BasicElectricity

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www.spacetec.org SpaceTEC® Certification Readiness Course Basic Electricity

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www.spacetec.org Never touch a downed wire Don’t bring appliances near water Stay clear of power lines NO power tools on wet grass or wet surfaces Ground Fault Circuit Interruptors on ALL outdoor electrical outlets (GFCI)

GFCI Block Diagram : 

www.spacetec.org GFCI Block Diagram Circuit Breaker GFCI Wall Plug Trip Requirements: 10 millisecond response time 5 milliamp difference in outgoing and returning current

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www.spacetec.org Wear appropriate attire Hard hat Goggles Tight clothing No rings Or metal jewelry Safety shoes Lockout Tagout Wear earmuffs in noisy areas Confine long hair or keep It trimmed when working Around machinery Breathing Protection

Body Resistance and Shock : 

www.spacetec.org Body Resistance and Shock Electrical resistance is defined as the opposition to flow of current in a circuit Resistance is measured in OHMS The lower the body resistance, the greater the potential shock hazard Body resistance can be measured with an ohm meter Any current flow above 5 milli-amperes is considered dangerous

Skin Conditions and Resistance : 

www.spacetec.org Skin Conditions and Resistance Dry skin resistance: 100,000 to 600,000 Ohms Wet skin resistance: 1,000 Ohms Internal body….hand to foot: 400 to 600 Ohms Ear to ear: about 100 Ohms Burns and neurological damage are the most common injuries caused by electrical shock THE DANGER OF HARMFUL SHOCK INCREASES AS THE VOLTAGE INCREASE VOLTAGES AS LOW AS 30V Can Be Dangerous !!

First Aid For Electrical Shock : 

www.spacetec.org First Aid For Electrical Shock Turn power OFF & remove victim from electric contact. Do Not touch victim until power is removed. Apply artificial respiration if not breathing. Keep victim warm. Keep victim head low so blood can flow to brain. Avoid placing victim where breathing obstruction may occur. Cold water or ice pack for first degree and minor second degree. Don’t break blisters ! For open blisters…no water or cold packs…use thick clean bandages to avoid infection. Do not remove charred clothing ..let a medical pro do it..

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www.spacetec.org The Powers of Ten and Scientific Notation. It is often used in electronics to express very large numbers and very small numbers. Very small numbers are expressed by using negative powers of ten. For example, 3.2 x 10-8 is a scientific notation for the number 0.000000032. Here, “ten to the minus eight power” means “move the decimal place in 3.2 eight places to the left.” 4 7.9 x 10 = 79,000 9.1 x 10 8 = 910,000,000 7.9 x 10 -4 = 0.00079 Metric and Prefix Notations

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www.spacetec.org Note: Symbols in red are most used……know them Metric and Prefix Notations

Prefix Examples : 

www.spacetec.org Prefix Examples 0.002A = 2 X 10-3A = 2mA 100kV = 100 X 10+3V = 1 x 10+5V= 100,000V 100µs = 100 x 10-6s = 1 x 10-4s = 0.0001s

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www.spacetec.org Structure of an atom Neutron (No Charge) Proton (Positive Charge) Electron (Negative Charge) Shell or energy level Most of the mass of an atom is located in its nucleus

Electron Configuration : 

www.spacetec.org Electron Configuration The Electron Configuration is the orbital description of the locations of the electrons in an unexcited atom Electrons orbit in “SHELLS” or “Energy Levels” The higher the orbit, the higher the “Energy Level” Atoms react based on the Electron Configuration The outermost electron shell is the most important as far as conductivity properties are concerned

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www.spacetec.org 13 P 14 N Bohr model of the aluminum atom 13=13 Protons = Electrons Net charge is neutral or zero Electrically Neutral

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www.spacetec.org Placement of electrons in a copper atom +29 Complete with 2 Complete with 8 Complete with 18 Incomplete with 1

