Alarm System Terminology
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Access Control: The means of influencing and regulating the flow of persons through a door
(entry and/or exit).
Actuator: The mechanism of the switch or switch enclosure that operate the contacts.
Adjustable: The ability to change or ALTer the time delay or other parameter by means of an adjustment,
such as a potentiometer, a resistor, or a switch.
Alarm: A device used to indicate an emergency or other specific condition.
ALTernating Current (AC): An electric current that reverses its direction regularly and continually. The
voltage ALTernates its polarity and direction of current flow negative to positive. AC current increases to a peak,
decreases through zero, and peaks in the opposite direction. AC current flows back and forth in the conductor and
is expressed in cycles per second, or Hertz (Hz).
Ambient Temperature: The temperature of the air immediately surrounding a device or object.
Alligator Clip: A mechanical device, shaped like the jaws of an alligator, used as a temporary connection on the
end of a test lead or jumper wire.
American National Standards Institute (ANSI): A federation of trade, technical, and professional
organizations, government agencies.
Ampere (amp): The unit of measurement for the rate of electrical current flow, characterized by the
symbols I (in Ohm's law formulas) or A. One ampere is the current flowing through one ohm of resistance at one
Ampere/Hour (AH): A measurement of a battery's capacity. One ampere of current flowing for one hour
equals one ampere/hour.
Annunciator: An audible and, or visual signaling device.
Arc: An electrical current through air or across the surface of an insulator associated with high, voltage.
An arc usually occurs when a contact is opened, deenergizirg an inductive load. Arcing of a contact will limit its
Armor: A metal jacket surrounding wires for mechanical protection.
Authorized Release Device: A device that, when activated, allows authorized persons to enter or exit monitored
and controlled openings without triggering an alarm. The authorized passage release may be a keyed switch,
a card reader, a digital code reader, and so forth.
Battery Standby: A means of automatically switching over to stored battery power during local primary
Bell Wire: 18 gauge insulator solid copper wire, used for making doorbell and thermostat connections in
Block Diagram: A drawing that shows the relationship of equipment in a system. Blocks used to represent each
piece of equipment are arranged into a system diagram that shows their physical or operational relation to
Bolt: The projectable member of a lock or latch mechanism that engages the door frame and the strike.
(See deadbolt and latchbolt.)
Bolt Position Switch: A miniature switch used on or in a locking device to monitor whether the locking bolt is
in the locked (projected) or unlocked (retracted) position.
Box Strike: A strike in which the latchbolt recess is enclosed or boxed, thus covering the opening in the
Break: To open an electrical circuit.
Breakdown voltage: The voltage at which the insulation between two conductors is destroyed.
Brownout: Low line voltage, which can cause mis-operation of and possible damage to equipment. For example,
a motor that tries to start at low voltage can actually be in a lock-rotor condition and can overheat.
Bus: A common return path in electric circuits.
Cable: A group of insulated conductors in a common jacket.
Cable Clamp: A device used to give mechanical support to a wire bundle or cable.
Cable Tie: A belt-like plastic strip that loops around bundles of cables or insulated wires to hold them
Cam: A rotating eccentric piece attached to the end of a cylinder plug to actuate a lock or latch
Case: A housing for a lock mechanism.
Chip: A micro-miniature electronic circuit on a tiny silicon wafer or other conductive material.
Circuit: The path through which electrical energy flows.
Circuit, Closed: (1) An electrical circuit in which current normally flows until interrupted by the opening of
a switch or a switch-type electronic component. (2) A circuit or switch in which the contacts are closed during
Circuit, Open: (1) An electrical circuit in which current does not flow until permitted by the closing of a
switch or a switch-type electronic component. (2) A circuit or switch in which the contacts are open during
Closure: The point at which two contacts meet to complete a circuit.
