Download Basic Electrical Wiring

UNIT-I
Wiring Tools
Learning Objectives
• Identify the basic hand tools used in the electrical trades.
• Select the essential tools for each specific job.
• Maintain and use these tools safely.
• List factors to consider when purchasing hand tools.
The Electrician’s Tool Pouch
•
The Electrician’s tool pouch is essential in that it
helps kept electrical tools organized. The tool
pouch allows the right tools at hand which
makes the job more efficient.
•
The electrician must have proper tools for the
job.
•
Tools must be maintain and kept in good
working condition.
•
Certain tools are essential, and without them
the electrician should not attempt to do any
type of wiring.
•
Listed are the basic hand tools that are
essential to electrical wiring.
Electrical Specific Hand Cutting Tools
Needle-nose pliers
• Forming loops on small conductors
• Cutting and stripping small conductors
Lineman’s pliers (side cutters)
• Cutting large conductors
• Forming loops on large conductors
• Pulling and holding large conductors
Diagonal pliers (dykes)
• Cutting small conductors
• Cutting conductors in limited spaces
Wire strippers
• Stripping insulation from conductors
• Cutting small conductors
• Crimping wire lugs
Electrical Specific Hand Tools
Tap tool
• Equipping drill holes with bolt threads
• Retapping damaged threads
• Determining bolt size
Center punch
• Making center tap in wood or metal for
drilling
Flat-blade screwdriver
• Installing and removing slot-head screws
Phillips screwdriver
• Installing and removing phillips-head
screws
Electrical Specific Hand Tools
Slip-joint pliers
• Holding couplings and conductors
• Tightening couplings and conductors
Magnetic torpedo level
• Leveling conduit and equipment
Keyhole saw
• Cutting holes in plasterboard for circuit
boxes
Conduit reamer
• Reaming burrs from cut conduits and EMT
Electrical Specific Hand Tools
Hacksaw
• Cutting large conductors and cables
• Cutting conduit, metal, or bolts
Adjustable wrenches
• Used for turning bolts, nuts, and small
pipe fittings
Steel measuring tape
• Measuring conduit and cable
Nut driver
• Installing and removing nuts and bolts
• Tightening and loosening nuts and long
bolts
Electrician's Essential Tools
Electrician’s hammer
• Diving and pulling nails
• Opening wooden crates and breaking
plasterboard
Circuit tester
• Checking circuits for power
• Checking fuses and breakers
Electrician’s knife
• Opening paper cartons
• Stripping cables and large conductors
Hex key set (Allen wrenches)
• Installing and removing Allen screws
Tools Used for Specialty Work
Steel fish tape and reel
• Pulling conductors through conduit
• Pulling cables through insulated walls
Rotating speed screwdrivers
• Used for trim work, installing switch and
receptacles
Conduit bender
• Bending conduit for conductor installation
Sheet metal Cutters
• Used for cutting and trimming sheet metal
Rules for care of hand tools
•
There are many more hand and power tools
that electricians will use in residential and
commercial wiring.
•
All tools should be used only for the purpose
intended.
•
It is the electrician’s responsibility to keep his
or her tools sharp, clean, and lubricated.
•
•
A well maintained tool has a longer life and is
safer than an improperly maintained tool.
Repair tools when possible, but discard worn
or damaged tools.
Factors For Purchasing Tools
Factors to consider when purchasing
tools are size, design, and quality.
• Always purchase the correct sized tools
for the work to be done.
• Tools should be designed specifically for
electrical work. Ex: Insulated handles,
hammers with straight claws.
• The purchase of quality tools last longer
which saves replacement cost.
Remember
• Select the right tool for the job.
• Keep tools clean, lubricated, and in good working condition.
• Purchase good quality tools they are safer and will last longer.
• Repair tools when possible, but discard worn or damaged
tools.
UNIT-II
Electrical wiring Accessories
How does electricity get to your
house?