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www.spacetec.org Electricity-the flow of free electrons Bound electron Free electron Valance electron Negative source Positive source

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www.spacetec.org Atomic structure of conductors, insulators, and semiconductors Insulator - full valence shell Conductor - 1 to 3 valence electrons Semiconductor - 4 valence electrons

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www.spacetec.org Multimeter voltage current resistance Voltage tester voltage level rugged construction Clip-on ammeter measures current without direct connection Digital circuit probe measures digital logic levels Oscilloscope used to measure and examine voltage waveforms Instruments

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www.spacetec.org GENERIC CIRCUIT Electron current flow Control Device Power Source Load Device Conductor Protective Device

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www.spacetec.org VOLTAGE - The difference in electric charge between two points. 1 Volt - Difference in Electric Charge Produces 1 Ampere of Current Flow.

VOLTAGE = Electromotive Force : 

www.spacetec.org VOLTAGE = Electromotive Force Voltage, also called electromotive force, is a quantitative expression of the potential difference in charge between two points in an electrical field. For electrons to flow, there must be a source of electromotive force (emf), or voltage Electromotive force can be produced by a variety of different primary energy sources

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www.spacetec.org CURRENT - The rate of flow of electrons Measurement Point One Coulomb Per Second = One Ampere = One Coulomb

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www.spacetec.org CURRENT MEASUREMENT Connected in Series Circuit Schematic

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www.spacetec.org VOLTMETER VOLTMETER - Connected in parallel to measure battery voltage. - Connected in parallel to measure lamp voltage.

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www.spacetec.org RESISTANCE MEASUREMENT Measured with an Ohmmeter (multimeter used as an ohmmeter) Ohmmeters should never be connected to live circuits!

Meter Safety : 

www.spacetec.org Meter Safety Never use an ohmmeter on a live circuit Never connect an ammeter in parallel with a voltage source Use proper range settings: Do NOT overload a meter Do not short terminals using meter probes Never measure unknown high voltages: find out the range before attaching a meter Check for frayed or broken meter leads Avoid touching exposed meter probes If possible, connect meter before applying power to circuit When connecting a meter to a live circuit work with one hand at your side to lessen the danger of shock To reduce the danger of accidental shock, disconnect meter test leads immediately after completing a measurement

Resistors Oppose & Control The Flow of Current in a Circuit : 

www.spacetec.org Resistors Oppose & Control The Flow of Current in a Circuit Series Parallel Units: Ohm Symbol R1, R2, etc schematic representation Series Parallel Symbol IT I1 I2 I3 I4

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www.spacetec.org OHM’S LAW FORMULAS Current equals voltage divided by resistance Voltage equals current multiplied by resistance Resistance equals voltage divided by current Find Current Find Voltage Find Resistance

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www.spacetec.org VOLTAGE - CURRENT - RESISTANCE Quantity Unit of Measure Function Name Name Symbol Symbol Voltage V, emf or E Voltage V Pressure which makes current flow Current I Ampere A Rate of flow of electrons Resistance R Ohm  Opposition to current flow

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www.spacetec.org POWER -The amount of electric energy converted to another form in a given length of time. Power = Voltage x Current Watts = Volts x Amperes P = V x I

Cable Power LossP = I 2 x R : 

www.spacetec.org Cable Power LossP = I 2 x R P = V x I = (I x R) x I = I2 x R Recall: V = I x R Power loss in cable: P = I2 x RWire P = power in watts (W) I = current in amperes (A) R = resistance in Ohms (Ω)

ENERGY IS THE ABILITY TO DO WORK : 

www.spacetec.org ENERGY IS THE ABILITY TO DO WORK Energy is measured in Joules or kWh Energy is stored in a battery or a gallon of gasoline ……..Or stored in water behind a dam ……..Or stored in a body in motion Energy can be converted from one form to another We pay for electricity based on energy used: example $0.10 per kWh We buy gasoline by the gallon(126MJ/gallon) Power is the RATE at which Energy is transferred or consumed Power is measured in Watts or Horsepower 1 Watt = 1 Joule/second 1Joule = (1Watt) x (1second)

