Electrical Instruments 251

AC

Alternating Current. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction 60 times a second, or 60 hertz, in the U.S.

alternating current

AC. A current formed when electrons flow in a one direction and then the opposite direction. Alternating current usually reverses direction 60 times per second.

ammeters

A device that measures amperes in an electrical circuit. An ammeter converts a magnetic field into a reading of electric current.

amperage

A measurement that indicates the amount of current flowing in a circuit. Amperage is measured in amperes (A), or amps.

amperes

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amperes are also called amps.

amps

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amps are also called amperes.

analog

A category of meter with a readout that uses dials with scales inscribed on them to display dimensions on the mill. Analog measurement is less precise than digital readout.

circuits

A completely enclosed path for electrical current. An electrical circuit usually includes a source, path, load, and control.

clamp ammeters

An electrical instrument that detects amperage in a circuit through a clamp placed around an energized wire. Clamp ammeters are used to detect high amperage.

common

C. A terminal on a wattmeter. The common terminal connects to the main terminal on the wattmeter.

constant

A variable or number that does not change. A voltage reading should be constant when a power supply is known.

continuity

The state of having a complete path to accommodate the uninterrupted flow of electricity. Continuity in a circuit can be checked by an ohmmeter.

current

I. The flow of electricity through a circuit. Current is measured in amperes or amps (A).

DC

Direct current. Electricity that travels in only one direction. Direct current never reverses the direction of current flow.

digital

A type of testing instrument that uses a numerical readout to display readings. Digital instruments are often more precise than analog instruments.

digital multimeters

DMM. A device that can measure voltage, current, or resistance. Digital multimeters are the most versatile and commonly used meters used today for electrical maintenance.

direct current

DC. Electricity that travels in only one direction. Direct current never reverses the direction of current flow.

directly proportional

A constant ratio between two values in which one value changes in the same way as the other. If values are directly proportional, it means that, when value A increases, value B also increases, and if value A decreases, value B decreases.

electric shock

The flow of electricity through the body. Severe electric shock can be fatal.

electrical potential

The electromotive force or pressure, which is called voltage. Potential between two points is measured by a voltmeter.

energy

The ability to do work. Energy is measured in kWh and expressed as the product of power and time.

frequencies

A measurement of the number of times something cycles in one second. Frequencies, such as that of AC electricity, are measured in hertz (Hz).

geared motor

A powered device that moves a gear, which in turn moves other gears in a gear train. A geared motor in an analog kilowatt-hour meter turns the indicators to give a value of electricity used over time.

ground

A source of zero electrical potential, such as the earth or another large conducting body. A ground absorbs electrical currents.

in parallel

A circuit configuration in which current flows through separate components in a circuit simultaneously because there is more than one path for current to flow. A voltmeter is connected in parallel to a circuit.

in series

A circuit configuration in which current passes through all components one after another because there is only one path for current to flow. An ammeter is connected in series with a circuit.

indicators

Discs with numbers ranging from 1 to 9 that give a value of the electricity used over time on a kilowatt-hour meter. Indicators turn in opposite direction from the indicators on either side of them.

infinite

Having no upper limit. Infinite ohms on an ohmmeter indicate a perfect insulator.

insulation

The state of being able to resist the flow of electricity. Insulation of voltmeter leads can prevent electric shock when used properly but is only guaranteed up to a certain level of current.

insulator

Material that does not allow for the easy flow of electricity. Insulators are used to protect conductors from excess heat and protect employees from electric shock.

kilowatt-hour

kWh. A unit that measures the use of electrical energy over time. Kilowatt-hours measure the power consumption in multiples of 1,000 watts per hour.

kilowatt-hour meter

A device that measures large amounts electricity used by a circuit over time. Kilowatt-hour meters track large power outputs in units of 1 kilowatt, or 1,000 watts, per hour.

kilowatts

kW. A unit of measurement for the power being used in a circuit. A kilowatt is equal to 1,000 watts.

leads

A conductive device within a circuit to which other components can be attached. A lead has either a negative or positive charge.

line

L. A terminal on a wattmeter. The line connects to the circuit that is being powered.

live

Electrically charged or energized. Live components carry electricity and present a risk of electric shock.

load

A component in a circuit that converts electrical energy into light, heat, or mechanical motion. Examples of loads are motors, appliances, and light bulbs.

magnetic field

The area in and around an energized conductor in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

main

M. A terminal on a wattmeter. The main terminal connects to the energized terminal on a power supply.

meters

A device that measures electricity. Meters can be analog or digital and measure many different values, including voltage (V), amperage (A), and wattage (W).

milliammeters

A device used to measure small electrical currents. Milliammeters express measurements in milliamperes, or thousandths of an ampere.

multimeter

A device that combines the functions of an ammeter, voltmeter, and ohmmeter. Multimeters can be digital or analog.

negative terminal

A connecting point in a circuit that has a negative charge. Negative terminals and positive terminals are attached to wires, which creates an electrical connection.

ohmmeters

Ohmmeters have their own power supply and attach to a de-energized circuit.

ohms

Ω. A unit of measurement for electrical resistance. Ohms indicate the amount of resistance in a circuit.

