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Objectives

Objectives. Finish residential electrical systems Solve some example Compare electrical systems for residential and commercial building. Residential system sizing. Typically 3 wire 1 phase system 120/240 V Procedure defined by NEC article 220: Identify characteristic electrical loads

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Objectives

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  1. Objectives • Finish residential electrical systems • Solve some example • Compare electrical systems for residential and commercial building

  2. 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

  3. Homework 5 - problem 2 • Sizing the residential electrical system • Defined by NEC article 220-30 • Similar to the example we worked out • You need to collect the data for several characteristic consumers • Includes conductor sizing

  4. 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

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

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

  7. Commercial buildings-Differences Defined by NEC and local electric code! For example: No NMC (non metallic sheeted cables) wiring allowed

  8. Other differences? • Three phase • Multiple panels • More attention to expansion possibilities • More voltage levels available • For example: 277/480 and 120/208

  9. Typical Building Electrical Services

  10. Building Needs: Lighting and Duplexes • Lighting • Typically use lighting power densities for building type • Sometimes actual lighting load • Requires neutral • Duplexes • NEC/local electrical code specifies number that are required for different applications • Requires a transformer • Requires neutral wire

  11. Building Needs: HVAC/Other/Auxiliary • HVAC from system sizing • Don’t forget fans, reheat coils, etc. • Building equipment • Transportation (elevators etc.) • Food service • Specialty uses • No neutral conductor on power panel typically • Auxiliary • Energy management, security and safety, data transfer, telecommunications

  12. Electrical Systems for Commercial • Example:

  13. Panel D • Duplexes (receptacles) • Phase total 60 kVA, 14kVA (neutral) • 30 poles

  14. Transformer capacity • 200∙208∙√3 = 72 kVA ~ 75 kVA • 200∙208 / 480 = 86 A • 100 A switch • Neutral 117*208/480 = 50 A • Three #1 and one #6 aluminum (could use #4) • 100A fuse - could use 90, but likely same price

  15. Building Needs: Lighting and Duplexes • Lighting • Typically use lighting power densities for building type • Sometimes actual lighting load • Requires neutral • Duplexes • NEC/local electrical code specifies number that are required for different applications • Requires a transformer • Requires neutral wire

  16. Panel D • Duplexes (receptacles) • Main lugs only (remote protection) • 3 Phase total 60 kVA, 14kVA (neutral) • 30 poles • 60 kVA / (208V √3 ) = 167A • Select: 200 A panel • Neutral 14 kVA /120V = 117A (or if not specified 167A) • Table 11-2 for (200A, aluminum 75C, 117 neutral, but we expand to 130A like phase) • Hot wires should be 250 MCM, Neutral #2/0 aluminum • 2½ inch conduit

  17. Transformer capacity • P = I V ∙√3 =200∙208∙√3 = 72 kVA ~ 75 kVA SD switch selection: • For transformer: I1E1=I2E2 • I2 = I1E1/E2 = 200∙208 / 480 = 86 A • Select switch rated for 100 A • For 100 A rated switch select: Three #1 (aluminum) and one #1 for neutral (aluminum) • 90A fuse for phases

  18. Lighting Panel • 100A - 20 pole spaces • Hot: 65kVA/(480V∙√3) = 78 A - #2 Aluminum • Neutral: 22 kVA /277V = 79 A - #2 Aluminum • 100 A three pole fused switch • 1½ inch conduit

  19. Power Panel • No neutral? – all three pole circuits • 33 poles required – chose 42 standard size and allows for expansion • 165kVA/(480 √3) = 198 A • Choose 225A switch (could use 200 A, but you count on expansion) • 3 300 MCM aluminum wires – 2 inch conduit (in the book table you don’t have MCM 300, however it exist)

  20. Wireway • 198A + 86 A + 78 A = 362A • 400A would allow for some expansion, some would probably go to 600A • 400A three-pole switch • Six 250 MCM (unlikely to find conductors big enough to just have 3) and one #2/0 aluminum • Neutral current: maximum = 117 A, you can expand neutral too (130 A)

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

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