Oncor Logo
Report Outage Icon Menu Arrow

Report Outages

Streetlight Icon Menu Arrow

Report Streetlight Outages

Outage Map Icon Menu Arrow

View Outage Map

Signal Icon Menu Arrow

My Oncor Alerts

Phone Icon Menu Arrow

Service Requests

Question Mark Icon Menu Arrow

Ask Oncor

English (United States)

Featured Video

Common Utility Terms

Circuit Breaker - An electrical device that interrupts the flow of current when it exceeds a predetermined value. A circuit breaker is used to energize or de-energize a circuit and can be programmed or set up with various protection schemes to minimize damage to lines and equipment and to minimize dangers to the general public. Circuit breakers may be programmed to attempt several closes before it locks open in attempts to clear a fault from a circuit without a permanent interruption in the flow of power. The result is that power may go off and on several times in quick succession before it is completely interrupted.

Circuit - An overhead line on poles or underground cables that carry power from substation to the customer. Circuit and distribution lines are used interchangeably. A circuit may also be referred to as a feeder.

Distribution Line - A distribution line is a generic term for a distribution voltage (2,400 volts to 35,000 volts) line that carries power from a substation to a residence or business. These lines may be overhead or underground.

Fault - A fault is an unwanted flow of high current caused by a breakdown of the insulation on a circuit or the introduction of foreign material into a circuit that creates an electrical path to ground. The current flow at the location of a fault may be hundreds of times the magnitude of the normal current flow on a circuit. The introduction of a fault on a circuit will result in the operation of a protective device such as a fuse, recloser or circuit breaker to interrupt that flow of current.

Fuse - An electrical device which interrupts current flow to a circuit when the current exceeds a predetermined value. A fuse is used to protect a specific piece of equipment from damage caused by high currents or can be used to segment off smaller distribution lines from main circuits. Fuses are destroyed when they operate and must be replaced to re-energize a line or piece of equipment after an interruption.

Insulator - An insulator is a piece of equipment made of special material, usually porcelain or a polymer, that supports and separates energized lines and equipment from non-energized parts to prevent unwanted current flows.

Kilowatt - An electrical quantity of energy that equals 1,000 watts.

Megawatt - An electrical quantity of energy that equals 1 million watts.

Meter - A device that plugs into a meter socket that measures the consumption of electricity.

Power Plant - A facility that converts fuel such as gas, oil, coal, nuclear or wind into electrical energy or power.

Recloser - A smaller pole-mounted circuit breaker used on distribution lines.

Secondary Lines - In residential areas, secondary lines will leave the distribution transformer and run for a certain distance. Service lines will then be tapped off of the secondary lines. These are used to serve customers that are not immediately adjacent to a transformer and may be overhead or underground.

Service Line - A service line carries power at voltages 4,160 volts or lower from a distribution transformer to the customers meter. These lines may be overhead or underground.

Substation - A power distribution center where power is stepped down from one voltage to another. It is usually from transmission voltages (69,000 volts to 345,000 volts) to distribution voltages (2,400 volts to 35,000 volts).

Transformer - A device that steps voltage down from a higher voltage to a lower voltage or vice versa. A substation transformer may step voltage down from 138,000 volts to 12,470 volts. A distribution transformer may step voltage down from 7,200 volts to 120/240 for a residence.

Transmission Line - A bare uninsulated high-voltage (69,000 volts to 345,000 volts) overhead line, usually strung from steel towers or tall wood poles, that carries power from power plants to substations.

Watt - The basic unit for measuring energy or power in the utility industry.

© 2019 Oncor Electric Delivery Company LLC.
All Rights Reserved.