Electricity for Refrigeration, Heating and Air Conditioning: Glossary

- A -

air-cooled packaged unit: A unit that's made in one complete unit with an air-cooled condenser mounted with the unit or remotely.

alternating current: Electron flow that flows in one direction and then reverses at regular intervals; produced by cutting a magnetic field with a conductor. The most common type of power supply used in the heating, cooling, and refrigeration industry.

alternator: An electrical generator that's used to produce alternating current.

ambient air temperature: The temperature of the air surrounding any device.

American Wire Gauge: Standard unit of measurement for wire.

ammeter: An electric meter used to measure the amperes that are present in a circuit. Ammeters are made as in-line ammeters or clamp-on meters.

ampere: The amount of current required to flow through a resistance of one ohm with a pressure of one volt, measured with an ammeter

analog meter: A device that uses a meter movement to indicate an electrical characteristic.

anti-short-cycling device: A device that pre vents a load from stopping and starting in rapid succession. This device is used mainly to prevent compressors from stopping and starting rapidly.

anticipator: A component of a thermostat that anticipates the temperature of an area and will stop or start the cooling or heating equipment to prevent the thermostat from overshooting the desired temperature

apparent wattage: The power that's calculated by multiplying the voltage times the amperage of a circuit.

armature: The portion of a contactor that moves; connected to a set of contacts that causes a completed circuit when the armature is pulled into the magnetic field produced by the coil.

atom: The smallest particle of an element that can exist and maintain any identification; can combine with other atoms to form new substances

- B -

back electromotive force: The amount of volt age produced across the starting and common terminals or connections of a single-phase motor.

balance point: The point at which the capacity of a heat pump equals the heating load of the structure. At this point additional heat will be needed to meet the load of the building.

ball bearing: An antifriction device that's used to allow free turning and support of the rotating member of the device. It consists of an outer ring and inner ring with races and has steel balls sandwiched between the rings.

bearing: The part of a rotating machine or motor that allows free turning of its rotating parts with little friction.

bimetal overload: A simple thermal overload that breaks the power supplying a small motor directly. When it reaches a high enough temperature, the bimetal opens by warping; when the over load cools, the bimetal will warp back and close the circuit.

bimetal relay: An overload device that opens a set of contacts by a temperature that corresponds to the current draw of a load.

breaker: A device usually used in a breaker panel that's capable of being used as a disconnect switch and an overload protection for the circuit it's sup plying power to.

breaker panel: An electric panel that houses breakers used to distribute power to circuits in the structure.

- C -

cad cell: A light-sensitive cell that changes its resistance in the presence of light. In most cases, the resistance decreases as the cell views the light. The cad cell is used to detect the ignition of an oil burner.

callback: A return trip to a piece of equipment that was not properly serviced the first trip.

capacitive reactance: A resistance caused by using capacitors with motors; when a capacitor is put in a circuit, it resists the voltage change, causing the amperage to lead the voltage.

capacitor: A device that consists of two aluminum plates with an insulator between the plates; used to boost the starting torque of single-phase motors. The two types of capacitors are electrolytic or starting, and running or oil filled.

capacitor-start-capacitor-run motor: A high starting torque and good running efficiency motor; it uses a starting capacitor to increase starting torque and a running capacitor to increase running efficiency.

capacitor-start motor: A motor that uses a starting capacitor to increase the starting torque.

capacity control: The action of limiting the capacity of a piece of equipment to meet the needs of the load. Capacity control is used in light commercial and larger commercial and industrial applications.

cardiopulmonary resuscitation (CPR): The action taken by others after a cardiac arrest has occurred in which breathing and massage of the heart are attempted for the victim.

charge: A condition in which an imbalance of protons and electrons exists in an atom.

circuit breaker: See breaker.

circuit lockout: A method used to lock out a circuit that a technician is working on to prevent some one from restoring electrical energy to the circuit.

clamp-on ammeter: A type of ammeter with jaws that clamp around one of the conductors sup plying power to the load.

