1) What is the NEC?

A. National Electrical Code

B. National Electrical Corporation

C. A kind of cookie

D. National Energy Code

Objectives

• Use CPS website - Copernicus

• Submit ASHRAE form and get textbook

• Understand grade on homework 0 and quiz 1

• Complete homework 1

• Size residential electrical system (NEC 220-30)

• List differences between residential and commercial systems

Copernicus

• http://utwired.engr.utexas.edu/cps/

• Questions and answers

• Absences and lates

ASHRAE

• Can still bring it to me if you want a copy

• You are responsible for sending it in and following up with ASHRAE

• Chapter is Austin

• Don’t worry about UT address (zip = 78712)

• 3 options for handbook (IP, SI, CD)

• Money that you send ASHRAE needs to include $16 dues

Quiz 1 and HW 0

• Both graded• Solutions to Quiz 1 on class website• Grader very generous and I upped grade in a few

cases (avg. ?, st. dev. ?)• Will give back at end of class • Can drop lowest grade

• HW 0 (avg. ?, st. dev. ?)• Come see me to see your score (I will not hand back until

end of semester)• Extremely generously graded

Residential Systems

• Very little variation

• Many similarities to commercial buildings• Particularly as you get close to end uses

• Need to be watchful for unusual circumstances

Procedure

1. Analyze building needs

2. Determine electrical loads

3. Select electrical systems

4. Coordinate with other design decisions

5. Prepare plans and specifications

List of needs

• Appliances (incl. HVAC)

• Receptacles• Ground fault protected (GFI/GFCI)• Switched

• Lighting• Switches

• Ceiling Fans

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)

2) Where are receptacles grounded?

A. Kitchen near sink only

B. Kitchen, bathroom only

C. Kitchen, bathroom, outside only

D. Bedrooms

Ref: Tao and Janis (2001)

3)Why do we include 65% of the heating electrical load and 100% of the

air conditioning load ?A. Air conditioning happens during periods of

peak electrical demand.

B. Other electrical uses contribute to heating and not to air conditioning.

C. Furnaces are often more closely sized to match the heat loss of a house.

D. The NEC was designed for homes in Southern climates.

4)A residential electrical system is sized to meet:

A. 40% of the maximum load

B. 50% of the maximum load

C. More than 50% of the maximum load

D. It depends.

Summary

• 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

Commercial buildings-Differences

• 5)Why do you specify conduit for all conductor in commercial buildings

A. Three phase power requires conduit

B. Higher voltage requires conduit

C. Conduit looks pretty

D. No NMC wiring allowed

Other differences?

• Three phase

• Multiple panels

• More attention to expansion possibilities

• More voltage levels available

Typical Building Electrical ServicesVoltage/Phase[V]

Current

[A]

Building Type

120/240 1120/208 1

<200 Residential

120/240 3120/208 3

200-800 Small Commercial

240/480 3277/480 3347/600 3

400-2000 Large Commercial

5-15 kV Very low Very 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

Selecting Electrical Systems

• MLO/MCB

• Aluminum wiring

• Duplexes (receptacles)

• Main Lugs Only (remote protection)

• Phase total 60 kVA, 14kVA (neutral)

• 30 poles

Panel D

6) How do you calculate current flow through a neutral conductor in a 3 system?

A. I =√3 E P

B. I =P/ (√3 E )

C. I =P/ E

D. I= E P

• Duplexes (receptacles)• Main lugs only (remote protection)• 3 Phase total 60 kVA, 14kVA (neutral)• 30 poles• 60 kVA / (208V √3 ) = 167A• 200A panel• Neutral 14000/120 = 117A• Table 11-2

• Hot wires should be 250 MCM, Neutral #2/0 aluminum• 2½ inch conduit

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

Ref: Tao and Janis (2001)

Ref: Tao and Janis (2001)

Summary

• Size residential systems

• List differences between commercial and residential systems

• Differentiate and size commercial panels