ui electrical wiringhousehold wiring fall 2019 kathmandu, nepal ui ece320 lecture 35 household...

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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

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Lecture 35


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

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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

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Saigon, Vietnam

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Kathmandu, Nepal

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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

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Lecture 35


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

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Uniform methods of wiring

Standard insulation

Safety specifications for fire risk

» Switches

» Fixtures

» Wire

» Appliances

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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

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Typical Installation-Wiring Guidelines

Color Coding

» Black Hot (+120 V)

» Red Hot (-120 V)

» White Neutral (Grounded)

» Green Ground

» Bare Ground

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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!

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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

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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

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Correct Incorrect

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Typical Installation-Distribution to Building

Black and red connections metered to monitor power usage

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Lecture 35


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

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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

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Wiring a Socket

With Tab

Both sockets set to same voltage

Without Tab

Both sockets set independently

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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

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Wiring a Single Pole Switch

ALWAYS on hot wire

Sometimes have ground, sometimes do not

Simple on/off toggle

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Wiring a Three Way Switch

ALWAYS on hot wire

Can be controlled from two points

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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

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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

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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”

ui electrical wiringhousehold wiring fall 2019 kathmandu, nepal ui ece320 lecture 35 household...

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