clock thermostat: A thermostat that's used to control the temperature of a structure with a time function that can be set or programmed by the occupant of the structure. Clock thermostats can have multiple programs adding to their flexibility.

closed circuit: A complete path for electrons to follow.

coil: An electrical device that's used to convert electrical energy into a magnetic field.

combustion chamber: The part of a fossil fuel appliance where the combustion occurs.

compound: A substance that's a combination of atoms from at least two different elements.

compressor: A device that's used in a mechanical refrigeration system to compress the refrigerant. Most compressors are rotated by an electric motor. The motor may be external or be an integral part of the compressor.

condensing unit: A portion of a split air- conditioning or refrigeration system that's mounted outside and contains the compressor, condenser, condenser fan motor, and controls for these components; most used today are air cooled. It takes the cool suction gas from the evaporator, compresses it, condenses it to a liquid, and forces it back to the evaporator.

conductor: A wire that's used for the path of electric flow. Most electric conductors are copper or aluminum.

constant discharge pressure: Maintaining the discharge pressure at a constant pressure; this is accomplished by controlling the amount of heat rejected by the condenser by controlling the con denser fan motors.

contactor: A device that opens and closes a set of electric contacts by the action of a solenoid coil; composed of a solenoid and the contacts.

contacts: The part of a relay that opens and closes to allow for the flow of electrical energy.

continuity: A complete path for electrons to follow in a circuit or component.

control circuit: A circuit that controls some load in the entire control system, whether it be a relay or contactor coil or a major load.

control relay: A relay that's used to control a circuit or circuits in an air-conditioning system.

current: Electrons flowing in an electric circuit, measured in amperes.

current electricity: Electricity that results from the electron being displaced and moving back to the atom.

current overload: An overload that opens a set of contacts on high current draw and allows them to close when the current draw has decreased. It usually is a pilot duty device.

current relay: A relay that's opened or closed by the starting current of an electric motor. The relay allows a starting capacitor and starting winding to drop out or drop in the starting circuit.

current-sensing lockout relay: A relay that will lock out a control system in the event of high current.

cut-in pressure: The pressure at which a pressure control will close, starting the device it's controlling. cut-out pressure: The pressure at which a pressure control will open, stopping the device it's controlling.

cycle: One complete cycle of alternating current is the production of a positive and negative peak.

D

de-energize: To stop the electron flow to an electric device.

defrost control: A control that's used to initiate the defrost cycle of a heat pump or initiate the defrost cycle in a commercial refrigeration freezer.

defrost cycle: A cycle of operation of a heat pump that's designed to defrost the outside coil during the heating operation.

defrost module: A solid-state module that's responsible for controlling the defrost of a heat pump. Defrost modules come in many different forms, such as the time/temperature module, which only considers one condition, or a demand module, which considers several conditions.

dehumidifier: An appliance that's used to remove humidity from the air.

delta system: A three-phase electrical supply system that's determined by transformer hookup. The delta system due to the transformer hookup gives two usable low-voltage legs plus a high leg. The delta system is used when a large number of three-phase loads are used.

delta transformer: A three-phase transformer that has the ends of each of its windings connected together to form a triangle. The delta transformer produces a high leg on one of its power legs.

delta winding: A winding layout of some three- phase motors, where the beginning of the windings is connected to the ending of the windings.

dielectric: The substance that's between the plates and fills the case of a capacitor. The substance is a nonconductor of electricity.

differential: The difference between the cut-in and cut-out point of a control. This can be applied to thermostats, pressure switches, and most controls.

digital meter: A meter that uses a digital display to indicate an electrical characteristic.

diode: A semiconductor that allows voltage to pass in only one direction.

direct current: An electron flow in only one direction; used in the industry only for special applications such as solid-state modules and electronic air filters.

direct drive: A method of transferring the rotating motion of a motor to a device that must be turned. This type of hookup connects the motor directly to the device that must be turned and rotates at the same revolutions per minute as the motor.

disconnect switch: A switch that's used to disconnect the power supply to a piece of equipment; it's sometimes referred to as a safety switch.

distribution center: An electric panel used to distribute electric supply to several places in a large structure; can be of fusible or circuit breaker design.

double insulated: A method used by appliance manufacturers that places a double insulating shield between the user and the appliance.

