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Administrative
- Midterm follow-up due on Thursday
- Indicate why the correct answer is correct
- Quiz #7 also on Thursday
- Project Deliverable I - 4/7, II - 5/
Evaluation
Quizzes 10% Midterms 25% Projects 10% Homework Assignments 25% Participation 5% Final Exam* 25% 100%
Participation
- My assessment of your participation in the class - 5% of total grade
- How to get participation points
- Come to class and be on time
- Submit all assignments/projects on time
- Participate in class
- Come see me in my office
- Participate in all field trips (during class time)
Do you want me to post grades?
- Pros
- Lets you see how you are doing on individual items
- Compare yourself to average
- Cons
- Can’t really assess how you are doing because of grading scheme/assignments not yet handed in
- A lot of work for me/grader
Single-Phase vs. Three-Phase
Ref: Tao and Janis (2001) For three phase: P=√3 E I
Why Three-Phase?
- Larger loads
- Smaller wire sizes (because higher voltages)
- P = I^2 R
- More efficient use of neutral wire
- 3 φ needed for efficient operation of equipment
Are kWh units of energy or power?
A. Energy B. Power
Electricity Billing
- 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/ Rates/Commercial/index.htm
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
Protective Devices
- What are we protecting from?
- Circuit breakers
- Switch that responds to thermal or short circuit loads
- Fuses
- Melting metal
- Can be time-delay
Ref: Tao and Janis (2001)
Grounding
- What is electrical ground?
- Why do we ground electrical devices/systems?
- Protect equipment
- Lightening
- Protection of people
- Sometimes need ungrounded power
- If the hot side touches ground can trip a circuit
- Isolate ungrounded systems
Conductors
- Material
- Form
- Composition
- Voltage class
- Insulation
- Covering
- Temperature rating
Design issues with conductors
- Material (copper/aluminum)
- Size of conductor
- Conduit requirements
- Location
- Residential (NM,NMC,UF)
- AC and MC (with conductors)
- EMT (compression fittings set screws)
- IMC/Rigid (threaded connections)
- NEC and local codes
Other Conductor Issues
- Need conduit
- THHN – Heat resistant (90 °C), wet and dry
- THWN – Heat and moisture resistant (75 °C)
- XHHW – Used mainly for large feeders)
- Don’t need conduit
- MI – High temp., buried in concrete
- NM/NMC – Non-metallic (i.e. Romex)
- AC (or BX) – armored cable
- EMT/IC – rigid pipe Ref: Tao and Janis (2001)
Ref: Tao and Janis (2001)
If you need to put 3 350 MCM and 1
1/0 conductors in a conduit, you will
need which of the following?
A. 1.5 inch B. 2 inch C. 2.5 inch D. 3 inch
Other Issues
- In general, no more than 40% of raceway can be filled with wiring
- Need correction factor if more than three hots are in conduit (Table 11.3)
- 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
