The TTC says a cable chamber fire at Richmond and Victoria streets early this morning caused your nightmare TTC commute into the downtown core.

Vault fire

Toronto firefighters battle a blaze inside an underground hydro vault on Richmond Street early this morning. (Tony Smyth/CBC)

The fire is out, and subway and streetcar service has resumed after crews spent the morning repairing cables hit by the fire in the morning.

UndergroundFire

The fire broke out inside an underground hydro vault on Richmond Street near Church just after 1 a.m. (Tony Smyth/CBC)

Toronto firefighters discovered the fire when they responded to a carbon monoxide call at 50 Richmond St. E. just after 1 a.m. Crews then determined that it was an underground hydro vault on fire and hydro crews were called to the scene.

Firefighters

The hydro vault fire is the culprit for power problems that are causing widespread problems on the TTC this morning. (Tony Smyth/CBC)

TTC spokesman Brad Ross told CBC News that the underground hydro station is a "major source" of power for the TTC.

He says the Richmond substation feeds power to Line 1 between Dundas and Osgoode stations. It also feeds most of the downtown streetcar lines: Dundas, Queen, King, Spadina, Harbourfront,Wellington, Richmond, Adelaide, Bay, York, McCaul, Church, and Parliament.

That's why, when there's a fire in the chamber, all power has to be shut off to allow electrical crews to investigate and make repairs, said Ross.

Shuttle buses

The TTC has sent shuttle buses to move passengers between downtown subway stations. (Linda Ward/CBC)

Toronto Hydro said it has cables in the chamber but none of its equipment has been damaged. Spokeswoman Tori Gass said its workers were on scene to assist the TTC.  

What is a cable chamber?

According to Toronto Hydro, a cable chamber, which is the size of a small room, is an underground opening to the cable system.

Toronto Hydro Cable Chamber

A Toronto Hydro worker in a cable chamber similar to the one that caught fire early this morning paralysing streetcars and the subway. (Toronto Hydro)

Electrical cables that run under the sidewalks below ground are fed through large pipes called ducts.

At specific points throughout the city, the cables run into and out of a cable chamber providing an access point for repairs, inspections and new installations.

Toronto Hydro says there are about 10,000 cable chambers in the city.