Basic Electricity
The electrical force or electrical pressure created by a potential difference in atomic charges between two points. Also called electromotive force.
What is voltage?
A condition in which a device or ungrounded metal part becomes electrically hot or live. This is a dangerous condition in which a short circuit to ground that is waiting to happen. This may also be called a short to ground.
What is a ground fault?
An electromagnetic device composed of a coil of wire wrapped around a case with a movable iron core that is called a plunger. These are commonly fitted to a valve body and used to control the opening and closing of valves.
What is a solenoid?
The speed (RPM) of the rotating magnetic field in an electric motor’s stator. A motor runs at synchronous speed if the speed of the rotor equals the speed of the stator’s rotating magnetic field.
What is synchronous speed?
A special high-impedance relay that keeps a circuit from restarting when any of the safety controls in the circuit have opened. Power to the coil must be interrupted to reset the lockout relay contacts and return the system to normal operation.
What is a lockout relay?
A single electrical meter that can measure multiple electrical variables, such as voltage, current, and resistance. Also called volt-ohm-milliammeter (VOM).
What is a multimeter?
A kit sized to a specific voltage that is used to start a stuck single-phase compressor motor. The kit consists of a capacitor, a PTC or potential relay, and wires.
What is a hard start kit?
The voltage applied across an electrical load that is causing current to flow through it. Intentional ones are good, while unintentional ones can cause circuit problems.
What is a voltage drop?
The earth to which an electrical system connects.
What is ground?
A device that converts an input signal from one form of energy to an output signal of another form of energy.
What is a transducer?
The work performed by a twisting or turning action, such as a rotating motor shaft.
What is torque?
A safety control device used to turn off the compressor before dangerously high pressure is reached.
What is a high pressure motor control?
An instrument used to provide a direct reading of the power factor in an electrical circuit.
What is a power factor meter?
A motor bearing lubrication system in which a brass ring rests on the motor shaft and dips into the oil well below as the shaft turns to lubricate the bearing.
What is a slip ring lubricating system?
A unit of electromotive force. One is the amount of electromotive force required to send one ampere of current through a resistance of one ohm.
What is a volt?
The neutral wires connected to a grounded transformer to create a return path in an electrical circuit.
What is a grounded conductor?
A solid-state device with three terminals that conducts current in both directions. Current must be applied to its gate circuit in order to trigger conduction. It will only stop conducting when current drops below its preset holding current threshold.
What is a triac?
A controller that changes the speed of a motor by varying the frequency of the electrical signal supplied to the motor.
What is a variable frequency drive (VFD)?
A control device that reacts to the low-side pressure it senses by closing an electric switch on a rise to a preset pressure (cut-in setting) and opening that switch on a drop to a preset pressure (cut-out setting).
What is a low pressure motor control?
An electrical wiring diagram that is used primarily in service or installation manuals to illustrate how electrical devices are connected in a unit. They also show the approximate physical location of devices in a unit.
What are Pictorial diagrams?
An overload protection device that monitors the voltage of each phase of a three-phase motor’s power supply. A phase loss monitor opens the motor circuit if one of the phases blows a fuse or opens a circuit breaker.
What is a phase loss monitor?
Electromagnetic device used to transfer an alternating current from one coil of wire to another through a magnetic field.
What is a transformer?
An overcurrent electrical protection device containing a metal conductor in series with an electrical circuit that is designed to conduct a certain amount of current before it melts to open the circuit.
What is a fuse?
A layered, three-terminal semiconductor device that is used to either switch or amplify an electrical signal.
What is a transistor?
An induction motor that has three sets of stator windings that are energized by three-phase power. Each set of windings is connected to one phase of the three-phase power source.
What is a three phase motor?
A pressure-sensitive element, such as a diaphragm or bellows, that is set to shut down the compressor in the event of refrigerant loss or an evaporator freeze-up.
What is a low pressure safety control?
An instrument used to measure the potential difference, or voltage, between two points in an electrical circuit.
What is a volt meter?
A high value resistor that slowly discharges a capacitor when power to the capacitor’s circuit is turned off. When electrical voltage is applied during the On cycle, a bleed resistor acts as a virtual open switch (as if it was not even present in the circuit).
What is a bleed resistor?
A cylindrical piece of conductive material used in an ac electrical generator to transfer the electricity from the wire loop (rotor) to the brushes.
What is a slip ring?
An electrical problem that results when a conductor routes current around a component or an electrical load instead of through it. With no electrical load, a short circuit’s current value is very high.
A diode setup that does not allow current to flow through the diode. The negative terminal of a dc power supply is connected to the anode, and the positive terminal is connected to the cathode.
