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Electrical Quantities, Circuits,, Test Instruments, and Safety : Electrical Quantities, Circuits,, Test Instruments, and Safety Objectives 319.1 Evaluate the characteristics and Components of various electrical circuits.

Electrical Quantities, Circuits,, Test Instruments, and Safety : Electrical Quantities, Circuits,, Test Instruments, and Safety Objectives 319.2 Identify various electrical test equipment and describe their uses. Read and correctly identify the information provided on a digital or analog meter display.

Electrical Quantities, Circuits,, Test Instruments, and Safety : Electrical Quantities, Circuits,, Test Instruments, and Safety Objectives 319.3 Recognize the hazards associated with electrical circuits. Mitigate these hazards using safe work habits, proper protection equipment, and proper procedures.

Questions to be answeredduring lesson : Questions to be answeredduring lesson 1. Water held behind a dam has ____ energy based on its retained position. 2. _____ power generating plants produce most of the electricity used in the united states. 3. In the United States , the major portion of the electric power produced is used for _____. 4. _____ power is measured in VAR and is the power delivered to inductive and capacitive loads in an electrical circuit. 5. A compressed spring, such as used in an electromagnetic relay, has _____ energy because of its physical condition. 6. When additional 120-volt loads are correctly connected to a 120-volt circuit, the total circuit impedance ____.

Questions to be answeredDuring Lesson : Questions to be answeredDuring Lesson The measurements made with multimeters can be indicated in ____ form. Protective clothing includes clothes that are ____ resistance. Although possible in systems of lesser voltage, the possibility of an arc blast occurance is greatest from electrical systems operating at or above ____ volts. NFPA 70E states that only qualified persons shall perform testing work on or near live parts operating at ____ volts or more.

Energy : Energy Energy is the capacity to do work. The two forms of energy are: Potential energy kinetic energy

Potential Energy : Potential Energy Stored energy a body has due to its position, chemical state, or condition. Examples: Water behind a dam A battery Compressed spring

Kinetic Energy : Kinetic Energy Energy of Motion. Examples: Falling water; Energy released when water runs trough the dam. The starting of a motor connected to a battery is used to produce a rotating mechanical force on a motor shaft

Energy Sources used to Produce Electricity : Energy Sources used to Produce Electricity Coal Nuclear Power Natural gas Oil Wind Solar Power Water

Energy Sources used to Produce Electricity : Energy Sources used to Produce Electricity These energy sources are used to produce work when converted to electricity, steam, heat, and mechanical force. Some energy sources, such as coal, oil, and natural gas, are consumed in use. Energy sources such as wind, solar power, and water are not consumed in use.

Energy Sources : Energy Sources Production of electricity Coal produces 50% Nuclear power 20% Natural Gas 18% Oil 3% Solar power & Water 9%

Electricity : Electricity Approximately 62% of all electricity is converted into rotary motion by motors. Three phase motors uses the largest amount of electricity in commercial and industrial applications. They are used because of they are the most energy-efficient motors.

Electricity : Electricity Approximately 20% of all electricity is converted into light by lamps. The most common lamps used: Residential incandescent lamps. Commercial and industrial fluorescent lamps. Warehouse and factory High-intensity discharge HID.

Electricity : Electricity Approximately 18% of all electricity is used to produce; Heat Linear motion Audible signals Visual outputs

Questions : Questions Water held behind a dam has ____ energy based on its retained position. (a) potential (b) released (c) kinetic (d) radiant ____ power generating plants produce most of the electricity used in the United States. (a) Nuclear (b) Coal-fired (c) Hydroelectric (d) Natural-Gas-fired In the united States, the major portion of the electric power produced is used for ____. (a) lighting (b) heating (c) cooling (d) motors

Production of Electricity : Production of Electricity To produce electricity you must convert potential energy directly or indirectly into electricity. The majority of all electricity is produced indirectly by converting potential energy into electricity using a generator. A generator produces electricity when magnetic lines of force are cut by a rotating wire coil (rotor). As the rotor rotates through the magnetic field, electric current flow is produced through the wire coils of the rotor.