Generation facilitiesMost electricity is made by turbine blades rotating at speeds high enough to
produce electricity in a generator. The blades can be turned by water, steam
or wind.
Switchyard
 High-voltage switchyard- The electricity flows through
metal conduction to a switchyard, where a
transformer steps up voltage for transmission.
Transmission Lines
 Transmission lines -Transmission lines can efficiently
carry high-voltage electricity over long distance to
substations.
Substations
 Substations -At substations, electricity is
stepped down so it can travel over smaller
distribution lines to homes and businesses.
Distribution Lines
• Distribution lines -Distribution lines carry
electricity to neighborhoods.
Transformer
 Transformer -an electric-pole transformer reduces the
voltage to a level that can be used in homes
Service Drop and Meter
 The line that connect from the overhead street power lines to
your house is called the Service Drop.
 The utility company owns and is responsible for the Service drop
and any wires before they enter the Weatherhead.
Weatherhead
• The weatherhead prevents any water, snow or
moisture to enter the system and travel down
the wires to the panel.
Service Panel
• After the wires enter the weatherhead they
travel down the large conduit to the Service
panel.
• From the panel, the power is distributed to
the different circuits throughout the house.
Circuits
• A circuit breaker is an automatically
operated electrical switch designed to
protect an electrical circuit from
damage caused by overload or short
circuit.
• Its basic function is to detect a fault
condition and, by interrupting
continuity, to immediately discontinue
electrical flow.
• Unlike a fuse, which operates once and
then has to be replaced, a circuit
breaker can be reset (either manually or
automatically) to resume normal
operation.
Main components in residential
application
• Lights and Switches
• Receptacles/outlets
• Hardwired appliances
Lights and switches
• Lights are typically run with
14 gauge wire.
• In a single pole application
when one switch is operating
the light, 14-2 wire is used.
• In a 3-way situation when a
two switches are used to
operate one light, then 14-3
wire must be used.
Single pole switch wiring
3-way switch wiring
Outlets
• An electrical outlet, also called a receptacle, is
the flush mounted plate we plug our electrical
appliances into.
15 amp outlet
20 amp outlet
15 amp and 20 amp Outlets
• 15 amp outlets are run with 14 gauge wire.
• 20 amp outlets are run with 12 gauge wire.
• 20 amp outlets are recognizable by the Tshaped slot on the neutral side of the outlet.
15 amp
20 amp
Wiring an Outlet
 There is usually more than one outlet on a circuit, so the
above diagram explains how to wire an outlet in the
middle of circuit and also how the outlet on the end is
wired.
GFCI
• GFCI stands for Ground Fault Circuit Interrupter.
• GFCI outlets are required by code in bathrooms
and kitchens because both areas have the
chance of getting wet.
220-240 amp outlets
• Some appliances in your home
will require a 220 volt outlet.
– Kitchen Stove
– Cloths Dryer
Hard wired
• Some appliances or fixtures are hard wired to
the power supply. This means they don’t plug
in, but they have the wires from the wall tied
directly to them.
• Some examples might include
– Dish waser
– Well pump
– Furnace/boiler
– Hot water heater
– Smoke detectors
Some wiring tips
 Always flip a breaker off before you do any work
on a circuit!
 Smoke detectors are required by code in any
residence.
 Lighting circuits should be wired separately from
other circuits so if a breaker is tripped, you still
have lights.
 By code switches have to be installed 48 inches
from the floor.
 By code outlets have to installed 18 from the
floor.
Tips continued
 Install outlets with the ground hole facing up so you
will never drop something across the hot and neutral
lines.
 When drilling studs for running wire in walls, always
drill in the center of the stud to minimize the risk of
hitting a wire with a nail.
 Remember that only 50 milliamps of electricity across
your chest, stop your heart.
 Use insulated tools.
 Never cut across a hot and neutral with any tool.
