ui electrical wiringhousehold wiring fall 2019 kathmandu, nepal ui ece320 lecture 35 household...
TRANSCRIPT
1
UIECE320
Lecture 35
Household Wiring Fall 2019
Electrical Wiring
Understand the purpose and importance of the National Electric Code (NEC)
Understand basic principles of residential level power usage
Understand common electrical wiring
UIECE320
Lecture 35
Household Wiring Fall 2019
Early Distribution
Around 1920, electrical distribution largely confined to big cities
» Very little distribution in countryside/smaller cities
» Great Depression and post-WWII → Countryside distribution and interconnects
2
UIECE320
Lecture 35
Household Wiring Fall 2019
Early Distribution
Large number of small, competingelectric companies
» Distribution lines unregulated and messy
» Some companies insulated; others did not
No uniform electric code
Big fire problem
UIECE320
Lecture 35
Household Wiring Fall 2019
Saigon, Vietnam
3
UIECE320
Lecture 35
Household Wiring Fall 2019
Kathmandu, Nepal
UIECE320
Lecture 35
Household Wiring Fall 2019
Triangle Shirtwaist Factory Fire
Manhattan, New York City- March 25th, 1911
123 women and 23 men died
» Fire, smoke inhalation, falling/jumping
» Mostly aged 16-23
» Owners locked exit doors to preventunauthorized breaks/reduce theft
Led to establishment of fire code andelectric code
4
UIECE320
Lecture 35
Household Wiring Fall 2019
National Electric Code (NEC)
National Fire Protection Association
» Updated/revised every 3 years
» Current version: 2014
Intended to prevent fire
» Not for protecting people, equipment, etc.
» Purpose of fuses/breakers
Ground Fault Circuit Interrupter (GFCI)
» Protect people
UIECE320
Lecture 35
Household Wiring Fall 2019
National Electric Code (NEC)
Uniform methods of wiring
Standard insulation
Safety specifications for fire risk
» Switches
» Fixtures
» Wire
» Appliances
5
UIECE320
Lecture 35
Household Wiring Fall 2019
National Electric Code (NEC)
Not federal law, but adoptable by states
Adopted by most states
Not identical in every adopted state
» Many states that adopt amend parts of the code
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Wiring Guidelines
Color Coding
» Black Hot (+120 V)
» Red Hot (-120 V)
» White Neutral (Grounded)
» Green Ground
» Bare Ground
6
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Wiring Guidelines
Color Coding
» Green/Yellow Striped Ground
» Green/Brown Striped Ground
» Violet Ground Fault Circuit Interrupter (GFCI) Protected
Remember: If it’s not grounded, it’s hot!
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Wiring Guidelines
Wire Size Amperage Rating Typical Usage
14 Gauge12 Gauge10 Gauge8 Gauge6 Gauge
15 A20 A30 A40 A55 A
Residential LightingCommercial, Residential Fixtures, Small Appliance
Large Appliance- Clothes Dryer, Window ACLarge Appliance- Electric Range, Central AC
Large Appliance- Central AC, Electric Furnace
• Wire diameter affects maximum allowable current
• Wires are sized differently depending on usage
7
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Wiring Guidelines
Always leave slack (≈ 8 inches)
» Future electricians (or yourself) will thank you
» Wire ends break
Strip down to conductor
Limit to number/volume of wires in box
» Too much will make face plate difficult to mount
» More wires means more chance of exposed conductors contacting
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Wiring Guidelines
Correct Incorrect
8
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Distribution to Building
Black and red connections metered to monitor power usage
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation-Distribution to Building
Black and Red 180 degrees out of phase
Difference is 240 VAC RMS
-400
-300
-200
-100
0
100
200
300
400
0 0.005 0.01 0.015 0.02 0.025
Vo
lta
ge
(V
)
Time (s)
Black, Red, and Difference Voltage Waveforms
Black
Red
Difference
9
UIECE320
Lecture 35
Household Wiring Fall 2019
Typical Installation: Breaker Panel
Only point of permanent connection between ground and neutral
Single pole breakers connect to either red or black bus bar
Double pole breakers connect to both bus bars
UIECE320
Lecture 35
Household Wiring Fall 2019
Wiring a Socket
With Tab
Both sockets set to same voltage
Without Tab
Both sockets set independently
10
UIECE320
Lecture 35
Household Wiring Fall 2019
Wiring a Socket
Small hub corresponds to hot side
» Harder to accidentally make contact
Large hub corresponds to neutral side
Size difference ensures correct insertion of most plugs
UIECE320
Lecture 35
Household Wiring Fall 2019
Wiring a Single Pole Switch
ALWAYS on hot wire
Sometimes have ground, sometimes do not
Simple on/off toggle
11
UIECE320
Lecture 35
Household Wiring Fall 2019
Wiring a Three Way Switch
ALWAYS on hot wire
Can be controlled from two points
UIECE320
Lecture 35
Household Wiring Fall 2019
Purpose of Grounding
Fault to conduit
With no grounding, conduit is now hot
Touching may cause shock
Possibly no path for fault current
» Will not trip GFCI
» Will not break fuses/breakers
12
UIECE320
Lecture 35
Household Wiring Fall 2019
Purpose of Grounding
Fault to conduit
With grounding, conduit voltage is pulled to earth or “ground” potential (theoretically 0V)
Safe to touch
Path for fault current
» Will trip GFCI
» Will break fuses/breakers
UIECE320
Lecture 35
Household Wiring Fall 2019
Ground Fault Circuit Interrupter (GFCI)
Senses current imbalance using a current transformer
Trips contact plate on hot side when imbalance is high
» Typically 5 mA or more
» Trips within 2 or 3 cycles
Wet environments
Protects all outlets “downstream”