LOW VOLTAGE ELECTRICAL TERMS
AC (Alternating current) - An electric current that rises to a maximum in one direction falls back to zero and then rises to a maximum in the opposite direction and then repeats. The electricity in ordinary home or office outlets is AC. Alternating current differs from direct current (DC) in that its direction is reversed 60 times per second (50 times per second in some countries), while DC current flows in one direction only whether pulsed or steady.
Ampere (Amp) - Unit of electrical current.
Amplifier - A circuit that increases the voltage, current, or power of a signal.
Analog - Information represented as continuously varying voltage or current rather than in discrete levels as opposed to digital data varying between two discrete levels.
Battery - A DC voltage source containing two or more cells that convert chemical energy to electrical energy. The most commonly used battery in the security industry is a Sealed-Lead-Acid back-up or stand-by battery.
Circuit - Interconnection of components to provide an electrical path between two or more components.
Circuit Breaker - A protective device used to open a circuit when current exceeds a maximum value - in effect, a reusable fuse.
Closed Circuit - Circuit having a complete path for current flow.
Contact - Current carrying part of a switch, relay or connector.
DC (Direct current) - An electric current flowing in one direction only.
Fuse - A protective device in the current path that melts or breaks when current exceeds a predetermined maximum value.
Ground - An intentional or accidental conducting path between an electrical system or circuit and the earth or some conducting body acting in place of the earth. A ground is often used as the common wiring point or reference in a circuit.
Ohm - Unit of resistance symbolized by the Greek capital letter omega (Ω) � the opposite of Mhos.
Polarity - Term used to describe positive and negative charges.
Power Supply - Electrical equipment used to deliver either AC or DC voltage - can be Linear or Switching.
Linear - A linear regulated supply maintains a constant output voltage by throwing away the difference between input and output voltage times current as heat. Linear power supplies are classified as such because they eliminate excess energy (power) by dissipating heat to the surrounding air. This form of conversion is simple and thus was the first to be used for power supplies. Simplicity also constitutes the major advantage of linear power supplies. The major disadvantage to them is their lack of efficiency, usually only 30-50%.
Relay - An electromechanical device that opens or closes contacts when a current is passed through a coil.
Voltage (V) - Term used to designate electrical pressure or force that causes current to flow.
Volt - Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one ohm.
Volt-Ampere (VA) - Unit of apparent power in an AC circuit containing capacitive or inductive reactance. Apparent power is the product of source voltage and current.
Watt - Unit of electrical power required to do work at the rate of one joule per second. One watt of power is expended when one ampere of direct current flows through a resistance of one ohm. In an AC circuit, true power is the product of effective volts and effective amperes, multiplied by the power factor.