NCCER Elc L1/M4 MIX

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NCCER Elc L1/M4 MIX

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  1. Objectives

    Slide 2 - Objectives

    • When trainees have completed this lesson, they should be able to do the following:
    • 1. Explain the basic characteristics of combination circuits.
    • 2. Calculate, using Kirchhoff’s voltage law, the voltage drop in series, parallel, and series-parallel circuits.
    • 3. Calculate, using Kirchhoff’s current law, the total current in parallel and series-parallel circuits.
    • 4. Using Ohm’s law, find the unknown parameters in series, parallel, and series-parallel circuits.  
    • This is a knowledge-based module; there are no Performance Tasks.
    • Electrical Theory 26104-14
  2. 1.0.0 – 2.1.0

    Slide 3 - 1.0.0 – 2.1.0

    • Electrical Theory 26104-14
    • Introduction; Resistive Circuits
    • • A series circuit contains only one path for current flow.
    • • In a series circuit, the current is equal at each point in the circuit.
  3. 1.0.0 – 2.1.0

    Slide 4 - 1.0.0 – 2.1.0

    • Electrical Theory 26104-14
    • Total Resistance
    • • In a series circuit, the total resistance is equal to the sum of the individual resistances.
    • • In the circuits shown here, the total resistance is:
    • Circuit A, 50Ω + 75Ω + 100Ω = 225Ω
    • Circuit B, 20Ω + 40Ω + 60Ω = 120Ω
  4. 2.2.0 – 2.1.0

    Slide 5 - 2.2.0 – 2.1.0

    • Electrical Theory 26104-14
    • Resistances in Parallel
    • • In a parallel circuit, the resistance is calculated by dividing the sum of the inverse values of the individual resistances by one:
    • • In the circuit shown, the total resistance is :
  5. 2.2.1

    Slide 6 - 2.2.1

    • Electrical Theory 26104-14
    • Simplified Formulas
    • • The total resistance of equal resistors in parallel is found by dividing the resistance of each resistor by the number of resistors (RT = R/N).
    • • The total resistance of two unequal resistors in parallel is found by multiplying the values of the two resistors and then dividing the sum of the two resistances:
  6. 2.3.0

    Slide 7 - 2.3.0

    • Electrical Theory 26104-14
    • Series-Parallel Circuits
    • • If a circuit does not divide, it is a series circuit.
    • • If a circuit divides into separate branches, it is a parallel circuit.
    • • If a circuit divides into separate branches and there are also series loads, it is a series-parallel circuit.
  7. 2.3.0

    Slide 8 - 2.3.0

    • Electrical Theory 26104-14
    • Redrawing a Series-Parallel Circuit
    • Series-parallel circuits can be redrawn to separate the series and parallel components.
  8. 2.3.0

    Slide 9 - 2.3.0

    • Electrical Theory 26104-14
    • Reducing Series-Parallel Circuits
    • To calculate the total resistance in a series-parallel circuit, first calculate the effective resistance of the parallel component, then add it to the resistance of the series loads.
    • Next Session…
    • Applying Ohm’s Law
  9. 2.4.0 – 2.4.1

    Slide 10 - 2.4.0 – 2.4.1

    • Electrical Theory 26104-14
    • Applying Ohm’s Law
    • • To find the voltage across individual resistors, first calculate the total resistance in the circuit.
    • • Next, use the total resistance in the Ohm’s Law equation (E = IR) to find the individual voltage drops.
  10. 2.4.2

    Slide 11 - 2.4.2

    • Electrical Theory 26104-14
    • Voltage and Current in Parallel Circuits
    • • In a parallel circuit, the total current is equal to the sum of the branch currents.
    • • The branch current is equal to the applied voltage divided by the resistance of that branch.
  11. 2.4.2

    Slide 12 - 2.4.2

    • Electrical Theory 26104-14
    • Solving for an Unknown Current
    • • The current in branch R2 in Circuit A can be calculated as follows:
    • IT = I1 + I2
    • • Rearrange to find I2:
    • I2 = IT – I1
    • I2 = 20A – 12A = 8A
    • • The current in branch R1 in Circuit B can be calculated as follows:
    • IT = I1 + I2
    • • Rearrange to find I1:
    • I1 = IT – I2
    • I1 = 35A – 20A = 15A
  12. 2.4.3