Coaxial Cable: A cable consisting of two cylindrical conductors with a common axis. The two conductors are
separated by a dielectric. The outer conductor, normally at ground potential, acts as a return path for current
flowing through the center conductor and prevents energy radiation from the cable. The outer conductor,
or shield, is also commonly used to prevent external radiation from affecting the current flowing in the inner
conductor. The outer shield or conductor consists of woven strands of wire or is a metal sheath.
Code Bypass: A means of opening a door from inside the protected area (usually by pressing a button)
without entering a key or code in the key reader.
Coded Card: A plastic card (usually polyvinyl chloride) that has a combination (three to six digits, secreted
in its design either in a series of small magnets or on magnetic tape (mag stripe).
Coil, Electric: Successive turns of insulated wire that create a magnetic field when an electric current is
passed through them.
Cold Solder Joint: A solder connection that exhibits poor wetting and a grayish, porous appearance due to
insufficient heat, inadequate cleaning prior to soldering, or excessive impurities in the solder solution.
Conductance: The ability of an electrical conductor to pass current; the reciprocal of resistance.
Conductivity: The capability of a material to carry electrical current-usually expressed as a percentage of
copper conductivity (copper being 100 percent).
Conductor: Material with the ability to carry electric current. The term is also used for an electric wire.
Conduit: A tube or trough for protecting electrical wires or cables. It may be a solid or flexible tube in
which insulated electrical wires are run.
Connector: Generally, any device used to provide rapid connect/disconnect service for electrical cable and
Contact Chatter (Contact Bounce): A condition that sometimes occurs on closure of two contacts. when a
mechanical contact closes, the contacts make and break several times before a stable closed condition is
established. Bounce or chatter can also be caused by external vibration or shock on a closed contact.
Contacts: Electrically conductive points, or sets of points, used to make or break an electrical circuit
Continuity: The state of belief, complete and uninterrupted, like a normally closed circuit.
Continuity Check: A test performed on a length of wire or cable to determine whether the electrical current
flows continuously throughout the length.
Continuous Duty: Refers to a device or a control that can operate continuously with no off or rest
Continuous Duty Locking Unit: An electric lock equipped with a heavy-duty solenoid that can be energized
Control Box: A sheet metal enclosure that contains electronic and electromechanical controls and circuitry.
Crimp: To compress (deform) a connector barrel around a cable in order to make an electrical connection.
Crimp Termination: A connection in which a metal sleeve is secured to a conductor by mechanically crimping
the sleeve with pliers, presses, or automated crimping machines. Splices, terminals, and multi-contact connectors
are typical terminating devices attached by crimping. Crimping is suitable for all wire types.
Current: The flow of electrons through an electrical conductor. Current is measured in amperes.
Current-Carrying Capacity: The maximum current an insulated conductor can safely carry without exceeding
its insulation and jacket temperature limitations.
Cycle (Frequency): The number of times per second the current in an ALTernating current system reverses
its direction of flow. The standard commercial current in the United States is 60-cycle (6OHz).
Cylinder: A housing that contains a tumbler mechanism and a key-way plug that can be turned only by the
correct key. It includes a cam or spindle to transmit rotary action to a lock or latch mechanism. For security and
keying versatility, authorities generally specify a pin-tumbler cylinder of no fewer than five pins. The two types
of cylinders, the mortise cylinder (round, threaded housing) and the bored lock cylinder (sometimes called a
cylinder insert), which both provide the same functional value of security and convenience and are often included
in the same keying system. (See Keying.)
Deadbolt: A bolt operated manually and not actuated by springs. When locked, the bolt cannot be forced
back. A deadbolt is operated (projected and retracted) by a key cylinder or lever handle.
Deadlatch: A latch in which the latchbolt is positively held in the projected position by an auxiliary
Decibel (dB): An increment of measurement used to compare measured levels of sound energy (intensity) to the
apparent level detected by the human ear, expressed as a logarithmic ratio. A sound that has 10 times the energy
of another sound is said to be 10 decibels louder; 100 times the energy is 20 decibels louder; 1,000 times the
energy is 30 decibels louder; and so on. Decibel levels are correctly expressed as the number of decibels at a
measured distance from the course of sound (for example, 125 dB at 10 feet).