What is reverse bias?
Stator windings that are used for motor starting and additional torque in single-phase induction motors. They are made of smaller diameter wire than run windings, which gives them a higher resistance.
What is a start winding?
An electronic relay that uses a PTC thermistor to control a motor circuit by increasing its resistance as it senses high ambient temperature.
What is a positive temperature coefficient (PTC) relay?
An ammeter that senses and measures only alternating current based on the magnetic field produced by an alternating current as it flows through a conductor. They clamp around a single conductor using movable jaws and do not require breaking the circuit for measurements.
What is a clamp-on ammeter?
The accumulation of an electric charge that results when an object picks up negative charges, such as when rubbing against another object. In maintaining air quality, static electricity is used by electronic air cleaners, which build up an electric charge on particles in the air.
What is static electricity?
The value used to equate the heat produced by an alternating current to a direct current value that would produce the same amount of heat.
What is root mean square (rms)?
A three-terminal semiconductor switching device that conducts current in only one direction. The device’s breakover voltage must be exceeded or current must be applied to its gate circuit in order to trigger conduction.
What is a silicon-controlled rectifier?
The stationary part of an electric motor that is attached to the inside of the motor housing. It can also be called the frame.
What is a stator?
The voltage required in a motor’s start winding to energize a potential relay coil, which drops the start capacitor out of the circuit. It is typically generated when a motor reaches around three-fourths of its normal operating speed.
What is Pickup voltage?
An electrical line diagram that shows the devices and connections in a circuit arranged in the order that they activate during circuit operation. The vertical lines in the diagram identify the power supply, and the horizontal lines contain the various devices and controls located in the circuit.
What is a ladder diagram?
An electrical circuit in which current has only a single path to follow.
What is a series circuit?
A condition in which too much current flows through an electrical circuit. It can lead to excessive heat generation and result in fire or deterioration of electrical insulation. The current is not as high as in a short circuit.
What is overload?
The concept underlying the production of thermoelectricity. When heat is applied to the junction of two dissimilar metals (a thermocouple’s hot junction), the temperature difference between the two metals produces a voltage.
What is the Seedbeck effect?
A capacitor used to provide starting torque during the start-up of some single-phase motors. It is dropped out of the motor circuit after the motor reaches full speed.
What is a start capacitor?
A control device that reacts to the low-side pressure it senses by closing an electric switch on a rise to a preset pressure (cut-in setting) and opening that switch on a drop to a preset pressure (cut-out setting).
What is a low pressure motor control?
An electrical insulation tester that is used to detect current leaks or possible areas of insulation failure along conductors. It measures resistance by applying a known voltage supplied by the meter.
What is a megohmmeter?
An electrical circuit that includes a combination of series and parallel circuits.
What is a series-parallel circuit?
An electrical protection device that detects imbalances between ungrounded and grounded conductors of a circuit. It opens the electrical circuit when equipment connected to it is defective, misused, or improperly grounded.
What is a ground fault circuit interupter (GFCI)?
A device that detects and responds to a stimulus, such as a change in temperature or pressure. Most are electronic devices and used in control circuits.
What is a sensor?
The motor terminal on a single-phase hermetic compressor that connects to one end of the start winding. The opposite end of the start winding is connected to the common terminal.
What is the starting terminal?
An electronic circuit used to detect changes in a thermistor’s resistance. A temperature change causes the resistances in the bridge to become unbalanced, which alters the bridge’s output voltage and sends a signal to the controller.
What is a Wheatstone bridge?
An ammeter that is connected to a circuit with leads to measure a circuit’s current. must break the circuit to be connected in series to take measurements.
What is an In-line ammeter?
The coil of wire in a transformer in which voltage is induced by the changing magnetic field created by alternating current passing through the primary coil.
What is a secondary coil?
A condition in which the applied voltage from a power source is unintentionally reduced in a circuit. This may be down to a level that is too low for safe use on electrical loads in the circuit.
What is an unintentional voltage drop?
A semiconductor device that changes its ability to conduct electricity or produces an electrical signal in response to visible, infrared, or ultraviolet light.
What is a photoelectric device?
A single-phase induction motor that uses the different inductance values of its start winding and run winding to produce phase splitting and achieve initial rotation.
What is a split phase motor?
A type of control system in which the controller sends commands to a controlled device with no detected information from the conditioned space being returned to the controller.
What is an open-loop control system?
A material or substance that is ordinarily an insulator, but can be made to conduct electricity. It's conductivity may be controlled by light, pressure, temperature, and other devices.
What is a semiconductor?
A mathematical relationship among power, voltage, and current in an electrical circuit (P = I × E).