E

effective voltage: Alternating current, with its many reversals and peaks, never peaks at a constant value. The effective voltage is the working voltage of alternating current. The effective voltage is 0.707 times the peak voltage.

electric circuit: A path for electrons to follow; the circuit may be open or closed, depending on the position of its switches.

electric energy: Energy that's produced by a movement of electrons. The energy can be produced by chemical, light, thermal, or mechanical means.

electric control system: A control system that's operated by an electrical source. An example of an electric control system is the control of a window unit.

electrical resistance heater: A designed piece of wire that produces heat when supplied with electrical energy and usually manufactured to be inserted into an air flow. Many times resistance heaters are used as supplementary heaters in a heat pump system.

electric meter: A device used to measure some electrical characteristics of a circuit such as the volt age, amperage, resistance, or wattage.

electric power: The rate at which electricity is being used, measured in watts.

electric pressure: Another term used to refer to electromotive force, potential difference, and voltage. electric switch: A device that opens or closes to control some load in an electric circuit. It can be opened or closed by temperature, pressure, humidity, flow, and manual means.

electrical shock: A condition in which a person becomes part of an electrical circuit. Many times this condition causes serious injury or death.

electricity: Energy that's capable of producing an electron flow. An unbalanced condition that results when an electron can be easily displaced from an atom.

electrodes: The dissimilar metal conductors in a battery that produce a small difference of potential.

electrolyte: The chemical paste between the electrodes of a battery and some capacitors.

electromagnet: A magnet produced by coiling wire around a metal core.

electromechanical clock thermostat: A thermostat that can be used to set back the temperature at specific times.

electromechanical control system: A control system that uses electromechanical controls to maintain the temperature of the conditioned space.

electromotive force (emf): The difference of potential that forces electrons through a resistance.

electronic control system: A control system that uses electronics to control the temperature of a structure.

electronic module: A solid-state module that controls the operation of a system, equipment, or single function of a conditioned air system.

electronic self-diagnostic feature: A feature in a control system that automatically diagnoses problems in the heating and air-conditioning system.

electronically commutated motor: A variable speed motor that's driven by an inverter and is inter faced with the heating and air conditioning controls. The ECM is a three phase DC motor with a permanent magnet rotor.

electrons: Particles that orbit around the nucleus of an atom and have a negative charge.

element: A substance that has weight, takes up space, and cannot be broken down by chemical means.

energize: To apply voltage to an electric device.

energy efficiency ratio (EER): The means of measuring an air conditioner for its efficiency by stating how many Btu’ s of cooling are available from one watt.

F

factory-installed wiring: The wiring installed in a piece of equipment at the factory; usually the connections between the components in the control panel and the system components in the unit itself.

factual diagram: A wiring diagram that's a combination of the pictorial and schematic diagrams.

fan switch: A temperature-controlled switch that starts and stops a fan motor on a gas furnace depending on the temperature.

fault isolation diagram: A type of trouble shooting chart that isolates problems in a control system.

field of force: The area around a magnet that's affected by the strength of the magnet.

field wiring: The wiring that must be installed in the field by the installation mechanic.

flow diagram: A block diagram that outlines the operation of a heating and air-conditioning unit. flux: The magnetic lines of force of a magnet that connect the north and south poles of the magnet. free electron: Electrons that are easily removed from the outer orbits of atoms.

frequency: The number of complete cycles per second of alternating current.

full-load amperage: The amp draw of a load when operating at full load conditions.

fuse: A device that breaks a circuit when its ampere rating is exceeded: constructed of two ends or conductors with a piece of wire that will melt and break the circuit on an overload.