Deenergize: To remove power.
Delay: A period of time before or during an event.
Delay on Break: A term used to describe a mode of operation relative to timing devices. The delay begins
when the initiate switch is opened (delay on break of initiate switch).
Delay on Energization: A term used to describe a mode of operation relative to timing devices. The delay
begins when the initiate switch is closed or on application of power to the input.
Delay: on Make Same as delay on energization.
Dielectric: Any insulating material between two conductors that permits electrostatic attraction and repulsion
to take place across it.
Digital Printer: A device that receives electronically coded signals and prints this information on a
DIP Switch: A miniature switch used to program, set, or change circuit functions. DIP is an abbreviation for
the dual-in-line package, which houses the switch.
Direct Current (DC): Electrical current that travels in only one direction and has negative (-) and
positive (+) polarity. It may or may not have an AC ripple component. DC sources that are unfiltered should be
referred to as full-wave or half-wave rectified AC.
Door Status Switch: A DSS is a switch used to monitor whether a door is in an opened or closed position.
Double Pole, Double Throw (DPDT): A term used to describe a switch or relay output contact form
(2 form C) in which two separate switches are operating simultaneously, each with a normally open and normally
closed contact and a common connection. This form is used to make and break two separate circuits.
Dry Contact: Metallic points making (shorting) or breaking (opening) a circuit. The switched circuit must
have its own source of power and is merely routed through the dry contacts.
Duty Cycle: The percentage of on time or operating time of a device. For example, a device that is on for one
minute and off for nine minutes is operating at a 10 Percent duty cycle.
Electric Door Strike: An electric door locking device (usually solenoid-operated) that will unlock the door
when electrical power is applied to it. A fail-safe configuration will operate in the reverse condition
(i.e., normally locked when power is applied and unlocked when power is interrupted).
Electromagnet: A coil of wire, usually wound on an iron core, that produces a strong magnetic field when
current is sent through the coil.
Electromagnetic: Pertaining to combined electric and magnetic fields associated with movements of
electrons through conductors.
Electromotive Force (EMF): Pressure or voltage; the force that causes current to flow in a circuit.
Emergency Release: An optional feature of a lock that provides a means of overriding the lock and
retracting the bolt in an emergency. It can be operated either mechanicallv or electrically.
Encapsulant: A material, usually epoxy, used to encase and seal all components in an electronic circuit.
End-of-Line (EOL)Resistor: Resistance in a supervised circuit, usually at the farthest point from the alarm
control unit, restricting the flow of current to a known value, which is monitored. Shorting the circuit in an
attempt to bypass protective devices in the loop (e.g., door contacts) will create increased flow of current and
cause an alarm. Opening (breaking) the circuit also triggers an alarm if the system is armed or a supervisory
signal if the system is disarmed.
Energize: To apply power.
Explosion-Proof Device: Any device, such as a contact switch, that is enclosed in an explosion-proof housing
to help prevent possible sparking in potentially volatile environments.
External Adjustment: A device, outside the control, that is used to ALTer or change the controlled parameter
(e.g., an external potentiometer with a time-delay control).
Factory Calibration: Tuning or ALTering of a control circuit by the manufacturer to bring the circuit into
specification; normally stated as a percentage deviation.
Factory Fixed: Refers to adjustment made by the manufacturer and not accessible to the user.
Fail-Safe Lock: An electric lock that automatically unlocks with any power interruption.
Fail-Secure Lock: An electric lock that requires power to unlock.
Fast-on Terminal: A solderless, easy-to-use, female/male push-on terminal that comes in various sizes.
It is a common termination for controls and is widely used in automotive, appliance, and other OEM equipment.
Fire Door Latch: A latch that has a 3/4-inch throw and an anti-friction retractor.
Flasher: A control in which the, out put to the load (normally a lamp) is turned on and off repeatedly at a
given rate of operation or flashes per minute (FPM).