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www.spacetec.org SOLVING EXAMPLE 20-1 Energy = Power x Time E = (100 W) (300 s) E = 30,000 J E = 30 kJ

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www.spacetec.org ENERGY - Electric energy refers to the energy of moving electrons Energy = Power x Time kWh = kilowatts x hours Measured with a kilowatthour energy meter

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www.spacetec.org SOLVING EXAMPLE 20-6 Rated for 4.2 kW Used 20 h/month Cost of 12¢ per kWh Energy = Power x Time = (4.2 kW) x (20 h) = 84 kWh Cost = Energy x rate per kWh = (84 kWh) x ($0.12) = $10.08

Series Circuit : 

www.spacetec.org Series Circuit Same current through each component Sum of voltage drops = supply voltage (Kirchoff Voltage Law) Largest resistance has the largest voltage drop. Add resistance Lowers current One open the circuit fails. The total resistance is the sum of all resistors: RT = R1 + R2 + R3 I IT

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www.spacetec.org STEPS IN SOLVING PROBLEM 12-2 20 k 3 mA 12 V 6 V 42 V 180 mW 36 mW 18 mW 126 mW

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www.spacetec.org STEPS IN SOLVING PROBLEM 12-4 24 V 4  Infinite (open) 24 V 0 Infinite

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www.spacetec.org STEPS IN SOLVING PROBLEM 12-5 60 V 4 k 2 k 0 (Short) 6 k 10 mA 40 V 20 V 0 600 mW 200 mW 400 mW 0 mW

Troubleshooting : 

www.spacetec.org Troubleshooting Series Circuit Open: No current Source voltage at the open Rest are zeros Short Current Increase V is zero at the short

Parallel Circuit : 

www.spacetec.org Parallel Circuit Same Voltage across all components Smallest resistance, most current. Add a branch: Increase Current Decrease Overall Resistance One branch opens, current is smaller than normal. Resistance of Network is less than smallest resistor

Parallel Resistor Network : 

www.spacetec.org Parallel Resistor Network From Kirchoff’s Current Law: IT = I1 + I2 + I3 + ------ + IN From Ohm’s Law: I = V/R and R = V/I IT = VT R1 + VT R2 + VT R3 + ---- + VT RN = 1 R1 + 1 R2 + 1 R3 + ---- + RN 1 VT RT = VT / IT = 1 R1 + 1 R2 + 1 R3 + ---- + RN 1 1

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www.spacetec.org STEPS IN SOLVING PROBLEM 13-3 1.5 A 1 A 3 A 8  4.36  132 W 72 W 36 W 24 W

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www.spacetec.org EFFECT OF A SHORT CIRCUIT ACROSS PARALLEL BRANCHES

Troubleshooting : 

www.spacetec.org Troubleshooting Parallel Short: Fuse blows Open: Less current

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www.spacetec.org KIRCHHOFF’S VOLTAGE LAW VT = V1 + V2 +V3 VT - V1 - V2- V3 = 0 +24V - 4V - 8V - 12V = 0

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www.spacetec.org KIRCHHOFF’S CURRENT LAW IT = I1 + I2 + I3 IIN = IOUT

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www.spacetec.org TYPES OF DIRECT CURRENT

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www.spacetec.org AC WAVEFORMS

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www.spacetec.org GENERATOR PRINCIPLE Moving conductor Magnetic field Induced voltage

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www.spacetec.org CYCLE One complete wave of alternating current or voltage

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www.spacetec.org PERIOD The time required to produce one complete cycle

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www.spacetec.org FREQUENCY The number of cycles produced per second Frequency = Period 1 F = T 1 = 0.25 s 1 = 4 Hz

