Enhanced Fujita scale damage indicators and degrees of damage, chapter 26

C-1 Electrical Transmission Lines (C-ETL)

Typical Construction:

• Single wood poles with wood cross arms, 7-35 metres (m) in height and 15-60 centimetres (cm) in diameter (at 2 m above ground)
• Single steel or concrete poles with metal cross arms
• Metal trussed towers

Notes:

• Whether poles go down is related to size, composition (wood / concrete / steel) and load (wire tension, number of transformers)
• For small diameter (~15-20 cm) or very old wood poles, decrease toward lower-bound wind speed; for large diameter (~45-60 cm) wood poles, increase toward upper-bound wind speed
• Keep in mind - one weak or overloaded pole going down can cause other poles along the line to break due to wire tension
• Trees falling on lines can bring down poles - do not use this DI if this is the case
• Metal truss towers where lines change direction are often more strongly reinforced, increase toward upper-bound wind speed

*All wind speeds in km/h