(lineman's pliers, sawzall) It will trip the breaker and
ruin the tool.
Tips continued
• If a wire has to be run too close to the edge of
a stud, then use a metal protective plate in
case someone drives a nail in that area.
• When wiring switches and outlets,
use needle nose pliers to bend
C-Shaped hooks on the bare end of the wire.
• Wrap the end of the wire clockwise onto the
screw so that when you tighten the screw the
hook tightens around the screw instead of
loosening up.
Tips continued
• Remember that to become an
electrician you must complete a
4 year apprenticeship program, thousands of
hours of on-the-job experience and hundreds
of hours in the classroom.
• So don’t assume that because you have seen
this presentation you can wire a house!
Dedicated circuits
 For larger and more sensitive appliances, it is a good idea
to run a dedicated circuit which means, only that
appliance is on that circuit, nothing else. This minimizes
the chance of the breaker being tripped.
 Some examples of appliances are:








Refrigerator
Air Conditioners
Furnace/boiler
Electric stove
High-end Electronics (as seen in hospitals)
Well pump
Hot water heater
Anything with a large electrical draw
UNIT-III
Electrical Wiring Joints
•
•
•
•
•
•
•
Safety
Standards
Wiring Considerations
Wire Terminations
Coaxial Cable
Wiring Installations
Wiring Diagrams
Safety
• Lethal Current
• Safety Precautions
MElec-Ch2 - 41
Lethal Current
• Fundamental policy of the USPS is SAFETY
• Human Body
– Resistance – 4 KΩ (moist skin) to 24 KΩ (dry skin)
– Safe current (through chest) – less than 20 milliamps
– E = 120 VAC
R = 4 KΩ
– I = 30 milliamps - NOT SAFE
I=?
– Don’t want current through chest cavity (may be lethal)
MElec-Ch2 - 42
Safety Precautions
• Turn circuit off
– Disconnect service cord
– Disconnect negative battery cable
• If must work on live AC circuit
– Need 2nd safety person
• Remove metal jewelry
• Know your boat and its wiring
• Use outlet tester on AC outlets
• Use 3-wire extension cord from GFI outlet
MElec-Ch2 - 43
Standards
• American Boat and Yacht Council (ABYC)
– AC and DC Electrical Systems is E-11
– Minimum standards
• Construction
• Repair
• Marine Dept. of Underwriters Laboratory
– Test and certify commercial products
– Safety, not function
MElec-Ch2 - 44
Wiring Considerations
• Conductors
• Wire Types
• Wire Size
• Wire Insulation
• Wire Color Code
MElec-Ch2 - 45
Conductors
• Connects power sources to power loads
• Characteristics
– Safe
– Dependable
– Efficient (minimal voltage drop)
• Boat environment
– Worse than either house or car
– High humidity
– Vibration
– Corrosive conditions
MElec-Ch2 - 46
Wire Types
• Marine Grade
– Type 3 is recommended
• Stranded copper
– Tinned is preferred
MElec-Ch2 - 47
Wire Size
• 3% voltage drop
– Critical circuits (Nav lights)
– Electronic Equipment
• 10% voltage drop
– Cabin lights
– Motorized Equipment
• Minimum size AWG # 16
MElec-Ch2 - 48
Wire Has Resistance
12 VDC
0.1 Ώ
10A
0.1 Ώ
V
What Voltage?
An. 10 VDC
• Inadvertent Resistors
– Wire too small (min of #16 - properly size using table)
– Bad connections (or corroded connections)
• Clean and tighten battery connectors
• Tighten lug screws and inspect wire to lug connection
– Why do wires get warm / hot?
• Low resistance circuits pass high current (P = I2 x R)
• Wires can account for much of the overall resistance
MElec-Ch2 - 49
Wire Size Comparison
#16 top to #10 bottom
#2 top to #10 bottom
MElec-Ch2 - 50
Copper Wire Characteristics
MElec-Ch2 - 51
12- VDC Wire Size Selection
MElec-Ch2 - 52
12 VDC Wire Size Selection
MElec-Ch2 - 53
120 VAC Wire Size Selection
MElec-Ch2 - 54
What Size Wires?
