Manhole connector caused massive Vancouver power outage

But the independent report exonerated the utility, saying its underground inspection procedures are "prudent" and the "design, operation, inspection and replacement regime for the BC Hydro feeder cable systems meet or exceed industry norms."

The 39-page report, by Powertech Labs Inc., concluded that the power outage the morning of July 14, which left more than 2,000 downtown Vancouver customers in the dark, was caused by an overheated connector in a manhole.

An investigation concluded that the resulting fire and explosion led 13 other circuits in the manhole to fail, the report said.

It noted that in 2004, BC Hydro began a new assessment program which involved selecting circuits for inspection based on age, the importance of the circuit and other criteria.

It was during an inspection in January, 2008, of the connector that caught fire six months later that BC Hydro discovered a temperature difference of 5.3 C between the connector and the cable connected to it.

The connector was assigned a Level 4 priority, which is Hydro's highest priority rating except for situations requiring immediate attention for safety reasons.

"BC Hydro did not take immediate action to repair this connector, which eventually failed on July 14, 2008," the report said.

BC Hydro says that while underground circuit failures are not uncommon, the connector that failed was only three years old and the components usually have a lifespan of at least 30 years.

As a result, the utility has implemented several changes, including the creation of a BC Hydro fire marshal position, improving training with the Vancouver Fire Department and a program to inspect connectors similar to the one that led to the blackout.