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As of Dec. 31, 2017

Note: numbers are approximate

City of Toronto population
Total number of customers
Electricity Delivered (GigaWatt-Hours)
Distribution Revenue and Other Revenue

Peak Load - September 26, 2017
Control Centre

2.8 Million
$831.9 Million

4,316 MW


Length of overhead wires (km)
Length of underground wires (km)
Primary Switches
Distribution Transformers





(Source: Independent Electricity System Operator)


 ELECTRICITY GLOSSARY                                                                                                                                             

Arcing (gapping)
The flow of electricity through the air from a conductor to another object that conducts electricity. Produces visible flashes and flames and a crackling sound.

Arrester (surge, lightning)
A protective device installed on the primary (high voltage) side of the distribution transformer. It's used to prevent excessive over-voltage surges across the transformer, caused by lightning strikes or live-line switching.

A rigid, large conductor, usually used in substations, to provide a quick, convenient means of rearranging circuit connections to keep power flowing or to restore power in case of equipment damage.

Cable Chamber
A below-grade opening to the underground duct system which facilitates the installation and removal of cables, and provides access to cables requiring inspections and repair, and for making cable splices and joints.

Cable Fault
A hole in a cable caused by a short circuit (due to corrosion, overloading over time, water, age) which can result in an explosion. Faults can occur at joints in cable chambers or in ducts between the chambers. Crews use "fault finding equipment" to locate and repair underground cable faults.

Installed in substations and on poles to help improve the efficiency of lines to carry electrical power by reducing energy losses.

A continuous system of conductors providing a path for electricity.

Circuit Breaker
An overcurrent protective switch in a substation that automatically disconnects power to the circuit in the event of a fault condition. Performs the same function as a circuit breaker in a home.

Current Limiting Fuse
A device that limits the amount of fault current flowing into the fault.

Cutout (or Fused Cutout)
A protective device installed on the primary side of the distribution transformer. It's used to prevent short-circuit currents from damaging the transformer itself or the secondary lines that are connected to the low-voltage side of the transformer. Cutouts are also used as switches to isolate the transformer or a single-line primary run-off to effect repairs on them.

Distribution Transformer
A large piece of equipment required for reducing the distribution primary voltage to the secondary voltage, thereby matching the customers' appliances and equipment voltages.

Used to terminate cables in vaults and in padmounted transformers. They can come in loadbreak and in deadbreak types.

A distribution circuit carrying power from a substation. The heavy high-voltage cable (circuit) supplies the distribution transformers and emanates from the station via ducts beneath city streets to the designated service areas.


Feeder Lockout

The main circuit is interrupted at the substation by automatic protective devices and cannot be restored until crews investigate. Usually indicates a serious problem on the circuit, either a broken conductor or other equipment failure.

Protects the distribution line from overloading. Acts by melting during overloading or faults, breaking the circuit. Is similar to fuses found in fuse boxes in homes.

When one or more conductors contact the earth, causing the electricity to flow out of the circuit into the earth.

Low-voltage fusible devices connected to each end of a secondary cable run. Their purpose is to prevent excessive cable damage and possible chamber fires caused by sustained secondary cable faults.

Equals 1,000 kilowatts or enough to power 10,000 100-watt light bulbs.

Used mostly to terminate paper-insulated lead-covered cable.

An assembly of components that enables the underground feeder cables to emerge from below grade and be brought up a pole for connection to the overhead lines.

Secondary Cables (or Mains)
Underground low voltage ( <750 volt) cables which are connected to the secondary side (low voltage) of the distribution transformer and delivers the current to customers.

A device for isolating a piece of equipment or a section of feeder to allow repairs or replacements to be made on them while in a de-energized state.

A device used to transform voltage levels to facilitate the transfer of power from the generating plant to the customer. A step-up transformer increases the voltage while a step-down transformer decreases it.

Transformer Vault
A large room of either the walk-in or the below-grade type and serve the following purposes: (1) houses submersible transformers, switches and protective equipment (fuses and surge arresters), and (2) provides adequate working space for personnel to install and remove equipment and to effect various inspections and maintenance duties

Tree Wire
A covered conductor used in heavily treed areas to provide some protection from momentary tree limb contact.

A measure of the work electricity can do.
1000 watts = 1 kilowatt
1000 watts = 10 100-watt light bulbs
1000 kilowatts = 1 megawatt