B
MElec-Ch2 - 55
Step 1
B
What current to Load?
I = 10 Amps
P = E * I I = P / E I = 1200/120
From Table 2-1 – For 10A need #16 wire
From Table 2-3 – Maximum of 44 feet (for 10A in #16 wire)
MElec-Ch2 - 56
Step 1 Answers
AMPACITY
10 Amperes
#16 AWG TW
by Table 2-1
B
for 3% voltage drop
44 feet maximum
by Table 2-3
MElec-Ch2 - 57
Step 2
B
What current to Inverter? Iload = 100 Amps @ 12 V
Iload = Iout = Iin *0.91
Iin = Iout / 0.91 = 100 / 0.91 = 110 Amps
From Table 2-1 – For 110A need #1 wire
From Table 2-3 – Maximum of 14 feet (for 110A in #1 wire)
MElec-Ch2 - 58
Step
2
Answers
AMPACITY
110 Amperes
#1 AWG TW
by Table 1
B
for 3% voltage drop
14 feet maximum
by Table 2-2A
MElec-Ch2 - 59
Wire Insulation
• AC cables must be type UL 1426 BC
– 600 volt insulation
– Gasoline and Oil resistant
– Won’t absorb moisture
• DC wires & cables must be Marine Grade
– 600 volt insulation
– Gasoline and Oil resistant
– Won’t absorb moisture
• Color coded wires
MElec-Ch2 - 60
Wire Color Code
Color
AC (Hot)
AC (Neut) AC (Gnd)
Black
X
White
X
Green (may have a yellow stripe)
Red
X2
Yellow
DC +
DC -
X1
X
X
X1
Footnotes:
1 – Yellow preferred for DC negative to avoid confusion with AC Hot wire
2 – 2nd hot wire in 220 VAC is Red
MElec-Ch2 - 61
MElec-Ch2 - 62
Wire Terminations
• Crimping
– Special Tool
– Approved Marine Connectors
– Use of Ratcheting Tool
• Solder
• Heat-shrink Tubing
MElec-Ch2 - 63
Wire Terminals
MElec-Ch2 - 64
Ratcheting Crimper
YES
NO
MElec-Ch2 - 65
Ratcheting Tool Use
• First select appropriate connector
• Strip insulation length of stem plus 1/16”
• Insert stripped end all way into terminal
– End should extend 1/16”
• Place terminal in same color slot
– First crimp end of terminal barrel nearest ring
– Then crimp wire end of terminal barrel
• Check the connection with a solid tug
MElec-Ch2 - 66
Soldering
• Terminal connection can’t be only soldered
– Must also be crimped
• Soldering is normally not required
– Crimped connectors are acceptable to ABYC
– If solder, apply only to ring end of terminal
• Solder changes stranded wire into solid
– Stranded wire is flexible
• Use 40% lead / 60% tin, rosin core solder
• Battery lugs may be only soldered
MElec-Ch2 - 67
Heat-Shrink Tubing
Application Steps
MElec-Ch2 - 68
Coaxial Cable
•
•
•
•
Antenna cable
Radio coax is 50 ohm with PL-259
Radio cable is cut to length
Want attenuation under 3 db
• TV cable is 75 ohm with “F” connectors
• GPS cable is not cut to length
– Coil excess in 1-foot loops
MElec-Ch2 - 69
Coaxial Cable Information
MElec-Ch2 - 70
Soldering PL-259 Connector
MElec-Ch2 - 71
Wiring Installation
•
•
•
•
Basic Considerations
Distribution Panel
Fuses / Circuit Breakers
Branch Circuits
– Wire
– Outlets
– Switches
• Grounding Systems
• Bonding Systems
MElec-Ch2 - 72
Basic Considerations
• Must have source and return wires
– Return wires to a common point
– May use feeder wire from power panel for:
• engine, helm console, etc.
