Great big grate

>> What lurks beneath that sidewalk cage?

By PHILIP PREVILLE

The most famous sidewalk grate of all time is, beyond a shadow of a doubt, the one Marilyn Monroe stood atop in The Seven Year Itch, sending aflutter both her pleated white dress and the hearts of infrastructure buffs everywhere. Mind you, Norma Jeane's grate was a subway vent. Montreal has few such vents for the metro, and they are never located at street level.

What you find more often in this town are the sidewalk grates that appear in film noir. You know the kind: the brooding grates that let off a steady flow of steam into the dark, rainy, nighttime city streets, like the breath of a monster caged beneath the surface.

Alas, there's no creature to be found down there. The grates lead to special manholes called transformer vaults, and the steam comes from the equipment installed there by Hydro-Québec.



The vault: Beneath the sidewalk cage lies a concrete room, eight metres long, three metres wide and three metres high. In Montreal, the vaults are built exclusively by the Montreal Electrical Services Commission, and though it's just a simple concrete box, it still costs about $100,000 to build. The MESC actually owns the vaults, along with all the underground cable conduits. They rent out the cable conduits to such clients as Bell and Vidéotron. They rent all the vaults--2,400 of them in all--to Hydro-Québec.



The equipment: Inside the vaults, transformers convert 25,000-volt high-tension electric wires into a whole bunch of 120-volt lines, which in turn lead in to surrounding homes and businesses. Most vaults contain two transformers, which look like big metal cubes, valued at about $200,000 each. In other words, beneath that grate lies a hole in the ground worth half-a-million bucks. "We're trying to move as many transformers as possible underground," says Hydro-Québec engineer Gilles Desjardins. "We can install higher-capacity transformers in the vaults, and they're not pretty so we're happy to bury them. But it's still much cheaper to put them up on poles." Neighbourhoods with the poles shouldn't hold out hope that their wires and transformers will be buried anytime soon.



The grate: Isn't it dangerous to have electrical equipment beneath a grate that doesn't keep out the rainwater? No. "All the transformers in the vaults are fully submersible," explains Desjardins. "They can function even when they're completely underwater. And some of them are underwater, because some of the vaults are located right next to massive leaks in the city's water distribution pipes."

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