Usually, people hit wires because they don't know they are there and that is where WSP is useful - the National Grid guys on the other hand know exactly where the wires are since they are surveying them - why add WSP for that?
A fair assumption you would think. But apparently not so.
One thing is certain: wire strikes are not a rookie mistake. Information drawn from Civil Wire Strike Assessments by the National Aeronautics and Space Administration (NASA) indicate that the average wire strike pilot is 40 years old with 2,300 hours of flight experience. 86% of wire strikes happen in clear weather with good visibility, and 40% of the pilots who hit wires knew before the accident that they were there.
Source
I know of at least 3 serious accidents in just this same role. The HV ones are easy. Its the Network Provider ones that the National Grid doesn't own that can be a problem.
All LV crossings of HV are now marked on the tower in Australia for example.
While concentrating on the HV you run into the LV.
For me WSPS is a must have. Weight is the only penalty. Money is not the issue.
PS - The pic of the AS350 doing the "sock" line job is a fairly good example of possibly how NOT to do it. A "headache" ball and a long line is the better way.