• Wires above flood level of bilge
– Waterproof if in bilge
• Insulated support every 18”
• Twist DC wires within 1 meter of compass
MElec-Ch2 - 73
Distribution Panel
• Central location of Circuit Breakers / Fuses
– All branch circuits from this location
• AC and DC may be combined in one panel
• All equipment / circuits should go to panel
– Not direct to battery (except bilge pump)
• Noise interference suppression covered in Section 7
MElec-Ch2 - 74
DC / AC Power Panel
Front View
MElec-Ch2 - 75
Inside Power Panel
Buss Bars
DC Side
MElec-Ch2 - 76
Fuses and Circuit Breakers
• Used to protect wiring from over current
– In positive or hot wire
• Newer boats use circuit breakers
– Initially more expensive
• Replace blown fuse with correct rating
• Circuit Breakers should be Marine Grade
– Trip free
– Manual reset
MElec-Ch2 - 77
Branch Circuits - Wires
• Minimum size is 16 AWG
– See Wire Selection Tables
– For AC normally #14 for 15A and #12 for 20A
• Must terminate in closed electrical box
• Of sufficient length
• DC negative returned to DC Panel
– May use several negative feeder terminals
• AC neutrals returned to AC Panel
• Bonding system never used as return wire
MElec-Ch2 - 78
Branch Circuits - Outlets
• 120 VAC outlets must be 3-wire polarized
– Black (hot) to brass or copper colored terminal
• Outlet wires must have crimp terminals
• GFI outlets
– Required on weather deck, head, galley and
machinery spaces
– Good practice for all AC outlets to be GFI
– Trip at 5 milliamps
• Different outlets for AC and DC power
MElec-Ch2 - 79
12 VDC
DC Outlet
(Receptacle)
DC Plug
Outlets and Plugs
120 VAC
120 VAC
120 VAC
15 A Outlet
GFI 15 A
Outlet
20 A Outlet
AC Plug 15 A
AC Plug 20 AMElec-Ch2 - 80
Branch Circuits - Switches
• Modern panels use Circuit Breakers
– Which also double as switches
• Switches / Circuit Breakers
– Must be Marine Grade
– Rated for the voltage and current controlled
– Interrupt the positive (DC) or hot (AC) leg
• Battery Switch
– Designed for high current service
– Not located in engine or fuel-tank compartments
MElec-Ch2 - 81
Grounding System
• Ground is potential of water around boat
– Or potential of earth’s surface
• DC – Ground Battery negative terminal(s)
– Also engine block
– Wire color is Yellow (or Black)
• AC – Transformer center tap on shore
– Also connected to ground rod at transformer
– Wire color is Green and uninterrupted wire
• Isolation transformers and galvanic isolators are exception
and covered in Chapter 4 on AC
• Engine, DC negative & AC ground connected
MElec-Ch2 - 82
Bonding System
• For lightning protection
– More in Chapter 6
• All metal objects should be bonded
– Keeps all metal at zero potential
– Engine blocks
– Battery negative terminals
• Non-current carrying wire
• Through-hull fittings
– ABYC now recommends they be bonded
– Electrically isolated from metal hull MElec-Ch2 - 83
Bonding Diagram
MElec-Ch2 - 84
Wiring Diagrams
• Elements of a Good Wiring Diagram
– Documents boat’s electrical layout
– Should be kept current
– Used for troubleshooting
• Component Identification
– Physical objects to their symbol
– Wires are color coded
MElec-Ch2 - 85
Wiring Diagram Symbols
Wire (insulated, metal conductor)
Incandescent Light
Wires crossing (but NOT connected)
Alternate symbol for Light
Wires connected (at dots)
Circuit Breaker
Battery (long line on top is positive)
Switch, single pole, single throw (SPST)
Switch, single pole, double throw (SPDT)
Switch, double pole, single throw (DPST)
Fuse
Ground
Male Connector
Female Connector
MElec-Ch2 - 86
