Objectives Learn about Electricity Pricing Electric systems

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

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, 12.60 $/peak kW/month Assume no power factor charges

Solution large primary service $/kW $/kWh Daily $ 12.60 $ 0.015 hours $ 12.60 $ 0.015 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

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

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

Wiring method –Raceways Electric tubes Rigid conduits Wire ways Bus ducts Underflow Different variation www.hhrobertson.com/

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

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

Tubing size Ref: Tao and Janis (2001)

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

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

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)

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

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

Ref: Tao and Janis (2001)

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

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

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

List of needs Appliances (incl. HVAC) Receptacles Lighting 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)

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

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

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

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

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