fusible disconnect switch: A disconnect switch used to interrupt the power supply to a load and also to provide fuse protection.

fusible load center: An electric panel that sup plies circuits with power and protects them with fuses.

gas furnace: A fossil fuel appliance that's designed to heat air and supply it to the structure.

gas pack: A unit that heats in the winter by using gas as its fuel and cools in the summer by using electric power.

gas valve: A valve that opens and closes upon a call for heat from the thermostat. Some gas valves have more than one valve built into the body. These additional valves are used for safety.

ground: A conducting connection between an electrical circuit or equipment and the earth. ground fault circuit interrupter (GFCI): An electrical device that will open a circuit, preventing current flow to the circuit when a small electrical leak to ground is detected.

G

grounded: The electrical condition that exists when a current-carrying conductor comes in contact with a ground.

grounding adapter: An adapter used between a grounded appliance and a nongrounded receptacle. This practice isn't recommended.

H

head pressure: The discharge pressure of a refrigeration system, sometimes called high-side pressure.

heat pump: A refrigeration system that reverses the flow of refrigerant in the normal refrigeration cycle, which allows the unit to cool in the summer and heat in the winter.

heater: An electric load that converts electric energy to heat.

hermetic compressor motor: A motor that's designed for single- and three-phase operation and is totally enclosed in a shell with refrigerant and oil.

hertz: The number of complete cycles per second of alternating current; more widely accepted than the term “frequency.” hopscotching: A troubleshooting procedure for electric circuits that's accomplished by jumping from one component to another.

hot surface ignition: A method of lighting a main gas burner with a hot surface igniter.

hot-wire relay: A relay that's opened or closed by a thermal element that senses the starting cur rent of the motor. The relay allows a starting capacitor or starting winding to drop out or drop in the starting circuit. This type of relay also has a built-in means of overload protection.

humidistat: A device that's used to control humidity; it uses a moisture-sensitive element to control a mechanical linkage that opens and closes an electric switch.

high-pressure switch: A pressure operated switch that opens or closes on a rise or fall in pres sure on the high side of a refrigeration system. This type of switch can be used as a safety control that would open on when the pressure reached an unsafe condition or operate some electrical component by closing on an increase of pressure.

I

ignition module: An electronic module that's designed to supervise the lighting of a pilot or main burner.

impedance: The sum of the resistance and reactance in an alternating current circuit.

indoor fan relay: An electric relay that starts and stops an indoor fan on cooling, electric-heating, and heat pump systems.

indoor fan relay package: A package that incorporates a control transformer, indoor fan relay, and low-voltage control terminal board.

induced magnetism: The magnetism induced around a current-carrying conductor.

inductance: A property of an alternating current circuit by which an electromotive force is produced in it by a variance in current.

inductive load: A load that starts with a larger ampere draw and reduces it as the load starts normal operation. The increase in the ampere draw initially is due to inductance.

inductive reactance: The opposition to the change in alternating current flow that produces an out-of-phase condition between voltage and amperage.

installation and service instructions: A writ ten set of instructions that explains the proper installation procedures and service procedures for a specific model of equipment. This set of instructions are usually packed with the equipment when shipped from the factory.

installation diagram: A diagram that shows little internal wiring but gives specific information as to terminals, wire sizes, color coding, and breaker or fuse sizes.

insulator: A material that retards the flow of electrons or electricity.

interlock: The action of stopping and starting a component only when another component has started. A good example of an interlock control isn't allowing a water chiller to operate until the chilled water pump has begun operation.

internal compressor overload: An overload that's embedded in the windings of a motor. Some internal overloads break the power to the motor directly, while others merely open a set of contacts that's wired into an electric control circuit.

internal pressure relief valve: A valve placed in the discharge side of a hermetic compressor that would open and relieve the pressure if it exceeded a certain point.

J-K

kilowatt-hour: The rate at which electric energy is being used at a specific time. Most electric utilities bill their customers in this method.