Simple DC Wiring Diagram
MElec-Ch2 - 87
Summary
• Circuits should be off when working on them
• Use only marine grade properly sized wires
– Tables will help determine proper wire size
– Minimum wire size is #16 AWG
• Use wire terminations and ratcheting crimper
• DC circuits are 2 dedicated wires
– Waterproof wire connection in bilge
• AC circuits are 3 dedicated wires
– GFCI in galley, head, machine spaces & weather deck
• Separate Grounding & Bonding systems required
• Keep wiring diagram current
MElec-Ch2 - 88
UNIT-IV
ELECTRICAL LAMP CIRCUITS
Ohm’s Law
I=V/R
Georg Simon Ohm (1787-1854)
I
= Current (Amperes) (amps)
V
= Voltage (Volts)
R
= Resistance (ohms)
Voltage: a force that
pushes the current
through the circuit (in
this picture it would be
equivalent to gravity)
Resistance: friction that
impedes flow of current
through the circuit
(rocks in the river)
Current: the actual
“substance” that is
flowing through the
wires of the circuit
(electrons!)
Would This Work?
The Central Concept: Closed Circuit
circuit diagram
Scientists usually draw electric circuits using symbols;
cell
lamp
switch
wires
Simple Circuits
• Series circuit
– All in a row
– 1 path for electricity
– 1 light goes out and the
circuit is broken
• Parallel circuit
– Many paths for electricity
– 1 light goes out and the
others stay on
1
2
PARALLEL CIRCUIT
• Place two bulbs in parallel. What do you
notice about the brightness of the bulbs?
• Add a third light bulb in the circuit. What do
you notice about the brightness of the bulbs?
• Remove the middle bulb from the circuit.
What happened?
measuring current
Electric current is measured in amps (A) using
an ammeter connected in series in the circuit.
A
measuring current
This is how we draw an ammeter in a circuit.
A
A
SERIES CIRCUIT
PARALLEL CIRCUIT
measuring voltage
The ‘electrical push’ which the cell gives to the current
is called the voltage. It is measured in volts (V) on a
voltmeter
V
measuring voltage
This is how we draw a voltmeter in a circuit.
V
SERIES CIRCUIT
V
PARALLEL CIRCUIT
The circuit is no longer complete, therefore current can not flow
The voltage decreases because the current is decreased
and the resistance increases.
The current remains the same. The total resistance drops in a
parallel circuit as more bulbs are added
The current increases.
Series and Parallel Circuits
• Series Circuits
– only one end of each component is connected
– e.g. Christmas tree lights
• Parallel Circuits
– both ends of a component are connected
– e.g. household lighting
measuring voltage
Different cells produce different voltages. The
bigger the voltage supplied by the cell, the bigger the
current.
Unlike an ammeter, a voltmeter is connected across
the components
Scientist usually use the term Potential Difference
(pd) when they talk about voltage.
series circuit
• voltage is shared between the components
3V
1.5V
1.5V
parallel circuit
• voltage is the same in all parts of the circuit.
3V
3V
3V
Voltage, Current, and Power
• One Volt is a Joule per Coulomb (J/C)
• One Amp of current is one Coulomb per second
(6.24 x10^18 electrons/second).
• If I have one volt (J/C) and one amp (C/s), then
multiplying gives Joules per second (J/s)
– this is power: J/s = Watts
• So the formula for electrical power is just:
P = VI: power = voltage  current
• More work is done per unit time the higher the
voltage and/or the higher the current
UNIT-V
GROUNDING SYSTEMS
The objective of a grounding system are:
1. To provide safety to personnel during normal and fault
conditions by limiting step and touch potential.