Flux: (1) The lines of force that make up an electrostatic field. (2) The rate of flow of energy across or
through a surface. (3) A substance used to promote or facilitate fusion, such as a material that removes
oxides from surfaces to be joined by soldering or welding.
Form C Contact: A switch mechanism that contains three terminals (normally open, common, and,
Frequency: The number of complete operations or cycles that take place within a given period of time
(normally one second), as in the AC line frequency of 6OHz (61) cycles per second).
Full-Wave: A term used for both AC and DC voltages, suggesting that both halves of the same wave are utilized
(e.g., full-wave AC and full-wave rectified AC, or unfiltered full-wave DC).
Fuse: A protective device, placed in a circuit as a safeguard, that contains a strip of easily melted
metal. When the current flow becomes too great, the metal melts, thus breaking the circuit.
Gold: A very soft, ductile material that is noted for its resistance to corrosive media. It is used
primarily as a coating or plating.
Ground: A conducting connection between an electrical circuit and the earth or other large conducting body
to serve as an electrical ground, thus making a complete electrical circuit.
Ground, Earth: The portion (if a circuit that is connected to a buried metallic object such as a grounding
rod or water pipe.
Half-Wave: Refers to the passing or the use of only one-half of the AC sine wave. The result is half-wale
rectified AC, or unfiltered half-wave DC.
Hand of Door: The description of swinging door operation, always viewed from outside the room, building,
and so forth. Left hand means that the door hinges on the left and right hand means that the door hinges on
Hard-Wired: Refers to groups of connections that require the use of wire conductors.
Heat Sink: A method used to transfer a rise in temperature by means of a metal plate or fin-shaped object
with good heat transfer efficiency that helps dissipate heat into the surrounding air, into a liquid, or into
a larger mass.
Heat Sink Compound: A silicon compound filled with alumina or some other heat-conductive oxide. It is used to
fill voids and irregularities in surfaces between two mating objects to permit optimum heat transfer.
Hertz (Hz): The international unit of frequency equal to one cycle per second; named after the German
physicist Heinrich Rudolph Hertz (1857-94).
Hi-Pot: A test designed to determine the highest potential that can be applied to a conductor without
breaking through the insulation.
Hookup Wire: Insulated wire used for low-current, low-voltage (under 1,OOOV) applications internally
within enclosed electronic equipment.
Humidity: The amount of moisture in the air, measured in percent of relative humidity.
Impedance: The opposition in an electrical circuit to the flow of an ALTernating current (AC). Impedance
consists of ohmic resistance (R), inductive reactance (XI), and capacitive reactance (Xc).
Incandescent Lamp: An electric lighting and signaling device that operates on the principle of heating a fine
metal wire filament to a white heat by passing an electrical current through it. The filament wire has a
positive temperature coefficient that results in high inrush currents, up to ten times the steady state current. apparent communication; electrifying, magnetizing, or inducing voltage by exposure to a field.
Induction: An influence exerted by a charged body or by a magnetic field on neighboring bodies without
apparent communication; electrifying, magnetizing, or inducing voltage by exposure to a field.
Inductive Load: An electric device made of wire, wound or coiled, to create a magnetic field to produce
mechanical work when energized. Components such as motors, solenoids, and relay coils are all inductive loads
by nature. An inductive load can exhibit an inrush or lock-rotor current of up to five times its normal running or
steady state current when energized. When de-energized, the magnetic field collapses and a high-voltage
transient is generated, which can cause arcing across contacts or a malfunction of and/or damage to electronic
circuits. When transients are present, they should be suppressed. (See Transient.)
Input Voltage: The designed power source requirement needed by equipment in order to operate
Inrush: The initial surge of current through a load when power is first applied. Lamp loads, inductive motors,
solenoids, and capacitive load types all have inrush or surge currents higher than the normal running or
steady state currents. Resistive loads, such as heater elements, have no inrush.