    Slide 13 - 2.4.3

    • Electrical Theory 26104-14
    • Voltage and Current in Series-Parallel Circuits
    • • The series resistance is found by adding R1 + R2:
    • R1+2 = R1 + R2
    • R1+2 = 0.5kΩ + 0.5kΩ
    • R1+2 = 1kΩ
    • • Calculate the resistance of R3 + R4 using either the general reciprocal formula or the product over sum method, as shown here:
  13. 2.4.3

    Slide 14 - 2.4.3

    • Electrical Theory 26104-14
    • Simplified Series-Parallel Circuit
    • • Calculate the total resistance as follows:
    • RT = R1+2 + R3+4
    • RT = 1kΩ + 0.5kΩ = 1.5kΩ
    • • Apply this in Ohm’s law to find the total current as follows:
    • IT = ET/RT
    • IT = 1.5V/1.5kΩ = 1mA or 0.001A
    • • Individual voltage drops are calculated using Ohm’s law:
    • ER1 = ITR1 = 1mA x 0.5kΩ = 0.5V
    • ER2 = ITR2 = 1mA x 0.5kΩ = 0.5V
    • Next Session…
    • Kirchhoff’s Laws
  14. 3.0.0 – 3.1.0

    Slide 15 - 3.0.0 – 3.1.0

    • Electrical Theory 26104-14
    • Kirchhoff’s Laws
    • • Kirchhoff’s current law states that at any point in a circuit, the total current entering that point must equal the total current leaving that point:
    • IA + IB – IC = 0
    • 5A + 3A – 8A = 0
    • • Kirchhoff’s current law is the basis for the practical rule in parallel circuits that the total line current must equal the sum of the branch currents.
  15. 3.0.0 – 3.1.0

    Slide 16 - 3.0.0 – 3.1.0

    • Electrical Theory 26104-14
    • Application of Kirchhoff’s Current Law
    • • Applying Kirchhoff’s current law to this circuit at Point C can be shown as follows:
    • IT – I3 – I4/5 = 0
    • 6A – 2A – 4A = 0
    • • Applying Kirchhoff’s current law to this circuit at Point D can be shown as follows:
    • I3 + I4/5 – IT = 0
    • A + 4A – 6A = 0
  16. 3.2.0

    Slide 17 - 3.2.0

    • Electrical Theory 26104-14
    • Kirchhoff’s Voltage Law
    • • Kirchhoff’s voltage law states that the algebraic sum of all the potential differences in a closed loop is equal to zero:
    • EA – E1 – E2 – E3 = 0
    • 100A – 50A – 30A – 20A = 0
    • • This means that the sum of the voltage drops in a circuit is equal to the applied voltage.
  17. 3.3.0

    Slide 18 - 3.3.0

    • Electrical Theory 26104-14
    • Loop Equations
    • • Any closed path for current flow is called a loop. A loop equation specifies the voltages around the loop:
    • – E1 – E3 – E2 + ET = 0
    • – 30V – 120V – 90V + 240V = 0
    • • Voltages E1, E3, and E2 have a negative value because there is a decrease in voltage seen across each of these resistors in a clockwise direction.
  18. 3.3.0

    Slide 19 - 3.3.0

    • Electrical Theory 26104-14
    • Applying Kirchhoff’s Voltage Law
    • The voltage EB is calculated as follows:
    • – E3 – EB – E2 – E1 + EA = 0
    • Rearranged to solve for EB:
    • EB = EA – E3 – E2 – E1
    • EB = 15V – 2V – 6V – 3V
    • EB = 4V
  19. Wrap Up

    Slide 20 - Wrap Up

    • 3-2-1
    • 3 – Write 3 important things learned during class
    • 2 – Write 2 questions you have about the material
    • 1 – Write 1 thought you had about the material
    • Electrical Theory 26104-14
  20. Next Session…

    Slide 21 - Next Session…

    • MODULE EXAM
    • Review the complete module to prepare for the module exam. Complete the Module Review as a study aid.
    • Electrical Theory 26104-14