Production of Electricity : Production of Electricity Electric current from the wire coil is conducted to the load through slip rings. The voltage produced by generator depends on the strength of the magnetic field and the rotational speed of the rotor. The stronger the magnetic lines of force and the faster the rotational speed, the higher the voltage produced.

Production of Electricity : Production of Electricity In larger generator applications, the generator output is connected to transformers A Transformer is an electric device that uses electromagnetism to change voltage from one level to another or to isolate one voltage from another. Transformers normally step up voltage so power can be transmitted at a lower current level.

Production of Electricity : Production of Electricity AC generators that has one rotating coil produces a single-phase output. Single-phase generators are used for small power demands, but are not practical or economical for producing large amounts of power. To produce larger amounts of power, three single-phase coils are coupled to produce three-phase power. The three coils are spaced 120 electrical degree apart. The AC voltage outputs are phase 1(A), phase 2 (B), and phase 3(C).

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Electrical Abbreviations/Prefixes : Electrical Abbreviations/Prefixes

Voltage : Voltage The amount of electrical pressure in a circuit is called voltage. Voltage is also known as electromotive force (EMF) or potential difference. Voltage is produced when electrons are freed from atoms. Voltage is either direct (DC) or alternating (AC). DC voltage is voltage that flows in one direction only. AC voltage is voltage that reverses its direction of flow at regular intervals.

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DC Voltage : DC Voltage All DC voltage sources have a positive and a negative terminal. Positive and negative terminals establish polarity in a circuit. Polarity is the positive (+) or negative(-) state of an object. All points in a DC circuit have polarity. Batteries and photovoltaic cells produce the most common DC voltage.

DC Voltage : DC Voltage Another source to produce DC voltage is rectified AC voltage. A rectifier is a device that converts AC voltage to DC voltage by allowing the voltage and current to flow in only one direction. Current DC voltage levels include; 1.5V, 6V, 9V, 12V, 24V, 36V, and 125V. You must take caution when measuring DC voltages over 60V.

DC Voltage : DC Voltage When taking DC voltages measurements with a digital multimeter (DMM) the following procedures should be taken. Set the function switch to DC voltage. Set the meter to its highest possible circuit voltage. Plug the black test lead into the common jack. Plug the red test lead into the voltage jack. Discharge any capacitors. Connect the black test lead to circuit ground and the red test lead to the point at which the voltage is under test. Reverse the black and red test leads if a negative sign apperas in front of the reading on the DMM. Read the voltage display.

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AC Voltage : AC Voltage AC voltage is the most common voltage used to produce work. AC voltage is produced by generators, which create AC sine waves as they rotate. An AC sine wave is a symmetrical waveform that contains 360 electrical degrees. The wave reaches its peak positive value at 90 deg, returns to 0 v at 180 deg, increases to its peak negative value at 270 deg, and returns to 0 deg at 360 deg.

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AC Voltage. : AC Voltage. Cycle: Is one complete positive and negative altenation of a wave form. An alternation is half of a cycle. A sine wave has one positive alternation and one negative alternation. Ac voltage is either single phase or three phase. Single phase only has one alternating sine wave form and three phase has a combination of three alternating voltage waveforms, each displaced 120 electrical degrees apart.

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Current : Current Is the amount of electrons flowing through an electrical circuit. An ampere is the number of electrons passing a given point in one second. Current can be direct current or alternating current. DC current flows in only one direction. Direct current flows in any circuit connected to a power supply producing a DC voltage. AC current is current that reverses its direction of flow at regular intervals. Alternating current flows in any circuit connected to a power supply producing an AC voltage.

Current Flow : Current Flow Early scientists believed electrons flowed from positive to negative. When atomic structure was studied, electron flow from negative to positive was introduced. Conventional current flow is current flow from positive to negative. Electron current flow is current flow from negative to positive. Both current theories are still used.