Insulation: A material that provides high electric resistance, making it suitable for covering components,
terminals, and wires to prevent possible future contact of adjacent conductors, resulting in a short circuit.
Interlock: A system of multiple doors with controlled interaction. Interlocks are also known as lightraps,
airtraps, mantraps, and sallyports. (See Safety Interlock, Security Interlock.)
Intermittent Duty Solenoid: A solenoid designed to be energized for short periods of time. Continuous
operation may damage an intermittent duty solenoid.
Interval: A period of time from one event to another. An interval timer controls the time for which a load
is energized or de-energized.
Isolation: No electrical connection between two or more circuits.
Jacket: Pertaining to wire and cable, the outer sheath that protects it against the environment and also
provide additional insulation.
Jumper: A short length of conductor used to make a connection between terminals, around a break in a
circuit, or around an instrument. It is usually a temporary connection.
Junction: A point in a circuit where two or more wires are connected.
Junction Box: A protective enclosure for connecting circuit wires.
Keying: The various keying arrangements for pin-tumbler cylinders: individual key-the key for an individual
cylinder; keyed alike-all cylinders may be operated by the same key (not to be confused with master keyed); keyed
different-a different individual key operates each cylinder (or group of cylinders); master key-a key to operate a
group of cylinders, each of which may be set to a different individual key; master keyed-all cylinders in a group
can be operated by one master key, ALThough all cylinders may be keyed differently
(not to be confused with keyed alike).
Kilohm One: Thousand (10') ohms.
Labeled: Refers to equipment or materials that have a label, symbol, or other identifying mark of ar,
organization that is approved by the authority having jurisdiction over product evaluation. The label
indicates compliance by the manufacturer with appropriate equipment or performance standards.
Latch: The locking in of a circuit by means of a holding contact; used in relay logic when a momentary
initiation is required.
Latchbolt: A device for automatically retaining a door in the closed position upon its closing; a beveled
spring-loaded bolt that automatically seats in the strike on contact. Retracted by key cylinder or lever handle.
Life: The number of performance hours, davs, years, or actual operations for which an item is designed.
Light-Emitting Diode (LED): A diode, a solid-state device, that gives off virtually heatless colored light when
electric current is passed through it. LEDs are very efficient and long-lasting and are often used for digital
readouts and annunciators. Common colors include red, green, and amber.
Lighttrap or Airtrap: A room with two or more doors controlled to prevent more than one door being
opened at one time.
Line Cord: A cord, terminating in a plug at one end, that is used to connect equipment or appliances to a
Line Drop: A voltage loss occurring between any two points in a power or transmission line. Such loss, or
drop, is due to the resistance, reactance, or leakage of the line.
Line Supervision: The electrical supervision of a wire run to detect tampering (a cut or shorted wire).
Line supervision usually requires a terminating element at the end of the monitored wire loop.
(See End of-Line Resistor.)
Line Voltage: The voltage existing in a main cable or circuit, such as at a wall outlet.
Listed: Refers to equipment or materials included in a list published by an authorizing organization.
The listing states that the equipment or material meets appropriate standards or has been tested for and is suited
to a specific application.
Load: Any device that consumes electrical power; the amount of power required for operation of a circuit
Load Rating: A control specification outlining the type of load, the minimum (min.) and the maximum (max.)
currents, and the voltage. local alarm A visual or audible signaling device located at a monitored door, window,
or other opening.
Lock: A device for securing a door in the closed position against unauthorized or forced entry. It requires
actuation to project or to retract its bolt.
Maintained Contact Switch: A switch designed for applications requiring sustained contact, but with
provision for resetting.
Make: To Close or establish an electrical circuit.
Mantrap: See Interlock.
Maximum Rating: The absolute maximum condition in which a device is designed to operate. Voltage,
frequency, current, temperature, humidity, shock, and other parameters can be specified as maximum.
Megohm: One million (10’) ohms.
Mil: One one-thousandth (0.001) of an inch; a unit used in measuring the diameter of wire and the
thickness of insulation over a conductor.
