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Objectives

Objectives. Finish with Electric Systems (protective devices) HW4 (part 2) Practice circuits problems for Next Class Quiz Exams 2 (next Tuesday) FE exam. Next class QUIZ. Circuits Chapters 11 and 13. Exam 2 Tuesday (April 30 th ). In class (same as the previous one)

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Objectives

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  1. Objectives • Finish with • Electric Systems (protective devices) • HW4 (part 2) • Practice circuits problems for • Next Class Quiz • Exams 2 (next Tuesday) • FE exam

  2. Next class QUIZ • Circuits • Chapters 11 and 13

  3. Exam 2Tuesday (April 30th) In class (same as the previous one) • Circuits (chapter 10 & 11 & class examples) • AC vs. DC; single phase vs. 3 phase • Pricing (HW4 part 1) • Electric systems and wiring (chapter 11 &13 HW4 part 2)

  4. Protective Devices • What are we protecting from? • Overcurrent • Overvoltage • Circuit breakers • Switch that responds to thermal or short circuit loads • Can be bimetal, magnetic, or electronic • Reusable, remote control, compact, can be used as disconnect switch • Fuses • Melting metal • Self destructive, larger

  5. Why use fuses instead of circuit breakers? • Fuses can be used multiple times • Fuses are more aesthetically pleasing • Fuses are safer • Fuses cause less damage to equipment

  6. Ref: Tao and Janis (2001)

  7. Motor starters • ON-OFF switches are NOT for motors • Motor circuit-rated switches • Reduce the current during the start until the motor rich full speed • Protect the motor form overload • Emergency power systems Batteries Power generators Reading Assignment: Chapter 11

  8. Residential Systems(NEC Article 220-Branch Circuit, Feeder and Service Calculations) • Very little variation between different houses • Many similarities to commercial buildings • Particularly as you get close to end uses • Need to be watchful for unusual circumstances

  9. Wiring from panel to: receptacles, lighting, ceiling fan,….. Feeders and conduit House branch circuits Electric panels

  10. Electric panel - 3 wire 1 phase 120/240

  11. Procedure • Analyze building needs • Determine electrical loads • Select electrical systems • Coordinate with other design decisions • Prepare plans and specifications

  12. List of needs • Appliances (incl. HVAC) • Receptacles • Ground fault protected (GFI/GFCI) • Switched • Lighting • Switches • Ceiling Fans

  13. Example House • Master Bedroom • Bathrooms • Entry and Outdoor (AC compressor) • Bedrooms • Dining and Mechanical Closet (resistance heat) • Kitchen (appliance circuits, range, oven) • Family • Garage/Laundry/Closet (resistance water heater, dryer)

  14. Outdoor Bathroom Closet Bedroom 2 Laundry Kitchen Bathroom Mechanical closet Family room Master Bedroom Entry Bedroom 3 Dining Garage

  15. Residential system sizing Typically 3 wire 1 phase system 120/240 V • Procedure defined by NEC article 220: • Identify characteristic electrical loads • Add lighting (3W/ft2) • Add two 20 Amps circuits for kitchen • Add one 20 Amps circuit for laundry • Electricity for HVAC equipment based on requirement for heating or cooling

  16. Summary of Power Sizing • Include enough capacity for heating and cooling • Work through kitchen and then other rooms • Include any items that are unusual • Take first 10 kVA and then 40% of remaining load

  17. Panel Sizing • Find panel power usage and neutral usage • Size panel conductors and associated conduit and switches

  18. Electric panel - 3 wire 1 phase 120/240

  19. Wiring from panel to: receptacles, lighting, ceiling fan,….. Feeders and conduit House circuits Electric panels

  20. Outdoor Bathroom Closet Bedroom 2 Laundry Kitchen Bathroom Mechanical closet Family room Master Bedroom Entry Bedroom 3 Dining Garage

  21. Homework 4 - problem 2 • Sizing the residential electrical system • Defined by NEC article 220-30 (BOOK chapter 13) • Similar to the example we worked out • You need to collect the data for several characteristic consumers • Includes conductor sizing

  22. HW4 (problem 1)

  23. Circuit problems (for practicing)Start with problems that Yune provided:http://www.ce.utexas.edu/prof/Novoselac/classes/ARE346N/Handouts.html

  24. Example problem 1 What is the potential difference (voltage) across the 20-Ω resistor? a. 3.2 V b. 7.8 V c. 11 V • 5.0 V • 8.6 V

  25. Example problem 2

  26. Example problem 3 NOTE: After t = 5t, the capacitor acts like an open circuit

  27. Example problem 4 NOTE: Time constant of the circuit is t = RC = 15 ms. Time constant is the time to charge capacitor to 63%. [1- e-1]. To charge more (80%) you need more time.

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