1. Objectives
Learn about
Electricity Pricing
Electric systems

2. Electricity Billing Electrical Use (energy) Peak Demand (power)
Power factor
Which is largest portion of residential bill?
What about for commercial buildings?

3. Example: September cost of Electricity for ECJ
Assume ECJ is 120,000 ft2 and that it needs, on average, 8 W/ft2 for 8 hours a day, 6 W/ W/ft2 for 4 hours a day, and 4 W/ft2 for 12 hours a day
Use Austin Energy Large Primary summer service rate
1.5¢/kWh, $/peak kW/month
Assume no power factor charges

4. Solution large primary service $/kW $/kWh Daily $ 12.60 $ 0.015 hours$ $
hours kW
kWh 8
960
7680
demand
$12,096.00 4
720
2880
energy
$ 7,344.00 12
480
5760
TOTAL
16320
Total
$19,440.00

5. Other Pricing Strategies
Time of use pricing
Becoming more common for residential and commercial
Electricity cost related to actual cost
Requires meter
Interruptible pricing
Utility can shut off electricity for periods of time

6. Conductors Material Form Composition Voltage class Insulation Covering
Temperature rating
AWG American Wire Gage

7. Wiring method –Raceways
Electric tubes
Rigid conduits
Wire ways
Bus ducts
Underflow
Different variation

8. Design issues with conductors
Material (copper/aluminum)
Size of conductor (pg. 365)
Conduit requirements
Location
Residential or Commercial
With or without raceways
Compression fittings or set screws
Threaded connections
NEC and local codes

9. Current-Carrying Capacity
Ref: Tao and Janis (2001)

10. Tubing size
Ref: Tao and Janis (2001)

11. Other Issues
In general, no more than 40% of raceway can be filled with wiring
Why?
To prevent extensive heat up
To prevent physical installation of wires

12. Conductor Rules Explain each of the following: In the same conduit:
No more than 4 90 ° bends are allowed between pull boxes
In the same conduit:
No mixing of high- and low-voltage conductors
No mixing control and power conductors
No mixing phone and power conductors
Do place all three phases in the same conduit

13. Receptacles and switches
Receptacles (duplexes)
Number
Shape
Voltage rating
Current Rating
Number of poles and wires
Switches
Type (NEC rating)
Contact method
Speed of operation
Voltage rating
Number of poles
Method of operation
Enclosure
Duty
Other (dimming)

14. Protective Devices What are we protecting from? Circuit breakers
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

15. 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

16. Ref: Tao and Janis (2001)

17. Emergency power systems Batteries Power generators
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

18. Residential Systems 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

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

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

21. 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)

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

23. NEC about receptacles
No longer approve non-polarized and ungrounded receptacles in new installations.
Each receptacle (duplex) is rated for 1.5 A.
For 120 V: Each duplex 1.5×120 = 180W

24. 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

26. 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

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

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

29. 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