Milliampere: One one-thousandth (0.001) of an ampere.
Millisecond: One one-thousandth (0.001) of a second.
Mode of Operation: The specified operational condition of a switch, lock, door system, and so forth.
Momentary Duty Lock: An electric lock equipped with a solenoid that is energized only momentarily.
Momentary Loss of Power: A short interruption of power to the total equipment.
Momentary Switch: A spring-loaded contact that, when pressed, closes two contacts. When pressure is
removed, the contacts open.
Monitoring Loop: A continuous loop of wire starting at the control panel and running through switches in
a system to indicate a breach of security through an open switch or a cut wire.
Mother Board: A master printed circuit board used to interface the activities of individual printed circuit
boards and the devices being controlled or monitored. The mother board is usually located at the back of a control
panel assembly; individual printed circuit boards plug into it.
Multiconductor Cable: A cable consisting of two or more conductors, either cabled or laid in a flat parallel
construction, with or without a common overall covering.
Multiplex: Refers to a system of transmitting several messages simultaneously on the same circuit or
channel. Multiplex equipment greatly reduces the number of wire cables needed in a system.
National Electrical Code (NEC): A consensus standard published by the National Fire Protection Association
(NFPA); commonly called "code."
Noise: Unwanted and/or unintelligible signals picked up on a cable circuit.
Normally closed (NC): The condition or position of a contact prior to initiation or energization-in this case,
a closed condition.
Normally Open (NO): The condition or position of a contact prior to initiation or energization-in this case,
an open condition.
Occupancy Indicator: A visual indication to service personnel that a room is occupied; consists of a small
pin in the outside cylinder that is extended by pressing the inside button.
Octal Plug: An eight-pin male connector with a locating key for proper orientation.
Ohm: A unit of measurement for resistance (R) and impedance (Z).
Ohm's Law: One of the most widely used principles of electricity. It expresses the relationship between
voltage (E), current (I) and resistance (R) according to the following equations: E = IR; I = E/R; R = E/I.
Operating Temperature: A temperature range over which a device will perform within its specified design
tolerances; may be stated in degrees Fahrenheit ('F) or degrees centigrade (C).
Operating Voltage: The voltage by which a system operates; a nominal voltage with a specified tolerance
applied; the design voltage range necessary to remain within the operating tolerances. For example, for a system
specified 120 volts +/- 10 percent of nominal, 120 volts is the nominal voltage and the design voltage range is
108 to 132 volts AC.
Output Voltage: The designed power source produced by a power supply to operate equipment.
Panic-Proof Locks: Locks that provide immediate exit from the inside at all times.
Parallel: A method of connecting an electric circuit whereby each element is connected across the other.
The addition of all currents through each element equals the total current of the circuit.
Passbox: A wall opening between rooms through which material is transferred.
Polarity: The positive or negative orientation of a signal or power source.
Potentiometer (pot): Variable resistor.
Primary : he transformer winding that receives the energy from a supply circuit.
Printed Circuit Board: A means of making electrical interconnections without using insulated wires. Printed
circuit boards provide a supporting and insulating medium for components and conductors in a form that is
readily adaptable to machine assembly.
Rack-Mounted: Refers to a method of housing many control and security panels. Nineteen-inch rack
mounting is a standard for the electrical equipment trades. Rack mounting allows equipment of several different
manufacturers, different types of communications, fire/ smoke alarm, and security equipment to be used in the
same area without taking up a large amount of space. It also achieves a more uniform and organized appearance.
Rated Voltage: The maximum voltage at which an electric component can operate for extended period,
without undue degradation or safety hazard.
Reactance: Opposition offered to the flow of ALTernating current by inductance or capacitance of a
component or circuit.
Rectifier: A solid state electrical device that will allow current to flow in one direction only. It is designed
to convert ALTernating current to direct current.
Recycle Time: The time needed if reset and reinitiate the timing function and remain within the specified
timing tolerances. Recycle time is generally specified "during timing" or "after timing."
