Clearances for 9kV electric fields
The UK public exposure limits for electric fields is 9 kV/m. National Grid design its overhead lines to comply with this limits. Below are the required minimum conductor clearances for the current overhead lines designs used.
The field depends on several factors as shown in the table: the tower design, the conductor bundle, and the phasing (transposed, T, or untransposed, U - other phasings lie between these values). This information should be using in conjunction with National Grid’s Policy Statement PS(T) 103. If tower designs or phasings not included in the table are considered, please contact the EMF team for further information on [email protected].
| Line voltage | Tower construction | Conductor system | Bundle spacing | Clearance to achieve 9 kV/m | |
| T | U | ||||
| 275/400kV | L2 | 2 x 400 ACSR | 400mm | 7.3 m | 8.5 m |
| L2/1 | 2 x 500 ACSR | 7.4m | 8.6m | ||
| L2/2 | 2 x 500 AAAC | 7.4m | 8.6m | ||
| L2/3 | 2 x 425 AAAC | 7.4m | 8.6m | ||
| L2/4 | 2 x 570 AAAC | 7.4m | 8.6m | ||
| L2/6 | 2 x 620 GTZACSR | 7.4m | 8.6m | ||
| L2/7 | 2 x 591 ACC | 7.4m | 8.6m | ||
| L2/8 | 2 x 780 ACC | 7.4m | 8.6m | ||
| 275kV | L3 | 2 x 175 ACSR | 400mm | * | * |
| L3/1 | 1 x 700 AAAC | * | * | ||
| L3/2 | 2 x 300 AAAC | 300mm | * | * | |
| 275kV | L34 | 2 x 175 ACSR | 400mm | * | * |
| 132kV | L4(M) | 1 x 175 ACSR | * | * | |
| 275/400kV | L6 | 4 x 400 ACSR | 500mm | 8.9m | 9.9m |
| L6/1 | 2 x 400 ACSR | 400mm | 7.8m | 8.3m | |
| L6/2 | 2 x 700 AAAC | 500mm | 8.0m | 8.6m | |
| L6/3 | 2 x 500 AAAC | 400mm | 7.8m | 8.3m | |
| L6/4 | 2 x 850 AAAC | 550mm | 8.1m | 8.8m | |
| L6/5 | 3 x 700 AAAC | 500mm | 8.5m | 9.3m | |
| L6/6 | 2 X 570 AAAC | 400mm | 7.8m | 8.4m | |
| 275kV | L66 | 2 x 175 ACSR | * | * | |
| L66/1 | 1 x 700 AAAC | 300mm | * | * | |
| L66/2 | 2 x 300 AAAC | * | * | ||
| 132kV | L7(C)/1 | 1 x 400 ACSR | 300mm | * | * |
| L7(C)/2 | 2 x 400 ACSR | * | * | ||
| 275/400kV | L8 | 2 x 400 ACSR | 400mm | 7.5m | 8.4m |
| L8/1 | 2 x 500 ACAR | 7.5m | 8.5m | ||
| L8/2 | 2 x 500 AAAC | 7.5m | 8.5m | ||
| L8/3 | 2 x 425 AAAC | 7.5m | 8.4m | ||
| L8/4 | 2 x 570 AAAC | 7.6m | 8.5m | ||
| L8/6 | 2 x 620 GTZACSR | 7.5m | 8.5m | ||
| L8/7 | 2 x 591 ACC | 7.5m | 8.6m | ||
| L8/8 | 2 x 780 ACC | 7.6m | 8.5m | ||
| L9 | 4 x 400 ACSR | 500mm | 8.0m | 8.9m | |
| L12 | 2 x 700 AAAC | 7.8m | 8.8m | ||
| L12/1 | 2 x 850 AAAC | 550mm | 8.0m | 8.9m | |
| L13 | 3 x 700 AAAC | 500mm | 8.4m | 9.3m | |
* Minimum clearance to ground will apply