Download 346N_No19_Elect_Design2

Objectives
• Review conductor and conduit selection
• Learn about protection systems (basic rules)
• Learn to design Residential Electrical Systems
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:
• No more than 4 90 ° bends are allowed between
pull boxes
• In the same conduit:
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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)
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Number
Shape
Voltage rating
Current Rating
Number of poles and
wires
• Switches
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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?
• 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?
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B.
C.
D.
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)
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
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2.
3.
4.
5.
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
• Ground fault protected (GFI/GFCI)
• Switched
• Lighting
• Switches
• Ceiling Fans
Example House
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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
Bedroom 2
Laundry Closet
Kitchen
Bathroom
Mechanical
closet
Master
Bedroom
Family
room
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:
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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