L

law of electric charges: Like charges repel and unlike charges attract.

light commercial air-conditioning system: Air-conditioning equipment that's used in the light commercial phase of the industry, usually 25 tons or less.

light-emitting diode: A diode that will produce light with electrical energy flows through it.

limit switch: A safety that's designed to open in the event of excessive temperature in an appliance.

line break overload: An overload that breaks the power going to the motor and is most commonly used on small motors.

line voltage: The voltage being supplied to the equipment at the power supply.

line voltage control system: A control system that utilizes line voltage to control an air-conditioning system or equipment.

line voltage thermostat: A thermostat that's used primarily to break line voltage to a load to control the temperature.

“live” electrical circuit: A circuit that's being supplied with electrical energy.

load: Electric devices that consume electricity to do useful work, such as motors, solenoids, heaters, and lights.

load analyzer: A device that analyzes the load of a structure and determines the correct action of a heating and cooling unit.

locked rotor amperes: The current a motor uses the instant it starts while the rotor is in a stationary position.

lockout relay: A high-impedance relay that has a normally closed set of contacts and is used to lock a control system out when a safety control opens. A lockout relay must be reset in order for the equipment to operate.

low-pressure switch: A pressure operated switch that opens or closes on a rise or fall of pressure on the low side of the refrigeration system. This type of switch can be used as a safety control, to stop loads in the event of low pressure or operating control, to operate loads to maintain a certain temperature.

low-voltage control system: A control system that uses low voltage, usually 24 volts, to operate the controls of an air-conditioning or control system. low-voltage thermostat: A thermostat that's designed to interrupt a 24-volt power supply to electrical loads depending on the temperature.

M

magnetic field: The area around a magnet in which the effect of the magnet can be felt.

magnetic overload: An overload device that senses the current draw of a load by the magnetic field produced, which is proportional to the current draw. The device will open a set of contacts on high current draws and allow them to close when the ampere draw returns to normal.

magnetic starter: A device that opens and closes its contacts when a solenoid is energized. A means of overload protection is provided. It is the same as a contactor except for the overload protection.

magnetism: The ability of two pieces of iron to be attracted to each other by physical means or electrical means.

matter: The substance of which all physical objects consist.

measurable resistance: The actual resistance of a circuit or component measured with an ohmmeter.

mechanical linkage: The linkage that connects the contacts to the armature, enabling the contacts to close or open when the coil is energized.

microfarad: The unit of measurement used to measure the strength of a capacitor.

module: An electrical device that's used to control one or more functions of a control system.

molecule: The smallest particle into which a sub stance can be divided and still maintain the proper ties of that substance.

molten-alloy relay: An overload device that opens a set of contacts by thermal energy. This type of device allows the temperature produced by the starting current of a load to be transferred to a molten-alloy device. When it reaches a certain temperature, it will melt the solder around the device, causing it to slip and open the contacts; when it cools it will harden again and the relay must be manually reset.

motor: A device used to create a rotating motion and drive components that require rotating motion. Electric energy is changed to mechanical energy by magnetism, which causes the motor to turn.

motor protection module: A solid-state module that's responsible for the protection of a large electric motor. This type of control usually has sensors mounted in the motor windings.

multistage control system: A control system that's used to control heating or cooling elements of an air-conditioning or heating system at different temperatures.

multistage thermostat: A thermostat that's used to control different stages of a heating and cooling system.

multizone: A heating and cooling unit that's equipped to condition more than one zone in a structure.

N

National Electrical Code: A set of standards published by the National Fire Protection Association that specifies the minimum standards that must be met for the safe installation of electrical systems.

negative charge: The result of electrons joining atoms.

neutron: The neutral particle in the nucleus of an atom.

nonfusible disconnect switch: A disconnect switch used only to interrupt the power supply to a load.

noninductive load: A load that has only resistive qualities with no inductive qualities. An electric heater and incandescent lighting are two common types of noninductive loads.

normally: A term that refers to the position of a set of contacts when the device is de-energized.

normally closed: The position of a set of contacts or other electric devices that are closed when the device is de-energized.

normally open: The position of a set of contacts or other electric devices that are open when the device is de-energized.

nucleus: The central part of an atom composed of protons and neutrons.

