Quiz in progress

• Don’t forget to put your name on the quiz

• 1) How hard was the quiz?

A. Easy

B. Hard

C. In-between

D. What quiz?

Objectives

• Calculate billing costs (HW problem 2)

• List electrical devices

• Select conductor and conduit (HW problem 3)

• Prepare you for Assignment 1 (due in one week)

Electricity Billing (ch. 13)

• Electrical Use (energy)• Peak Demand (power)• Power factor

• Which is largest portion of residential bill?• What about for commercial buildings?• http://www.austinenergy.com/About%20Us/R

ates/Commercial/largePrimaryService.htm

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

2) What is the correct way to calculate energy consumption?

A. kWh ÷ time

B. Energy × time

C. Power × time

D. Power ÷ time

3) What is peak demand?

A. 0.018 kW/ft2 × 120,000 ft2 = 2,160 kW

B. 0.008 kW/ft2 × 120,000 ft2 = 960 kW

C. 0.018 kW/ft2 × 120,000 ft2 × 8 hr = 17,280 kWh

D. 0.008 kW/ft2 × 120,000 ft2 × 30 days = 28,800 kW

Solution

large primary service

$/kW $/kWh

Daily $ 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• HW question #2

• Interruptible pricing• Utility can shut off electricity for periods of time

Protective Devices

• What are we protecting from?• Overcurrent

• Overvoltage

• Circuit breakers• Switch that responds to thermal or short circuit loads

• Can be direct digital

• Fuses• Melting metal

• Can be time-delay

Ref: Tao and Janis (2001)

4) Why use fuses instead of circuit breakers?

A. Fuses can be used multiple times

B. Fuses are more aesthetically pleasing

C. Fuses are safer

D. Fuses cause less damage to equipment

Grounding

• What is electrical ground?• Why do we ground electrical devices/systems?

• Protect equipment• Lightening• Protection of people

• GFCI

• Sometimes need ungrounded power• If the hot side touches ground can trip a circuit• Isolate ungrounded systems

Ref: Tao and Janis (2001)

5) What is the difference between neutral and ground?

A. Neutral is a conductor, ground is an insulator

B. Current only flows through neutral when there is a problem

C. Current only flows through ground when there is a problem

D. Neutral conductor is larger than ground conductor

Conductors

• Material

• Form

• Composition

• Voltage class

• Insulation

• Covering

• Temperature rating

Design issues with conductors

• Material (copper/aluminum)• Size of conductor (pg. 145, pg. 189)• Conduit requirements (pg. 189)

• Location• Residential (NM,NMC,UF)• AC and MC (with conductors)• EMT (compression fittings set screws)• IMC/Rigid (threaded connections)

• NEC and local codes

Ref: Tao and Janis (2001)

Ref: Tao and Janis (2001)

Other Issues

• In general, no more than 40% of raceway can be filled with wiring

• Romex is allowed • Only in residential buildings• Only when concealed• Why?

Conductor Rules

• Explain each of the following:• 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)

Homework Assignment

• Q1 NEC, Q3 Conductor/Conduit Sizing

Problem 2

• Demand charges are assessed each month

• The problem involves calculating the daily cost of electricity• Demand charges ÷ 30

• Confusion about peak periodOn-Peak: 1:00 p.m. to 9:00 p.m., Monday through Friday; May 1 through October 31. 8:00 a.m. to 10:00 p.m., Monday through Sunday; November 1 through April 30.

Off-Peak: 9:00 p.m. to 1:00 p.m., Monday through Friday; all day Saturday, Sunday, Memorial Day, Independence Day, and Labor Day; May 1 through October 31. 10:00 p.m. to 8:00 a.m. Monday through Sunday; November 1 through April 30.

Summary

• Describe role of electrical system components

• Calculate billing for an electrical system given the rate structure

• Size conduit and conductors given current requirements and conductor type

• Complete HW#1