http://www.legislation.gov.uk/nisr/2012/381/section/21/madeTHE ELECTRICITY SAFETY, QUALITY AND CONTINUITY REGULATIONS (NORTHERN IRELAND) 2012Dangerous animalsElectrical installation and servicingenGovernment Printer for Northern Ireland2014-10-07ELECTRICITYThese Regulations replace the Electricity Supply Regulations (Northern Ireland) 1991 (S.R. 1991 No. 536) and the subsequent amendment (S.R. 1993/21).PART 5OVERHEAD LINES

Avoidance of interference with or interruption of supply caused by trees21.

A generator or distributor shall, so far as is reasonably practicable, ensure that there is no interference with or interruption of supply caused by an insufficient clearance between any of their overhead lines and a tree or other vegetation.