O

ohm: The amount of resistance that will allow one ampere to flow with a pressure of I volt.

ohmmeter: An electrical meter used to measure the resistance of a circuit or electric component.

Ohm’s law: The relationship between current, electromotive force, and resistance in an electric circuit: I = E/R?.

oil safety switch: A switch that's used to open the circuit when the oil pressure in a compressor is below an acceptable level.

one-function solid-state device: An electronic device that performs only one function such as an electronic time-delay module, defrost module, and anti-short-cycling module.

open: The condition that exists in an electrical circuit when there is no complete path.

open circuit: A circuit without a complete path for electrons to follow.

out of phase: A condition in which the voltage and current are not working together.

overload: A device that's used to detect a high ampere draw of some electric load and break the controlling circuit, stopping the load.

overshoot: The additional heating or cooling that has been delivered to the conditioned space after the thermostat contacts have opened.

P

packaged air-conditioning unit: A system built with all components in one unit except for the field wiring.

parallel circuit: An electric circuit that has more than one path for current flow.

peak voltage: When the voltage reaches its peak in an alternating current circuit.

permanent magnet: A piece of material that's magnetic by physical means. Iron, nickel, cobalt, and chromium are materials that can easily be magnetized and will maintain their magnetism for a period of time.

permanent split-capacitor motor: An electric motor, widely used in the industry, that has a moderate starting torque and good running efficiency.

phase: The number of currents alternating at different times in an alternating current circuit.

pictorial diagram: A wiring diagram that shows the actual internal wiring of a unit, much like a picture taken of a control panel. It is also called a line or label diagram.

pilot: A flame that's standing or established to light the main burner of a gas valve.

pilot assembly: An assembly that holds the pilot burner and the method of ignition.

pilot duty: A term used to refer to an electric device that indirectly controls a major load because of its large ampere draw but controls it directly through a device that's capable of carrying the load. pilot duty overload: An overload that senses the load of the circuit or power-consuming device and breaks a set of contacts that's isolated from the sensing element.

pneumatic control system: A control system that uses air to control the temperature of a structure. pole: One set of electric contacts either in an automatic device or a manual switch. Electric devices such as relays, contactors, switches, and breakers can be purchased with one or many poles.

positive charge: The result of electrons leaving an atom.

potential coil: A coil energized by a voltage being applied to it. It can be designed to operate on 24, 110, 208/240, or 480 volts. These coils are used on relays, contactors, and magnetic starters.

potential difference: Two points that have a difference in electric charge; the electric difference between two points in an electric circuit.

potential relay: A relay that uses the back electromotive force of a motor to drop out the starting apparatus when the motor reaches 75% of full speed.

power circuit: An electrical circuit that supplies electrical energy to a load or equipment.

power factor: The ratio of true power to apparent power, usually expressed as a percentage.

pressure switch: A device that opens or closes a set of contacts when a certain pressure is applied to the diaphragm of the switch.

primary control: An electrical control used to supervise the operation of an oil burner.

programmable thermostat: A thermostat that can be programmed to set up and set back the temperature of the structure for certain periods of the day or week.

proton: A positively charged particle in the nucleus of an atom.

pump-down control system: A control system that closes a solenoid to allow the compressor to pump all the refrigerant from the low side of the sys tem into the high side. This system is used on large air-conditioning systems and some commercial refrigeration systems.

push-button switch: A switch that can be opened or closed by pressing buttons on the switch. Push-button switches come with a wide variety of purposes and labeling.