2. To assure correct operation of electrical/electronic devices.
3. To prevent damage to electrical/electronic apparatus.
4. To dissipate lightning strokes.
5. To stabilize voltage during transient conditions and to
minimize the probability of flashover during transients.
6. To divert stray RF energy from sensitive audio, video,
control, and computer equipment.
A safe grounding design has two objectives:
1. To provide means to carry electric currents into
the earth under normal and fault
conditions without exceeding any operating
and equipment limits or adversely affecting
continuity of service.
2. To assure that a person in the vicinity of
grounded facilities is not exposed to the
danger of critical electric shock.
The PRIMARY goal of the grounding
system throughout any facilities is
SAFETY.
Why ground at all?
PERSONNEL SAFETY FIRST
EQUIPMENT PROTECTION SECOND
What are the three main types
of grounding?
The three main types are:
• EQUIPMENT GROUNDING (SAFETY)
• SYSTEM GROUNDING
• LIGHTNING/SURGE GROUNDING
Earth / Ground Basics
Types of Grounding Systems
• Many different types available
• Choice depends on local
conditions and required
function
• Simplest form is a single stake
• Mostly used for:
– Lightning protection
– Stand alone structures
– Back-up for utility ground
Ground rod
Earth / Ground Basics
Types of Grounding Systems
• ground rod group
• typically for lightning
protection on larger
structures or protection
around potential hotspots
such as substations.
Ground rod group
Earth / Ground Basics
Types of Grounding Systems
• For areas where there is rock
(or other poor conducting
material) fairly close to the
surface ground plates are
preferred as they are more
effective
Ground plate
Earth / Ground Basics
Types of Grounding Systems
• A ground mesh consists of
network of bars connected
together, this system is often
used at larger sites such as
electrical substations.
Ground mesh
Soil Characteristics
• Soil type. Soil resistivity varies widely depending
on soil type, from as low as 1 Ohmmeter for
moist loamy topsoil to almost 10,000 Ohmmeters for surface limestone.
• Moisture content is one of the controlling
factors in earth resistance because electrical
conduction in soil is essentially electrolytic.
Cable(Earthing conductor)
Clamp
Test link
Rod(Earthing electrode)
Rod coupler
Recommended values of earth resistance
system
Recommended earth
resistance(ohm)
Light current
0.5-1
Low voltage
5
Medium
voltage
2.5
High voltage
0.5
Substation earthing system
•Step & Touch voltage
•Grounding grids
Step and touch voltages
Step potential
• “Step potential” is the
voltage
between the feet of a person standing near
an energized grounded object.
• It is equal to the difference in voltage, given
by the voltage distribution curve, between
two points at different distances from the
“electrode.”
• A person could be at risk of injury during a
fault simply by standing near the grounding
point.
Touch potential
• “Touch potential” is the voltage between the
energized object and the feet of a person in
contact with the object.
• It is equal to the difference in voltage
between the energized object and a point some
distance away.
• The touch potential could be nearly the full
voltage across the grounded object if that object
is grounded at a point remote from the place
where the person is in contact with it.
Ground Testing Methods (1)
Resistivity Measurement
The purpose of resistivity measurements is to quantify the
effectiveness of the earth where a grounding system will be
installed.
Differing earth materials will affect the effectiveness of the
grounding system.
The capability of different earth materials to conduct current
can be quantified by the value E (resistivity in W.m).
Resistivity measurements should be made prior to installing a
grounding system, the values measured will have an effect on
the design of the grounding system.
Ground Testing Methods (1)
Resistivity Measurement ( Wenner method)
Resistivity measurements are performed by using a
four wire method.