Regulated Power Supply: A power supply that provides a constant output regardless of input voltage.
Relay: An electrically controlled device that opens and closes electrical contacts to effect the operation of
other devices in the same or another electrical circuit.
Remote Alarm: A visual or audible signaling device used to signal violations at locations removed from the
central control station or monitored openings. For example, a remote alarm may be placed on a roof, in a
stair tower, or at guard stations outside a building.
Remote Reset: A switch located at a monitored opening. If a violation occurs, the alarm at the main control
console cannot be turned off until the door is secured and the remote reset is activated. Its purpose is to
ensure the inspection of an opening that has been violated or left open.
Reset Time: The time required to return the output to its original condition.
Resistance: The opposition to the flow of an electric current (measured in ohms); the reciprocal of
Resistor: A circuit element whose chief purpose is to oppose the flow of current.
Resolution: The degree of set-ability.
Reverse Polarity Protected: Applies to DC controls where, if the polarity of the input were reversed,
there would be no damage.
Rigid Conduit: A metal piping for housing the insulated wires of an electric circuit.
Riser Diagram: A document which explains wire type, size, and the number of conductors to be run from a
control panel to each control or monitor location.
Root-Mean-Square (RMS): A term applied to ALTernating voltage and current that means the effective
value; that is, it produces the same heating effect as a direct current or voltage of the same magnitude. It
is also a means of expressing AC voltage in terms of DC (usually approximately 80 percent of the AC peak
Safety Interlock: A multi-door system in which all doors are normally closed and unlocked; opening any door
locks all other doors.
Sallyport: See Interlock.
Secondary: The transformer winding that receives energy by electromagnetic induction from the primary.
Security Interlock: A multi-door system in which all doors are normally closed and locked; releasing one
door disables the releases for all other doors until the first door is closed and locked again.
Semiconductor: A material that has a resistance between that of insulators and conductors.
Series Circuit: An electrical circuit in which all the receptive devices are arranged in succession, as
distinguished from a parallel circuit. The same current flows through each part of the circuit in sequence.
Shield: In cables, a metallic layer placed around a conductor or group of conductors to prevent electrostatic
interference between the enclosed wires and external fields.
Short: An improper connection between "hot" current-carrying wire and neutral or ground.
Silver: A metal, similar to gold in corrosion resistance, that costs less than other precious metals. It is very
soft when fully annealed but work-hardens during fabrication. It provides very good conductivity and
solderability. It is widely used as a plating or coating.
Single Pole, Double Throw (SPDT): A term used to describe a switch or relay contact form (1 form C) that
has a normally open and a normally closed contact with a common connection.
Single Pole, Single Throw (SPST): A switch with only one moving and one stationary contact, available either
normally open (NO) or normally closed (NC).
Solenoid: An electromechanical device that operates the lock-bolt. When electricity is applied, a mechanical
motion is obtained that moves the bolt.
Soldering: A method of making an electrical connection. The two components to be connected are physically
placed together and heated. Solder, a conductive metallic alloy with a low melting point, is then placed on the
heated components. It melts and flows around the components to make a permanent connection.
Spike: A momentary increase in electrical current. Spikes can damage electronic equipment.
Splice: A connection of two or more conductors or cables to provide good mechanical strength as well as
Springlatch: A plain latch with a beveled latch-bolt that is activated by springs.
Standard Duty Locking Unit: An electric lock equipped with a solenoid that is energized for short periods of
time, not continuously.
Steady State: A term used to specify the current through a load or electric circuit after the inrush current
is complete; a stable run condition.
Storage Temperature: The maximum temperature that any one material in a system can withstand
without sustaining damage; a non-working condition.
Stranded Conductor: A conductor composed of several single solid wires twisted together.
Strike: A plate mortised into or mounted on the door jamb to accept and restrain a bolt when the door
is closed. In some metal installations of a deadlock, the strike may simply be an opening cut into the jamb.