Q-R

range: The operating ranges or limits of a control.

reactance: The resistance that alternating current encounters when it changes flow.

rectifier: A device that will allow electrical current to pass in one direction but stops electrical current from flowing in the opposite direction. This device is commonly used to rectify AC voltage to DC voltage.

relay: A device that opens and closes a set of contacts when its coil is energized. The relay is much like the contactor except for its smaller size.

relief valve: A device that will open on a rise in pressure and release pressure to return a closed sys tem to a safe operating condition and close when the pressure has decreased.

reset point: The point at which an electrical control will close its contacts after an unsafe condition has corrected itself.

resistance: The opposition to the flow of electrons. resistive load: See noninductive load. reversing valve: A valve used to reverse the refrigerant flow in a heat pump.

rooftop unit: A heating and cooling unit that conditions a structure; it's mounted on the roof after adequate reinforcement has been built into the roof.

rotor: The rotating part of an electric motor. running (oil-filled) capacitor: An electric device that's used to momentarily store electrons and create a second phase in the starting winding circuits of single-phase motors. This type of capacitor is designed to stay in the circuit whenever the motor is running as a means of heat dissipation. safety device: Any device that's in a control system for the purpose of making the operation of a major load safer.

S

schematic diagram: A diagram that lays out the control system circuit by circuit and is composed of symbols representing components and lines rep resenting their interconnecting wiring.

seasonal energy efficiency ratio (SEER): An equipment efficiency rating that takes into account the startup and shut-down for each cycle.

semiconductor: A conductor whose electrical conductivity is between that of an insulator and a metal.

sensor: A device that produces a signal that changes with a temperature change.

sequencer: An electrical device that's used to control electric resistance heaters. Sequencers can have up to five sets of contacts that open and close at different time intervals. In most cases, sequencers are 24 volts.

series circuit: An electric circuit that has only one path for electron flow.

series-parallel circuit: A combination of series and parallel circuits.

set point: The point at which a control will open and close.

shaded-pole motor: An induction type of motor that does not incorporate an ordinary type of starting winding. It uses a band on one side to obtain a short- circuit effect that produces a rotating magnetic field. This motor has a low starting torque.

short: The condition that exists in an electrical circuit when there is no resistance.

short circuit: An electric circuit that has no resistance.

short-cycling: A term used to refer to a condition that occurs when a load is stopping and starting too frequently.

signal light: A light that's used to show when some electric component or circuit's energized by illuminating the light.

sine wave: A graphical representation of alternating current; a graph showing the sine function of all angles from 0 to 360 degrees.

single phase: An electrical power supply that supplies two hot legs of electrical energy to a circuit.

sleeve bearing: An antifriction device that allows free turning and support of the rotating member of a device. It consists of a solid piece of bronze or babbit that's round and drilled to the diameter of the shaft. The bearing is sometimes called a plain bearing or bushing.

sliding armature: An armature that mounts between two slots in a contactor frame and moves up and down the slots when the contactor is energized.

snap action of a thermostat: The closing of a set of contacts of a thermostat with a snapping motion rather than with a light contact.

solenoid: A device that, when energized, will create a magnetic field and cause some action to an electric component. It opens and closes to control some element of a heating, cooling, and refrigeration control system.

solenoid valve: A valve that opens or closes by a solenoid coil being energized to pull a steel core into the magnetic field of the solenoid.

solid-state relay: An electronic device constructed from semiconductor material, used to control electrical loads.

spark ignition: A method of creating a spark, igniting a gas pilot or main gas burner.

split-phase motor: An electric motor that has a running and starting winding. This is an induction type of motor.

squirrel cage rotor: The rotating part of an electric motor; its name is derived from the similarity of its appearance to a squirrel cage. This type of rotor is used in split-phase, capacitor-start, shaded-pole, and three-phase motors.

stack switch: A primary control that supervises the operation of an oil burner by sensing heat in the stack after the oil burner has ignited.

staged system: A system that has more than one mode of heating or cooling operation.

staging thermostat: A thermostat that's designed to open and close more than one set of contacts to control several modes of heating or cooling operation.

star transformer: A three-phase transformer that has the ends of each winding connected to a common point. The star transformer produces a balance of all hot legs to ground.

