Underground hydro vaults like the one that exploded at 2 Secord Ave. trade off reliability in favour of safety and aesthetics, an official for Toronto Hydro said yesterday.
"From a reliability perspective, the overhead system is very reliable," said the company's vice-president of distribution grid management, Ben Lapianta. "The underground system is also reliable, but during storms, they are subjected to heavy rain waters ... and problems can arise."
The insulation on the cables running power in and out of the vaults is constantly being worn down by rainwater and street salt, said Lapianta, and this can lead to equipment failures and even fires and explosions, as seen in recent days.
Yesterday, hundreds of residents were left without power for most of the day after a fire in a vault near Bathurst St. and St. Clair Ave. W. The outage followed Sunday's explosion in a vault outside a Secord Ave. building which left 900 people homeless for at least four weeks.
Each of the 16,000 Toronto Hydro vaults in the city contains ventilation and drainage equipment, as well as temperature gauges to detect overheating. But with thousands of amps travelling through a room the size of a small swimming pool, problems will arise, many of which are caused by water or sudden surges in use, Lapianta said.
That's why, "if there is a defect, it's magnified in the summer," he said.
In the 50-year history of the vaults in North America, they've proven to be one of the safest, most reliable ways of keeping a city energized, said Peter Marcucci, vice-president of regulatory affairs for the Electrical Safety Authority yesterday.
Of the 1,431 power line-related mishaps in Ontario reported to the ESA between 2001 to mid-2007, a majority of them involved either overhead wires or above-ground green electrical boxes, he said.
