Home » English riddles » Protection » Protection Riddle No.81 – Frequency of surges and impulses » Reply To: Protection Riddle No.81 – Frequency of surges and impulses Reply To: Protection Riddle No.81 – Frequency of surges and impulses 2021-08-03 at 11:08 am #2375 Hamid From measurements made on communication lines and on utility power lines, both outside and within structures,