Aerial bundled conductor in LT distribution

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.

   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.

ABC is now widely used by NEA for LT distribution in urban and loss-prone areas.