BS 6485 covers hard-drawn conductors with an extruded PVC covering for use on overhead power lines. The covering is not full insulation; it is a protective layer that greatly reduces faults from branches brushing the line, birds and accidental contact with tools or scaffolding. The standard defines two types by the line voltage they may be used on, with Type 8 for low voltage work and Type 16 for lines operating above 650 V up to 11 kV.
Key applications
- Overhead distribution lines running close to trees
- Spans near buildings, scaffolding or site access routes
- Replacement of bare conductor on fault-prone rural spans
- Lines crossing areas with heavy bird activity
- Short overhead spans on industrial and agricultural sites
- Service connections where clearances are tight
Features and benefits
- PVC covering sharply reduces outages from vegetation and incidental contact
- Allows reduced phase spacing compared with bare conductor
- Two voltage types cover both LV and up to 11 kV applications
- Colour convention of green for HV and black for LV aids identification on site
Specification notes and limitations
The single most important point is that covered conductor is not insulated conductor. The PVC covering is not rated to withstand system voltage to earth and gives no protection to anyone who touches the line — the conductor must be treated as bare and live, with full statutory clearances and approach distances maintained. The covering reduces the consequence of momentary vegetation contact; it does not permit the line to rest on a tree. Covered conductor is also prone to localised burning at a persistent fault point rather than clearing the fault the way bare conductor does, so fault detection arrangements need thinking about. The reduced spacing permitted by the covering does not relax ground clearance or crossing requirements, and the PVC will chalk and degrade over many years of UV exposure.