Supervised Circuit: A circuit that will indicate alarm and trouble conditions.
Switches: Devices that make or break connections in an electrical or electronic circuit. In computing systems,
they are also used to make selections (the toggle switch, for example, completes a conditional jump). Switches
are usually manually operated but can also work by mechanical, thermal, electromechanical, barometric,
hydraulic, or gravitational means.
Switch, Momentary: A switch that, when activated, automatically returns to its original position afterwards.
Switch, Maintained: A switch that, when activated, maintains its activated position until it is not
Switch, Normally Open: A switch that, when not energized, is open and does not permit current to flow.
Switch, Normally Closed: A switch that, when not energized, is closed to form a path for current.
Tap: A special lead brought out from an intermediate point of a coil or winding.
Telephone Wire: A very general term referring to many different types of communication wire. It refers to a
class of wires and cables, rather than a specific type.
Terminal Block: A device that provides a place for safe and convenient interconnection of current-carrying
Terminals: Metal wire termination devices designed to handle one or more conductors and to be attached
to a board, bus, or block with mechanical fasteners or clipped on. Common types are ring tongue, spade, flag,
hook, blade, quick-connect, offset, flanged. Special types include taper pin, taper tab, and others, insulated
and not insulated.
Terminating Element: An electric device connected at the end of a pair of electrical conductors that provides
the means of supervising those conductors. (See Line Supervision.)
Time Delay: An electronically controlled delay period designed into a component that will either send a
prolonged signal or delay transmitting a signal.
Time-Delay Relay: A relay for automatically locking or unlocking a locking unit after a short, fixed time
Tinned Copper: Copper with a tin coating added to aid in soldering and to inhibit corrosion.
Tolerance: Normally stated as a percentage, the maximum allowable deviation of electrical, environmental,
or dimensional parameters.
Transformer: An electric device that changes voltage in direct proportion to currents and in inverse
proportion to the ratio of the number of turns of its primary and secondary windings. The input side of a
transformer is called the primary side; the output or low-voltage side is called the transformer secondary.
Transient: Any increase or decrease in the excursion of voltage, current, power, heat, and so forth, above
or below a nominal value that is not normal to the source. (See Transient Voltage.)
Transient Voltage: Refers to several parameters of a transient: (1) the peak or maximum voltage reached,
(2) the rate of rise of the transient (dv/dt), and (3) the duration of the transient. Transient voltages are
generated when inductive load, such as solenoids, contactors, motors, relays, and so forth, are de-energized.
ALThough some devices have excellent protection against tecse sometimes damaging excursions, when a transient
is known to be present, it should be suppressed at the source. Diodes and metal oxide varistors (MOVS) are
commonly used as suppressors.
Trickle Charge: A low-powered electrical energy source provided to keep standby batteries fully charged.
Twisted Pair: A cable composed of two small insulated conductors, twisted together without a common
covering. The two conductors of a twisted pair are usually substantially insulated, so the combination is a special
case of a cord.
Volt (V): A unit of electromotive force. It is the difference of potential required to make a current of one
ampere flow through a resistance of one ohm.
Voltage: The term most often used (in place of electromotive force, potential, potential difference, or voltage
drop) to designate electrical pressure that exists between two points and is capable of producing a flow of
current when a closed circuit is connected between the two points.
Voltage Drop: Voltage loss experienced by electrical circuits due to two principal factors: (1) wire size and (2) length of wire runs.
Volt/amp (VA)rating: The product of rated input voltage multiplied by the rated current. This establishes the
"apparent energy" available to accomplish work.
Watt: The common unit of electrical power. One watt is dissipated by a resistance of one ohm through
which one ampere flows.
Wire: A slender rod or filament of drawn metal.
Wire Nut: A connector used to make and insulate an electrical connection. Wire ends are stripped and placed
into a cap-like connector (wire nut), and the wire-nut is then twisted to secure the wire ends together. The
cap design serves to insulate the connection.
Zone: A specific area of protection; a portion of a large protected area.