What is Watt's Law?
An electrical switch that operates under the control of an outside electrical signal. They are commonly used to start or stop other system components, such as motors.
What is a relay?
A single-phase motor that uses shaded field poles instead of a start winding to produce starting torque. One-third of each stator pole is split from the rest of the pole and wrapped with a copper band or copper wire.
What is a shaded pole motor?
A fuse that will not blow unless an overload condition exists for a certain period of time, typically ten seconds. Also called a dual-element fuse.
What is a time delay fuse?
An electrical or electronic component used to offer a specific level of resistance in a circuit.
What is a resistor?
An instrument used to measure the true power, or wattage, used by a circuit or an electrical load. It is connected in series with the circuit or load being measured.
What is a wattmeter?
A device’s direct relation response of increasing a certain characteristic as temperature increases and vice versa. For example, a thermistor of this type increases in resistance as temperature increases and vice versa.
What is a positive temperature coefficient (PTC)?
In an electric motor, an axle-mounted unit that rotates as the polarities of the stator’s field poles change. In some cases, it can also be called the armature.
A relay that uses electronic components (such as transistors, silicon-controlled rectifiers, or triacs) rather than mechanical components to switch circuits on and off. SSRs are used to start single-phase motors and are often referred to as electronic relays.
What is a solid state relay (SSR)?
An electrical property that measures a material’s opposition to the flow of electrons through it.
What is resistance?
A type of electrical power that has three alternating voltage signals in a single circuit. The three separate voltage signals alternate in three separate phases, which creates the effect of providing constant power.
What is three phase?
A meter used for measuring electrical resistance in an electrical circuit. It may also be used to check for short circuits, circuit continuity, and ground faults.
What is an ohmmeter?
The motor terminal on a single-phase hermetic compressor that connects to one end of the run winding. The opposite end of the run winding is connected to the common terminal.
What is the running terminal?
A fluid that vaporizes at a low temperature. Volatile fluids are used in sensing bulbs due to their ability to change pressure in response to changes in temperature.
What is a volatile fluid?
An electrical circuit in which current can flow to and from the power source along more than one path.
What is aparallel circuit?
A standardized system of designating wire size based on a wire’s diameter. For sizes 18 AWG to 1 AWG, the wire diameter increases as the AWG number decreases. For larger aught (/0) sizes, wire size increases as the numbers increase.
What is American Wire Gauge (AWG)?
A device’s inverse relation response of decreasing a certain characteristic as temperature increases and vice versa. For example, a thermistor of this type decreases in resistance as temperature increases and vice versa.
What is a negative temperature coefficient (NTC)?
A normally closed electrical switching device mounted on the end of a motor shaft that disconnects the start windings from the motor circuit. The switch is opened and closed by centrifugal force, which increases as motor speed increases.
What is a centrifugal switch?
A device that reacts to the heat it senses by closing or opening an electric switch to start or stop the operation of a motor.
What is a temperature motor control?
A mathematical relationship among voltage, current, and resistance in an electrical circuit (E = I × R).
What is Ohm's Law?
A circuit’s calculated power value (P = I × E), which does not take into account the effects of inductive reactance or capacitive reactance. The value is calculated in volt-amperes (VA).
A solid-state device composed of a P-type material and an N-type material. Electrons will flow through a diode in only one direction, from the cathode to the anode. It functions as a check valve for electrons.
What is a diode?
According to the NEC, operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest. Motors that are this are rated by how long they can safely run with a full load within 9°F (5°C) of their rated ambient temperature. These ratings are 5, 15, 30, or 60 minutes.
What is intermittent duty?
The coil of wire in an electrical transformer that is connected to the ac electrical source. As alternating current passes through this coil, it creates a magnetic field that induces alternating current in the secondary coil of the transformer.
What is a primary coil?
An electrical protection device that automatically opens a circuit when the current exceeds a predetermined level. The increased magnetic effect of the current surge causes a spring-loaded switch to trip and break the circuit. A circuit break can be reset for continued use, while a blown fuse must be replaced. An overcurrent electrical protection device that automatically opens a circuit when the current exceeds a predetermined level. The increased magnetic effect of the high current causes a spring-loaded switch to trip and break the circuit.
What is a circuit breaker?
An electronic component that functions as the control center of a system. It is capable of accepting information, storing it, and reacting in some preset way.
What is a microprocessor?
A single-phase induction motor that uses a single run capacitor in series with the start winding throughout the motor’s entire operation. It does not use a centrifugal switch or relay to switch off any capacitors or windings.
What is a permanent split capacitor (PSC) motor?