Level 1 Mod 3

Electromagnet

A coil of wire wrapped around a soft iron core. When current flows through the coil, magnetism is created.

Continuity

A continuos current path. The absence of continuity indicates an open circuit.

In-line ammeter

A current-reading meter that is connected in series with the circuit under test

Insulator

A device or substance that inhibits the flow of current; the opposite of conductor

Rectifier

A device that converts AC voltage to DC voltage

Relay

A magnetically operated device consisting of a coil and one or more sets of contacts

Conductor

A material through which it is relatively easy to maintain an electrical current

Digital meter

A meter that provides a direct numerical reading of the value measured

Analog meter

A meter that used a needle to indicate a value on a scale

Line duty

A protective device connected in series with the supply voltage.

Pilot duty

A protective device that opens the motor control circuit, which then shuts off the motor.

Thermistor

A semiconductor device that changes resistance with a change in temperature.

Inrush current

A significant rise in electrical current associated with energizing inductive loads such as motors.

Ladder diagram

A simplified schematic diagram in which the load lines are arranged like the rungs of a ladder between vertical lines representing the voltage source.

Multimeter

A test instrument capable of reading voltage, current, and resistance. Also known as a volt-ohm-milliammeter (VOM).

Ammeter

A test instrument for measuring electrical current

Arc

A visible flash of light and the release of heat that occurs when an electrical current crosses an air gap.

Clamp-on ammeter

An ammeter with operable jaws that are placed around a conductor to sense the magnitude of the current flow.

Direct current (DC)

An electric current that flows in one direction. A battery is a common source of D.C. voltage

Alternating current (AC)

An electrical current that changes direction on a cyclical basis

Resistance

An electrical property that opposes the flow of current through a circuit. Resistance (R) is measured in ohms.

Solenoid coil

An electromagnetic coil used to control a mechanical device such as a valve or relay contacts.

Ground fault

An unintentional, electrically conducting connection between an energized conductor of an electrical circuit and another conductor, such as metal objects, earth, or an equipment frame. The fault current passes through the grounding system, as well as a person or other conductive surface in the path.

Contactors

Control devices consisting of a coil and one or more sets of contacts used as switching devices in high-voltage circuits.

Loads

Devices that convert electrical energy into another form of energy (heat, mechanical motion, light, etc.). Motors are the most common significant loads in HVACR systems.

Time-delay fuses

Fuses with a built-in time delay to accommodate the inrush current of inductive loads.

Motor starters

Magnetic switching devices used to control heavy-duty motors.

Inductive

Of a load, able to become electrically charged from being near another electrically charged body, or to become magnetized by being within an existing magnetic field. The process itself is called induction.

Ampere (A)

The basic unit of measurement for electrical current, represented by the letter A.

Ohms

The basic unit of measurement for electrical resistance

Short circuit

The bypassing of a load by a conductor, causing a very high current flow.

Voltage

The driving force that makes current flow in a circuit. Voltage, often represented by the letter E, is measured in volts. Also known as electromotive force (emf), difference of potential, or electrical pressure.

Power

The rate of doing work, or the rate at which energy is dissipated. Electrical power is measured in watts.

Current

The rate or volume at which electrons flow in a circuit. Current (I) is measured in amperes

Watts (W)

The unit of measure for power consumed by a load.

Volts (V)

The unit of measurement for voltage, represented by the letter V. One volt is equivalent to the force required to produce a current of one ampere through a resistance of one ohm.

Transformer

Two or more coils of wire wrapped around a common core. Used to raise and lower voltages.