. (Key point: What is ABC) 2. Which is an advantage of ABC in Nepal? A. Cheaper conductor B. Higher current rating C. Hooking (katiya) is difficult, reducing theft, and tree/bird faults are rare D. Easy fault location Answer: C. Insulation prevents direct hooking and contact faults, cutting non-technical losses and outages. (Key point: Reduced pilferage and faults) 3. Why is the voltage drop lower in ABC than in bare lines? A. Resistance is lower B. Conductors are close together so reactance is lower (~0.1 vs ~0.3 ohm/km) C. Voltage is higher D. It has no neutral Answer: B. Close spacing of the bundled conductors cuts reactance. (Key point: Electrical advantage) 4. Why does ABC have a lower current rating than a bare conductor of the same size? A. It is thinner B. Insulation reduces heat dissipation C. XLPE has high resistance D. The messenger carries current Answer: B. The insulation traps heat; other drawbacks are higher cost, weight and difficult fault location. (Key point: Disadvantage) ## Related in Transmission and Distribution System Design - [Distribution loss and voltage drop, four LT feeders](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aload-center-40kw-four-lt-feeders) — Transmission and Distribution System Design, chapter 7 - [LT feeder options: loss and voltage drop, 50 kW](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Alt-feeder-two-options-50kw) — Transmission and Distribution System Design, chapter 7, asked 3× - [LT loss and voltage drop, 60 kW four feeders](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Alt-feeders-60kw-1-5km-380v) — Transmission and Distribution System Design, chapter 7, asked 3× - [Peak loss and voltage drop for LT feeder options](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Alt-feeder-configuration-options) — Transmission and Distribution System Design, chapter 7, asked 2× - [LT loss and voltage drop, four 2 km feeders](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Alt-feeders-40kw-2km-380v) — Transmission and Distribution System Design, chapter 7, asked 2× - [Electrical considerations in conductor selection](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aconductor-electrical-considerations) — Transmission and Distribution System Design, chapter 4, asked 3× ## Related in other subjects - [Inductance of 3-conductor bundled line, 6.1 m spacing](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ainductance-three-subconductor-bundle-6-1m) — Power System Analysis I, chapter 4 - [Capacitance matrix of 400 kV bundled line](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Acapacitance-matrix-400kv-15m) — High Voltage Engineering, chapter 5, asked 2× - [Stranded and bundled conductors; bundling in EHV](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Astranded-bundled-ehv) — Power System Analysis I, chapter 2 - [Effect of bundled conductors on L and C](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Abundled-conductor-effect-l-c) — Power System Analysis I, chapter 4