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Developed and maintained
by the NFCC

Transmission towers (pylons) and wooden poles


Transmission overhead lines at 400kV or 275kV are supported on large galvanised steel towers and consist of uninsulated aluminium/steel or aluminium alloy stranded conductors. The conductors are insulated from the tower by porcelain or glass insulators.


Figure 11: Transmission tower - photograph courtesy of Peter Martin

Most towers carry two circuits, with the three phases of each circuit installed in a vertical form on opposite sides of the tower. An additional conductor, which is an earth wire, connects the peaks of the towers together. Depending on the power transfer of each circuit, the phases may have single, twin or quadruple sub-conductors.

Each tower has a unique identification number, which is displayed on a notice mounted above an anti-climbing guard, installed to prevent unauthorised access to the upper sections of the tower.

Each circuit has a unique circuit identification, which is a combination of colours or symbols; these are displayed on the plates fixed at various points on the legs of the tower.

Wooden poles operate from low voltage through to 132kV (high voltage). Only high-voltage poles are fitted with danger notices.

Hazards (for further information refer to National Operational Guidance: Utilities and fuel)

  • High risk of electrocution
  • Working at height

References and further reading