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 Add lighting (3W/ft 2 ) 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

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

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

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

Electric panel - 3 wire 1 phase 120/240

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

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

Typical Building Electrical Services Voltage/Phase [V] Current [A] Building Type 120/240 1  (3w) 120/208 3  <200Residential 120/240 1  (3w) 120/208 3  Small Commercial 220/380 3  277/480 3  347/600 3  Large Commercial 5-15 kVlowVery Large Commercial

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

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

Electrical Systems for Commercial Example:

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

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

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

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 Panel D

Transformer capacity P = I V ∙√3 =200∙208∙√3 = 72 kVA ~ 75 kVA S D switch selection: For transformer: I 1 E 1 =I 2 E 2 I 2 = I 1 E 1 /E 2 = 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

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

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) MCM aluminum wires – 2 inch conduit (in the book table you don’t have MCM 300, however it exist)

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)

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