1. General & Installation Criteria
All works
must follow the mutually inclusive Technical Specifications and Construction
Standards of the Nepal Electricity Authority (NEA) (2007 February). Line
alignments must be as straight as possible to minimize stays.
Basic
spans are set at 50–55m for 33 kV and 11 kV lines, and 35–50m for low voltage
(LV) lines depending on the wire count. Prior to installation, old wooden poles
must be dismantled.
Line
clearances, optimum conductor sag, and safety rules must be strictly
maintained. Break angles dictate whether HV pin insulators or disc insulator
fittings (for dead ends) are used.
2. Stays & Transformer Structures
At least
one stay must be installed for dead-end and tee-off structures, unless specific
pole, span, and break-angle conditions remove the requirement. Transformer
structures require two separate earth rods driven at least 2m from the pole and
separated by 6m.
One rod
grounds surge arresters/equipment, while the other grounds the low-voltage
winding neutral, transformer body, and MCCB box. Copper circuit conductors must
be placed below aluminum conductors to manage rainwater flow.
Transformers
can only be charged after the Transformer Commissioning Report is approved.
3. Grounding Procedure
Grounding
is mandatory for surge arrester studs, non-current carrying parts, and LV
neutral points. The LV line neutral must be grounded every 15 poles. Specific
conductor sizes are mandated (e.g., 2 AWG copper welded for surge arresters)
and must be encased in rigid plastic pipes 3m above the pole foundation. Ground
rods must be driven at least 40cm below grade.
4. Low Voltage Circuits & Miscellaneous
Works
Bare
400/230V circuits utilize shackle insulators with D-irons, mounted on the side
facing most house connections. Conductors require a 305mm spacing, arranged
vertically from top to bottom as Red, Yellow, Blue, and Neutral.
Conductor stringing includes required fittings, with double disc insulators placed at extreme deviations. Tree trimming must be coordinated with the CBO, and all dismantled structures must be transported back to the site store.
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