Terminology

AUTO RECLOSURE:  Refers to a momentary outage. This allows for clearance of what we call a transient fault caused by wildlife contact, lightning, branches, etc.

CABLE CHAMBER: A below-grade opening to the underground system that facilitates the installation and removal of feeders and provides access to cables requiring inspection and repair. They are located under sidewalks and roadways. Depending on location and construction type, life expectancy can range from 40 to 50 years.

CIRCUIT BREAKER: A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset to resume normal operation.

DISTRIBUTED GENERATION (DG), also DISTRIBUTED ENERGY (DE): On-site generation (OSG), or district/decentralized energy, is electrical generation and storage performed by a variety of small, grid-connected or distribution system-connected devices referred to as distributed energy resources (DER).

DISTRIBUTION SYSTEM: Is comprised of the wires, poles, transformers, substations and other equipment used to deliver electricity to customers. The distribution system delivers power at voltage levels that can be used in homes and businesses.

DISTRIBUTION TRANSFORMER: A large piece of equipment required to reduce the distribution voltage to secondary voltage to match customers’ appliances and equipment voltages.

ELECTRICAL GRID: An interconnected network for delivering electricity from suppliers to consumers.

FEEDER: 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.

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

HANDWELL: A small metal plate covering underground wiring for streetlights. These are usually located about 1 metre (3 to 4 feet) from an electrical pole. 

LIGHTNING ARRESTER: A protective device installed on the primary (high voltage) side of the distribution transformer. When a lightning surge (or switching surge, which is very similar) travels along the powerline to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth.

LOAD/CAPACITY GROWTH: Upgrading the existing system to handle new or existing customer loads or a higher connection capacity.

OUTSIDE UTILITY EQUIPMENT: Equipment (e.g. poles) that house similar parts, such as wiring, with other utilities (e.g. phone and cable companies)

OVERHEAD: Essentially a large diameter cable carrying power from a terminal or municipal station to customers using poles as supports.

POLES: Poles are constructed primarily of wood or concrete and provide support for all the overhead wires, switches and transformers throughout the city. Most poles are over 9 metres (30 feet) high and provide a safety barrier for the public.

RECLOSER: A recloser is an automatic high voltage electric switch. Like a circuit breaker on household electric lines, it shuts off electric power when trouble occurs, such as a short circuit. Where a household circuit breaker remains shut off until it is manually reset, a recloser automatically tests the electrical line to determine whether the trouble has been removed. If the problem was only temporary, the recloser automatically resets itself and restores the electric power.

SECONDARY CABLES (or Mains): Underground low voltage (<750 volt) cables which are connected to the secondary side (low voltage) of the distribution transformer and deliver the current to customers.

SUBSTATION: A subsidiary station where voltage is transformed from high to low or the reverse using transformers. In addition to transforming voltage, distribution substations also isolate faults in either the transmission or distribution systems. Distribution substations are typically the points of voltage regulation, although on long distribution circuits (of several miles/kilometers), voltage regulation equipment may also be installed along the line.

TRANSFORMER VAULT:  A transformer vault is a large room used to house submersible transformers, switches and protective equipment (fuses and surge arresters).  Transformer vaults can also be used to provide adequate working space for employees to install and remove equipment or conduct inspections and maintenance duties.

TREE TRIMMING: A preventive maintenance program that cuts back trees to prevent branches from damaging or blowing into overhead lines and causing outages.

UNDERGROUND CABLE: Cable manufactured without an outer protective layer of polyethylene and buried without any form of casing. Cables have a life expectancy of approximately 25 to 40 years.