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www.spacetec.org PEAK VALUE The maximum voltage or current value

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www.spacetec.org SOLVING EXAMPLE 21-1 ?? I rms = I peak x 0.707 I rms = (10 A) x (0.707) I rms = 7.07 A

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www.spacetec.org SOLVING EXAMPLE 21-2 Vpeak = Vrms x 1.414 Vpeak = (120 V) (1.414) Vpeak = 170 V Vp-p = Vpeak x 2 Vp-p = (170 V) x (2) Vp-p = 340 V

Common Circuit Symbols : 

www.spacetec.org www.spacetec.org Full Wave Rectifier Operational Amplifier Opto Coupler Transformer Iron Core Light- Emitting Diode(LED) Electrolytic Capacitor Potentiometer Normally Open Pushbutton Switch Normally Closed Pushbutton Switch Transformer Air Gap NPN Transistor PNP Transistor Darlington PNP Transistor Alternating Current Source Relay Current Controlled Switch Zener Diode Voltage Controlled Switch Diode Battery Fuse Triode Quartz Crystal Resistor Variable Inductor Inductor Variable Capacitor Ground Lamp Common Circuit Symbols Single Pole Single Throw Normally Open

Common AC Circuit Components : 

www.spacetec.org Common AC Circuit Components Resistors Capacitors Inductors Transformers AC Power Source R, Resistance in Ohms C, Capacitance in Farads L, Inductance in Henry’s

Ohm’s Law : 

www.spacetec.org Ohm’s Law Capacitive Reactance = XC = VC = I • XC VL = I • XL VR = I • R Inductive Reactance = XL = 2fL

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www.spacetec.org APPLYING DC VOLTAGE TO A COIL Magnetic field builds up

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www.spacetec.org REMOVING THE DC VOLTAGE Magnetic field collapses

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www.spacetec.org MUTUAL INDUCTANCE Changing magnetic field created Φ = MMF/R MMF = Magneto Motive Force In Amp-Turns R = Reluctance Φ = Flux V = N d Φ dt

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www.spacetec.org EXAMPLE 30-4 XL = ? XL = 2fL = (2) (3.14) (1000 Hz) (0.2 H) = 1,256 

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www.spacetec.org IDEAL TRANSFORMER Power in = Power out V x I primary = V x I secondary (120 V) (0.625 A) = (15 V) x (5 A) 75 VA = 75 VA The basis for transformer operation is mutual inductance

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www.spacetec.org EXAMPLE 31-2 VS = 2 x 120 V = 240 V Turns ratio = = 1:2

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www.spacetec.org EXAMPLE 31-3 Turns ratio = = = 20:1

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www.spacetec.org EXAMPLE 31-4 60 V 25  = 2.4 A IP = 5 x IS = 5 x 2.4 A = 12 A IS = =

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www.spacetec.org DIODE CHARACTERISTIC CURVE Avalanche current

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www.spacetec.org DIODE LEAD IDENTIFICATION

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www.spacetec.org BRIDGE RECTIFIER

Circuit Protection : 

www.spacetec.org Circuit Protection Fuses Circuit breakers Overload Thermal shunt

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www.spacetec.org OVERLOADED CIRCUIT Branch circuit rating: 15 A / 120 V 1500 W Total power = 2640 W Total current = 22 A

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www.spacetec.org FUSES

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www.spacetec.org CIRCUIT BREAKERS

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www.spacetec.org CURRENT RATINGS

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www.spacetec.org USING AN OHMMETER TO TEST FUSES

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www.spacetec.org THERMAL OVERLOAD PROTECTION Fuse protects wiring

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www.spacetec.org AUTO STARTER MOTOR CIRCUIT Starter motor Battery High-current wiring Low-current wiring Electromagnetic Switch or Solenoid Or Starter Relay

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www.spacetec.org TRANSISTOR CONTROLLED RELAY 20 mA of control current controls 10 A of load current Electromagnetic

