Metric Prefixes:
Electrical terms are often used with a prefix to indicate larger or smaller values. The following table indicates those most frequently used in the electrical industry.

MILLI = 1/1000th = 1 Milliamp = 1/1000th of an AMP
KILO = 1,000 = 1 Kilowatt = 1,000 watts and/or 1 kilovolt = 1,000 volts
MEGA = 1,000,000 = 1 Megawatt = 1,000,000 watts


Electrical Terms:

  • Ampere (amp) – An International System unit of electrical current flow
  • Circuit Breaker – An electrical switching device that automatically opens when the current in the circuit exceeds the design limits of the breaker. Its purpose is to protect the circuit from damage due to excessive current. Circuit breakers are normally rated in amps.
  • Conductor – A material that allows electricity to flow through it easily. Water and most metals are good conductors. Conductors can allow electricity to flow through them because the electrons in their atoms move slowly.
  • Demand – Refers to the demand for electricity measured as the rate of energy consumption. Instantaneous demand is measured in Kilowatts and demand over a period of time is measured in kilowatt hours.
  • Energy use – The total amount of energy consumed over a specific period of time. When discussing electrical energy use, it is measured in kilowatt hours (kwh).
  • Generator – A machine converts mechanical energy into electrical energy.
  • Ground – A non-current carrying wire connected to earth. The ground wire (usually the green wire) provides some degree of protection to the person operating an electrical device in the event of a short circuit.
  • Hertz – Frequency of AC voltage oscillations in cycles per second. The United States electrical system operates at 60HZ.
  • Insulator – A material that resists the flow of electricity because the electrons do not move easily from atom to atom. Glass and some plastics are examples of good insulators.
  • Kilowatt – A unit of electrical power demand equal to 1,000 watts of electricity.
  • Kilowatt-hour – A measure of electrical power consumed over time. One kilowatt of electricity consumed in one hour.
  • Megawatt – 1,000,000 watts of power or 1,000 kilowatts
  • NEMA – The National Electrical Manufacturers Association, which sets the standards for electrical equipment used in the United States.
  • Neutral – A conductor that is common to other circuits and carries no current. Usually the neutral measures 0 volts.
  • Peak Demand – The maximum amount of electrical energy consumed in any one 15 minute period during the customer’s billing cycle. Customers typically pay a premium for their highest peak demand during the billing cycle.
  • Polarity – A measure of whether an electrical terminal contains a positive voltage or negative voltage.
  • Power Factor – In an ideal AC electrical system, the voltage and current are in sync with each other. In other words, current flow increases as voltage increases and current flow decreases on the sine wave. However, certain types of devices such as transformers, magnetic ballasts (HIDs), electric motors, and so on, can cause current and voltage to go out of sync with each other. This reduces the efficiency of the electrical devices and causes the utility to have to generate more power to compensate for the inefficiency. 1.0 is considered to be a perfect power factor.
  • Step down transformer – A transformer that produces an output voltage that is lower than the input voltage.
  • Step up transformer – A transformer that produces an output voltage that is higher than the input voltage.
  • Substation – A facility where transformers lower electricity’s voltage from the transmission system voltage.
  • Transformer – A device used to increase or decrease electricity’s voltage.
  • Voltage – A measure of the electrical pressure in an electrical system.
  • Wattage – A measure of the amount of electrical work done or power consumed.