When AC traction was introduced north of Virar, a small town at the end of Western Railway's 1.5 KV DC suburban section, it was necessary to establish a neutral zone to isolate 1.5 KV DC catenary from 25 KV AC catenary.
Based on technology and material available in 70s, a neutral zone spanned over three catenary structures. One section (between two catenary poles) had overlapping live and neutral wires, followed by a section with only a neutral wire, followed by third structure with overlapping live and neutral wires.
Although electrically fail-safe method, it offered a potential for stalled train being a dead duck. This was proved to be the case when a loco stopped under neutral wire due to emergency.
Move the clock forward. PTFE (poly-tetra-fluoro-ethylene) provided desired characteristics to isolate two different feeder circuits. Extruded PTFE rods are extremely rigid, less sensitive to temperature variations, offer lower coefficient of friction and extremely high electrical resistance.
Neutral zone at Virar isolates 1.5 KV DC and 15 KV AC circuits. Located less than 150 feet north of Level crossing, it was a significant achievement over the past technology.
This section, less than 15 feet long, equipped with two sets of gliders to let pantograph glide and PTFE rods isolates two different feeder circuits. Chances of stalled loco? Almost none. The center piece, some 4 feet long, is grounded by connecting it to catenary structure.