Hydro One’s technical analysis of the cause of the April 15 blackout in west Toronto has found that Toronto Hydro’s actions caused the event and that the event “represented a significant health and safety risk to utility workers and the public.”

The finding is contained in an industrial bulletin called “Clearance requirements between Hydro One transmission circuits and Local Distribution Company (LDC)/Customer equipment“. The bulletin was issued May 9. The report determined that inadequate clearance between a distribution pole line being constructed by Toronto Hydro and an existing overhead Hydro One transmission circuit resulted in a flashover.

Hydro One’s report notes that “Thankfully, no injuries resulted from the incident.” The report does not comment directly on the risk utility workers were exposed to at the time they were installing the Toronto Hydro line.

Hydro One’s report identifies the approvals Toronto Hydro was required to obtain from Hydro One prior to constructing the new distribution line (addressed in Part 110 of this series). Hydro One’s report informs Toronto Hydro of the correct procedures required.