Current MeasurementProcedures : Current MeasurementProcedures Taken AC or DC Current Measurements. Follow recommended procedures when testing DMM fuses. Start with the highest current-measuring range if the load current is unknown. If you think the current measurements may exceed the limit of the of the DMM setting, use a clamp-on ammeter or do not take the measurement. Make sure the meter function switch is set to the proper setting for measuring current AC or DC. Make sure the leads are connected to the proper jacks for measuring current.

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Resistance : Resistance Resistance is the opposition to the flow of electrons. Resistance is measured in ohms. Resistance limits the flow of current in an electrical circuit. The higher the resistance the lower the current flow and likewise the lower the resistance the higher the current flow. Material like rubber and plastic have high resistance, where copper and aluminum have a lower resistance. Where copper conductors of larger size and short distance will have less resistance. The same for conductors of smaller sizes and longer distance will have more resistance.

Resistance Measurements : Resistance Measurements Insure that all power is removed from the equipment before taken resistance measurements. Remove component if possible. Set switch on your meter to the resistance position. Plug the black test lead into the common jack. Plug the red test lead into the resistance jack. Check the battery. The battery symbol is displayed when the battery is low. Ensure that contact between the test leads are good. Do not hold the leads against the test opject with your fingers on the leads.

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Ohm’s Law : Ohm’s Law Ohm’s law is the relationship between voltage, current, and resistance in a circuit. Any value in this relationship can be found if any two are known. E = I x R I = E/R R = E/I

Series Circuit : Series Circuit A series connection is a connection that has two or more components connected so there is only one path for current flow. In a series circuit: The voltage in a circuit will add up. The resistance in a circuit will add up. The current in a circuit will remain the same through- out the circuit Et = E1 + E2 + E3 … Rt = R1 + R2 + R3 … It = I1 = I2 = I3 …

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Parallel Circuits : Parallel Circuits A parallel connections is a connection that has two or more components connected so there is more than one path for current flow. In a parallel circuit: Voltage will remain the same. Resistance will add up. Current will add up. Et = E1 = E2 = E3 Rt = R1 x R2 R1 + R2 It = I1 + I2 + I3

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Series-Parallel Circuits : Series-Parallel Circuits A series/parallel connection is a combination of series- and parallel connected components. The total resistance in a circuit containing series/parallel connected resistors equals the sum of the series loads and the equivalent resistance of the parallel combinations. The total current and current in individual parts of a series/parallel circuit follow the same laws of current as in a basic series and a basic parallel circuit The total voltage applied across resistors (loads) connected in a series/parallel combination is divided across the individual resistors (loads).

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Power Formula : Power Formula Power is the rate of doing work or using energy. The power formula is the relationship between power, voltage, and current in an electrical circuit. P = E x I E = P/I I = P/E

Power : Power Power is the rate of doing work or using energy. True power is the actual power used in an electrical circuit. True power is the power that is converted into work for use by devices, such as sound produced by speakers, rotary motion produced by motors, light produced by lamps, linear motion produced by solenoids, and heat produced by heating elements. True power is measured in watts. kilowatts, or megawatts.

Reactive Power : Reactive Power Is power supplied to a reactive load. The unit of reactive power is voltamps reactive (VAR). True power represents a pure resistive component or load and VAR represents a pure reactive (capacitor or coil) component or load. In an AC circuit in which voltage and current are in phase, such as a circuit containing only resistance, the power in the circuit is true power. Almost all AC circuits include circuits include capacitive reactance (from capacitors) and/or inductive reactance (from coils), inductive reactance is the most common, because all motors, transformers, solenoids, and coils have inductive reactance.

Apparent Power : Apparent Power Is the product of the voltage and current in a circuit calculated without considering the phase shift that may be present between the voltage and the current in a circuit. True Power represents a pure resistance component or load in which voltage and current are in phase. Reactive power represents a pure inductive load or capacitor load in which voltage and current are out of phase. Apparent power represents a load or circuit that includes both true power and reactive power.