Ohm's law

The law that describes the relationship between voltage, amperage, and resistance. Ohm's Law states that voltages is equal to the current, measured in amperes, multiplied by the resistance, measured in ohms.

oscilloscopes

A device that produces a visual trace of a voltage or current wave shape. Oscilloscopes display AC waves.

overload

A level of current that exceeds the recommended level for a device or circuit but is less than the level of a short circuit. Overload is not detected by some wattmeters because they are not rated to measure large amounts of current.

perfect conductor

A material that allows a completely free flow of electrons. Perfect conductors have zero resistance.

perfect insulator

A material that does not allow any flow of electrons. Perfect insulators have infinite resistance.

personal protective equipment

PPE. An article of clothing or a device worn to minimize exposure to hazards and prevent injury. PPE for electrical work may include gloves and rubber-soled footwear.

picoammeters

A device used to measure small electrical currents. Picoammeters express measurements in picoammeters, or trillionths of an ampere.

polarity

Having a positive or negative charge. Polarity determines the direction in which current tends to flow.

positive terminal

A connecting point in a circuit that has a positive charge. Positive terminals and negative terminals are attached to wires, which creates an electrical connection.

power

P. The rate at which electricity is transferred within a circuit. Power is the product of current and voltage and is measured in watts (W).

probe ammeters

An electrical instrument that detects amperage in a circuit through probes that are touched to a circuit’s positive and negative wires. Probe ammeters are used to detect low amperage.

probes

A device attached to an electrical testing instrument that uses a conductive tip to connect to an electrical component. Probes connect to conductors and terminals.

resistance

R. The opposition to current flow. Resistance is measured in ohms (Ω).

resistor

A device that controls electric current. The resistor in an ammeter restricts current from flowing freely though a circuit so that the meter has enough current to measure without becoming overloaded.

short

The condition in which current takes a shorter, unintended path between two conductors. A short causes excess current flow.

short circuits

An interruption in the intended flow of electricity, especially when current flows without reaching the intended device. Short circuits cause excess current flow.

shunt

A low-resistance connection between two points in an electric circuit that forms an alternative path for a portion of the current. Shunts allow ammeters to produce accurate readings in a much wider rangefor much larger currents.

solenoid

A coil of wire that generates a force when an electrical current is applied. Wiggies use solenoids to detect voltage.

solenoid voltmeter

A testing device that vibrates when a current is detected. Solenoid voltmeters, or wiggies, are small and durable but can be replaced by more versatile and safer digital multimeters.

terminals

A conductive component on an electrical device to which other components can be attached. Terminals on a wattmeter connect to other terminals or devices.

troubleshooting

A systematic approach to solving problems quickly and efficiently. Troubleshooting often involves a logical process of elimination to identify the source of a problem.

voltage

E. A measure of electrical pressure or potential known as electromotive force. Voltage is measured in volts.

voltage

V. A terminal on a wattmeter. The voltage terminal connects to the neutral wire on a power source and to the circuit being powered.

voltmeters

A device used to measure voltage. Voltmeters measure voltage between two separate points on a circuit.

volt-ohm-milliammeters

VOM. The most common setup of a multimeter. VOMs combine the functions of voltmeters, ohmmeters, and milliameters.

volts

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts measure voltage, which is also known as electromotive force.

watt-hour meter

A device that measures the electricity used by a circuit over time. Watt-hour meters track power output in watts per hour.

wattmeter

A device that accounts for both current and voltage when used to measure electrical power. A wattmeter typically has four terminals.

watts

W. A unit used to measure wattage or electrical power. To exist, watts require a change in energy.

Watt's Law

A law that describes the relationship between power, amperage, and voltage. Watt's Law states that power, measured in watts, is equal to current, measured in amps, multiplied by voltage, measured in volts.

waveforms

The type or shape of a wave produced by alternating current. Waveforms can be measured by oscilloscopes.

wiggy

A testing device that vibrates when a current is detected. Wiggies, or solenoid voltmeters, are small and durable but can be replaced by more versatile and safer digital multimeters.

zero

To change a scale or digital reading to initially measure zero. To zero out an ohmmeter ensures it reads zero resistance before it is introduced to a circuit or component.