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www.spacetec.org RELAY CONTACTS Single-pole, double-throw (SPDT) Double-pole, single-throw (DPST) Double-pole, double-throw (DPDT)

Connections : 

www.spacetec.org Connections High Resistance Connections Strip Crimp Solder (tin lead, 63/37) Screw terminal Type Heat shrink Cable splicing and bending

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www.spacetec.org HIGH-RESISTANCE CONNECTIONS Loose Connection Corroded Connection

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www.spacetec.org CONNECTING TO TERMINAL SCREWS Bend wire into a loop Hook wire over the screw

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www.spacetec.org CRIMP-ON CONNECTOR Flattened Turned in Compressed The Crimp-on is also called aCompressionConnector

Crimp-Terminal Lugs : 

www.spacetec.org Crimp-Terminal Lugs Remember: The size of the connector Must be matched to the Wire gauge size

Splicing Wires : 

www.spacetec.org Splicing Wires

Solder : 

www.spacetec.org Solder Solder is an alloy of tin and lead Lead/tin ratio determines strength and melting point Wire type 60/40 tin/lead is recommended for most electrical/electronic work Item being soldered must be cleaned of dirt and oxide…..otherwise solder will not adhere to the splice

Solder Flux : 

www.spacetec.org Solder Flux Soldering flux prevents oxidation of the copper surfaces by insulating the surface from air Acid and resin based solders are available Acid based solder SHOULD NOT be used for electrical work as it corrodes copper wire Resin flux is available in paste form or as a continuous core inside solder wire and should be used in electrical work

Misalign Splices in a Cable : 

www.spacetec.org Misalign Splices in a Cable Splices should be distributed in a cable to avoid a large bulge in the cable splice splice splice splice splice

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www.spacetec.org SOLDERING TO A TERMINAL Make a loop around the terminal Bend the wire through and around the terminal hole Apply heat Apply solder

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www.spacetec.org CONDUCTOR FORMS

Maintain Minimum Cable Bends : 

www.spacetec.org Maintain Minimum Cable Bends A cable bend radius of at least 10 times the diameter should be maintained True for wire and fiber cable Fiber cable can suffer increased attenuation from too sharp a bend

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www.spacetec.org AWG WIRE SIZES The larger the gauge number the smaller the actual diameter of the conductor. The primary cable selection criteria are current rating and allowable voltage drop

Static Electricity : 

www.spacetec.org Static Electricity STATIC: Having no motion; at rest STATIC ELECTRICITY: Electrical charge at rest. FYI Electrical charges are caused by an imbalance of electrons on the surface atoms of materials. Primarily due to triboelectric charging between materials where electrons from surface atoms are transferred between materials creating an electrostatic potential. Electrostatic field surrounds electrostatically charged objects. ESD: A hare raising experience

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www.spacetec.org Producing Static Electricity by Friction Fur and rubber rod rubbed together Charge accumulates at end of rod only Electrons move from the fur to the rod Negative charge produced on the rod

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www.spacetec.org Law of Electric Charges (Law of Electrostatics) Like charges repel Unlike charges attract

Electrostatic Discharge(ESD) : 

www.spacetec.org Electrostatic Discharge(ESD) DEFINITION: A transfer of electrostatic charge between bodies at different electrostatic potentials caused by direct contact or induced by an electrostatic field. Lightning: a mega ESD event Lightning strikes somewhere on Earth about 100 times each second!

Electrostatic Protection : 

www.spacetec.org Electrostatic Protection Electronic parts can be easily destroyed by electrostatic discharge Wearing a wrist strap tied to the local ground is the most important thing you can do to control electrostatic discharge (ESD) Wrist straps need to be checked once a week A static meter can be used to detect and measure electrostatic charge Follow the ESD procedures used by your employer

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www.spacetec.org This Concludes The Basic Electronics Readiness Review GOOD LUCK !!