star winding: A winding layout of some three-phase motors in which the ends of the windings are connected.

starting capacitor: An electric device that's used to momentarily store electrons, creating a second phase in the starting windings of single-phase motors. This type of capacitor is designed to stay in the circuit only a short period of time.

starting relay: A relay that's used to energize or de-energize the starting components of a single- phase motor.

static electricity: Electricity that results from the electron being displaced and not returning to the original atom; usually results from friction.

stator: The stationary part of an electric motor.

swinging armature: An armature used in a contactor that's mounted on a line and moves up and down in a swinging motion.

switch: A device for making, breaking, or changing the connection in an electric circuit.

system lag: The difference in temperature between the point at which the thermostat closes and the point at which the thermostat starts to rise or fall.

T

thermal overload: An overload device that senses the current draw of a load by the heat produced, which is proportional to the current draw.

thermal relay: An overload device that deter mines current flow and opens a set of pilot duty contacts when an overload is indicated.

thermistor: A semiconductor that has a temperature coefficient of resistance that corresponds with a designated temperature. This device is widely used as a signal device in a control circuit.

thermocouple: A device that's made of two dissimilar metals that produce a small voltage when heated.

thermostat: A device that responds to a temperature change by opening or closing a set of electric contacts.

thermostat controlling element: The portion of a thermostat that reacts to temperature change by opening or closing the contacts through a mechanical linkage. The two types of elements are bimetal and bulb.

three phase: An electrical power supply that supplies three hot legs of electrical energy to a circuit.

three-phase motor: An induction type of motor that has a very high starting torque and requires no special starting apparatus. The motor must be operated on a three-phase current.

three-prong plug: A electrical plug on an appliance that has a ground. The round or oval prong on the plug is the ground.

throw: This refers to the number of positions of the movable contacts that will complete a circuit.

time clock: A clock that opens and closes contacts at specific time(s). Time clocks can be 24-hour or 7-day clocks.

time-delay relay: A relay that delays its closing for a certain period of time.

torque: The starting power of an electric motor.

transformer: A device that decreases or increases the incoming voltage to the desired voltage.

transistor: A semiconductor device used for the control and amplification of a signal from one circuit to another circuit.

triac: A bidirectional electronic component that has an on or off and is used to control AC voltage.

trip-out point: The point at which an electrical control will open its contacts in the event of an unsafe condition.

troubleshooting chart: A chart furnished by equipment manufacturers to guide the technician in troubleshooting a specific type of equipment.

troubleshooting tree: A type of troubleshooting chart that follows a sequence to troubleshoot a control system.

U-V

varistor: A semiconductor with a voltage-sensitive resistance.

V-belt: The belt that connects the pulleys of a motor and the device that must be rotated and transfers the rotating motion from the motor to the device. V-belts can be purchased in several widths and almost any length.

volt: The amount of electric pressure required to force one ampere through a resistance of one ohm.

voltage: The difference in electric potential between two points.

voltage drop: The amount of voltage lost through any type of switching device or conductor.

voltage spike: A sudden and temporary increase of voltage that can damage electronic circuits.

voltmeter: An electric meter used to measure voltage.

W-Z

water chiller: A refrigeration system that cools water that's pumped into other parts of the system to maintain the desired condition in a specific area.

water-cooled packaged unit: A unit that's made in one complete unit with a water-cooled con denser as an integral part.

watt: One ampere flowing with a pressure of one volt. The unit measurement of power.

wiring diagram: A systematic method of laying out the wiring that's interconnecting the control components within the control system; three types are schematic, pictorial or line, and installation.

wye system: A three-phase electrical supply sys tem that's determined by transformer hookup. The wye system due to the transformer hookup gives three usable low-voltage legs. The wye system is used when a large number of low-voltage, single- phase circuits are needed.

wye transformer: A three-phase transformer that has a common junction point and forms a Y. This transformer hookup allows for a completely balanced load when using all hot legs and ground.

zone: A section of a structure that has a heating and cooling load.