Phase Shift : Phase Shift Is the state in which voltage and current in an AC circuit do not reach their maximum amplitude and zero level simultaneously. In-Phase is the state in which voltage and current in an AC circuit reach their maximum amplitude and zero level simultaneously. Some electrical circuits include only one load type, such as a heating element. However, most electrical circuits include several different load types, such as motors, solenoids, and lamps in addition to heating elements. Each load affects the electrical system in a different way. Some loads cause a phase shift in the circuit.

Resistive Circuits : Resistive Circuits A circuit that contains only resistance, such as heating elements and incandescent lamps. All electrical circuits include some resistance because all conductors, switch contacts, connections, and/or loads have resistance. AC voltage and current are in-phase in resistive circuits.

Inductive Circuits : Inductive Circuits Inductance is the property of a circuit that causes it to oppose a change in current due to energy stored in a magnetic field. Inductance is normally stated in henrys, millihenrys, or microhenrys. When current flows through a conductor, a magnetic field is produced around the conductor. A conductor formed into a coil produces a strong magnetic field when current flows through the coil. AC current flow produces an alternating magnetic field around the coil. DC current flow produces a constant magnetic field around the coil.

Inductive Circuits : Inductive Circuits In an AC circuit, the magnetic field is continuously building and collapsing until the circuit is opened. The magnetic field also changes direction with each change in sine wave alternation. In a DC circuit, a magnetic field is created and remains at maximum potential until the circuit is opened. Once the circuit is opened, the magnetic field collapses. Coils commonly found in motor windings, transformers, and solenoids create inductance in an electrical circuit. A phase shift occurs between alternating voltage and current in an inductive circuit.

Inductive Circuits : Inductive Circuits An inductive circuit is a circuit in which current lags voltage. The greater the inductance in a circuit, the larger the phase shift. Inductive Reactance is the opposition of an indicator to alternating current. Inductive reactance is measured in ohms just like resistance. The amount of inductive reactance in a circuit depends on the amount of inductance (in henrys) of the coil (inductor) and the frequency of the current. Inductance is normally a fixed amount. Frequency may be fixed or variable amount.

Capacitive Circuits : Capacitive Circuits Capacitance is the ability of a component or circuit to store energy in the form of an electrical charge. A capacitor is an electrical device that stores electrical energy by means of an electrostatic field. The unit of capacitance is the Farad. Capacitors create capacitance in an electrical circuit. A phase shift occurs between voltage and current in a capacitive circuit. A Capacitive circuit is a circuit in which current leads voltage (voltage lags current) Capacitive Reactance is the opposition to current flow by a capacitor.

Power Factor : Power Factor Is the ratio of true power used in a AC circuit to apparent power delivered to the circuit. True power equals apparent power only when the power factor is 100%. When the power is less than 100%, the current is less efficient and has a high operating cost because not all current is performing work. To calculate power factor, apply the formula: PF = True power x 100 Apparent power

Ohm’s Law and Impedance : Ohm’s Law and Impedance Ohm’s law is limited to circuits in which electrical resistance is the only significant opposition to the flow of current. In DC circuits and AC circuits that do not contain a significant amount of inductance and/or capacitance, the opposition to the flow of current is resistance (R). In circuits that contain inductance or capacitance, the opposition to the flow of current is reactance. In circuits that contain resistance and reactance, the combined opposition to the flow of current is impedance (Z). Impedance is stated in ohms.

Ohms Law and Impedance : Ohms Law and Impedance Ohm’s law is used in circuits that contain impedance; however, Z is substituted for R in the formula. Z represents the total resistive force (resistance and reactance) opposing current flow. E = I x Z I = E/Z Z = E/I

Questions : Questions ____ Power is measured in VAR and is the power delivered to inductive and capacitive loads in an electrical circuit. (a) True (b) Apparent (C) Reactive A compressed spring, such as used in an electromagnetic relay, has ____ energy because of its physical condition. (a) kinetic (b) potential (c) radiant (d) released When additional 120-volt loads are correctly connected to a 120-volt circuit, the total circuit impedance ____. (a) decreases (b) increases

Electrical Tools and Test Instruments319.2 : Electrical Tools and Test Instruments319.2