NOTE: If CRL Is < 1000, protection against transients is required


FENV = environmental factor from table 443.1

Lp = risk assessment length

Ng = lightning ground flash density fron figures 44.2

Lp = 2 Lpal + 0.4 Lpah + 0.2 Lpch

Lpal = length in KM of lv overhaed supply


  1. Select either 'RURAL & SUB' or 'URBAN'
  2. Enter a value in 'Ng' (Lightning ground flash density from figures 44.2) This must be greater than 0 but less than 2
  3. Enter a value in at least one of the four fields 'Lpal', 'Lpcl', 'Lpah' or 'Lpch'. Value(s) must be greater than zero and no more than 1.
  4. Click the big red button at the bottom right to do the calculation
  5. If you would like to do another calculation, click the 'CLR' button to clear all the current data