Slide 1: www.spacetec.org SpaceTEC® Certification
Readiness Course Basic Electricity
Slide 2: 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
Slide 4: 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..
Slide 8: 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
Slide 9: 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
Slide 11: 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
Slide 13: 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
Slide 14: www.spacetec.org Placement of electrons in a copper atom +29 Complete with 2 Complete with 8 Complete with 18 Incomplete with 1
Slide 15: www.spacetec.org Electricity-the flow of free electrons Bound electron Free electron Valance electron Negative source Positive source
Slide 16: www.spacetec.org Atomic structure of conductors,
insulators, and semiconductors Insulator - full
valence shell Conductor - 1 to 3
valence electrons Semiconductor - 4
valence electrons
Slide 17: 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
Slide 18: www.spacetec.org GENERIC CIRCUIT Electron
current
flow Control
Device Power
Source Load
Device Conductor Protective
Device
Slide 19: 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
Slide 21: www.spacetec.org CURRENT - The rate of flow of electrons Measurement
Point One Coulomb
Per Second = One Ampere = One Coulomb
Slide 22: www.spacetec.org CURRENT MEASUREMENT Connected in Series Circuit Schematic
Slide 23: www.spacetec.org VOLTMETER VOLTMETER - Connected in parallel
to measure battery
voltage. - Connected in parallel
to measure lamp voltage.
Slide 24: 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
Slide 27: 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
Slide 28: 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
Slide 29: 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)
Slide 32: www.spacetec.org SOLVING EXAMPLE 20-1 Energy = Power x Time E = (100 W) (300 s) E = 30,000 J E = 30 kJ
Slide 33: 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
Slide 34: 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
Slide 36: 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
Slide 37: www.spacetec.org STEPS IN SOLVING PROBLEM 12-4 24 V 4 Infinite
(open) 24 V 0 Infinite
Slide 38: 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
Slide 42: 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
Slide 43: www.spacetec.org EFFECT OF A SHORT CIRCUIT
ACROSS PARALLEL BRANCHES
Troubleshooting : www.spacetec.org Troubleshooting Parallel
Short: Fuse blows
Open: Less current
Slide 45: www.spacetec.org KIRCHHOFF’S VOLTAGE LAW VT = V1 + V2 +V3 VT - V1 - V2- V3 = 0 +24V - 4V - 8V - 12V = 0
Slide 46: www.spacetec.org KIRCHHOFF’S CURRENT LAW IT = I1 + I2 + I3 IIN = IOUT
Slide 47: www.spacetec.org TYPES OF DIRECT CURRENT
Slide 48: www.spacetec.org AC WAVEFORMS
Slide 49: www.spacetec.org GENERATOR PRINCIPLE Moving conductor Magnetic field Induced voltage
Slide 50: www.spacetec.org CYCLE One complete wave of alternating current or voltage
Slide 51: www.spacetec.org PERIOD The time required to produce one complete cycle
Slide 52: www.spacetec.org FREQUENCY The number of cycles produced per second Frequency = Period 1 F = T 1 = 0.25 s 1 = 4 Hz
Slide 53: www.spacetec.org PEAK VALUE The maximum voltage or current value
Slide 54: 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
Slide 55: 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 = 2fL
Slide 59: www.spacetec.org APPLYING DC VOLTAGE TO A COIL Magnetic field
builds up
Slide 60: www.spacetec.org REMOVING THE DC VOLTAGE Magnetic field
collapses
Slide 61: 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
Slide 62: www.spacetec.org EXAMPLE 30-4 XL = ? XL = 2fL = (2) (3.14) (1000 Hz) (0.2 H) = 1,256
Slide 63: 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
Slide 64: www.spacetec.org EXAMPLE 31-2 VS = 2 x 120 V = 240 V Turns ratio = = 1:2
Slide 65: www.spacetec.org EXAMPLE 31-3 Turns ratio = = = 20:1
Slide 66: www.spacetec.org EXAMPLE 31-4 60 V
25 = 2.4 A IP = 5 x IS
= 5 x 2.4 A
= 12 A IS = =
Slide 67: www.spacetec.org DIODE CHARACTERISTIC CURVE Avalanche
current
Slide 68: www.spacetec.org DIODE LEAD IDENTIFICATION
Slide 69: www.spacetec.org BRIDGE RECTIFIER
Circuit Protection : www.spacetec.org Circuit Protection Fuses
Circuit breakers
Overload
Thermal shunt
Slide 71: www.spacetec.org OVERLOADED CIRCUIT Branch circuit
rating:
15 A / 120 V
1500 W Total power = 2640 W Total current = 22 A
Slide 72: www.spacetec.org FUSES
Slide 73: www.spacetec.org CIRCUIT BREAKERS
Slide 74: www.spacetec.org CURRENT
RATINGS
Slide 75: www.spacetec.org USING AN OHMMETER TO
TEST FUSES
Slide 76: www.spacetec.org THERMAL OVERLOAD
PROTECTION Fuse protects
wiring
Slide 77: www.spacetec.org AUTO STARTER MOTOR CIRCUIT Starter
motor Battery High-current
wiring Low-current
wiring Electromagnetic Switch
or
Solenoid
Or
Starter Relay
Slide 78: www.spacetec.org TRANSISTOR CONTROLLED RELAY 20 mA
of control
current controls
10 A of
load
current Electromagnetic
Slide 79: 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
Slide 81: www.spacetec.org HIGH-RESISTANCE CONNECTIONS Loose Connection Corroded Connection
Slide 82: www.spacetec.org CONNECTING TO
TERMINAL SCREWS Bend wire
into a loop Hook wire
over the screw
Slide 83: 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
Slide 89: 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
Slide 90: 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
Slide 92: 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
Slide 94: 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
Slide 95: 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
Slide 98: www.spacetec.org This Concludes The Basic Electronics Readiness Review
GOOD LUCK !!