Used to determine
which KIND of
earthing should be
used, so BEFORE
placing earth stakes
Ground Testing Methods (1)
Resistivity Measurement
From the indicated resistance value RE, the soil
resistivity is calculated according to the equation :
 E = 2  . a . RE
E
RE
a
...... mean value of soil resistivity (W.m)
...... measured resistance (W)
...... probe distance (m)
Resistance of driven rods:
• The Ground Resistance (R) of a single rod, of diameter (d) and driven
length (i) driven vertically into the soil of resistivity (ρ), can be calculate
as follows:
   8l  
R
ln    1

2l   d  
where:
ρ
Soil Resistivity in m
l
Buried Length of the electrode in m
d
Diameter of the electrode in m
The rod is assumed as carrying current uniformly along its rod.
• Examples
(a) 20mm rod of 3m length and Soil resistivity 50 Ω-m .....R=16.1 Ω
(b) 25mm rod of 2m length and Soil resistivity 30 Ω-m .....R=13.0 Ω
• The resistance of a single rod is not sufficiently low.
• A number of rods are connected in parallel.
• They should be driven far apart as possible to
minimize the overlap among their areas of
influence.
• It is necessary to determine the net reduction in the
total resistance by connecting rods in parallel.
• The rod is replaced by a hemispherical electrode
having the same resistance.
Rod Electrodes in Parallel
• If the desired ground resistance cannot be achieved with
one ground electrode, the overall resistance can be
reduced by connecting a number of electrodes in parallel.
• These are called “arrays of rod electrodes”.
• The combined resistance is a function of the number and
configuration of electrodes, the separation between
them, their dimensions and soil resistivity.
• Rods in parallel should be spaced at least twice their
length to utilize the full benefit of the additional rods.
• If the separation of the electrodes is much larger
than their lengths and only a few electrodes are in
parallel, then the resultant ground resistance can be
calculated using the ordinary equation for
resistances in parallel.
• In practice, the effective ground resistance will
usually be higher than this.
• Typically, a 4 spike array may provide an
improvement of about 2.5 to 3 times.
• An 8 spike array will typically give an improvement
of may be 5 to 6 times.
Earth clamping 1
AT-090H
AT-090H
Earth clamping 2
AT-087J
AT-089J
AT-093J
METHODS OF DECREASING GROUND
RESISTANCE
• Decreasing the ground resistance of a
grounding system in high resistivity soil is
often a formidable task.
• Recently, some new methods have been
proposed to decrease ground resistance.
1-Chemical Rods
• Chemical rods are electrodes with holes along their
length, filled with mineral salts.
• The specially formulated mineral salts are evenly
distributed along the entire length of the electrode.
• The rod absorbs moisture from both air and soil.
• Continuous conditioning of a large area insures an
ultra-low-resistance ground which is more effective
than a conventional electrode.
• If the conductive salts are running low, the rod
can be recharged with a refill kit.
• These rods are available in vertical and
horizontal configurations.
• They may be used in rocky soils, freezing
climates, dry deserts, or tropical rain forests.
• They provide stable protection for many years.
Disadvantages are:
• Chemicals concentrated around electrodes
will cause corrosion
• Chemicals leach through the soil and dissipate
• Scheduled replacement may be required
• May be prohibited because they may
contaminate the water table
Soil Treatment Alternatives
• Ground enhancement material
Cement-like compound
– Non-corrosive
– Extremely conductive
– Installed around the electrode
– Easy installation
– Permanent
• Installing an EARTHLINK 101 earthling strip is simple:
Dig a trench and lay in the wire.
Pour EARTHLINK 101 conductive cement, using the handy
applicator bag, and shovel in a thin protective layer of soil.
Backfill the remaining soil using a front-end loader
and restore the surface to grade.
UNIT-VI
INTERNAL WIRING
STAGES OF HOUSE WIRING
• There are three stages for house
wiring:
–Underground stage
–Rough stage
–Electrical stage
•From the power company, we get:
•two hot wires
•one neutral wire.
•The two major voltages available in our
homes are:
•115 VAC
•230 VAC
•Most of the receptacles in our homes are 115
VAC.
•Washer, Dryer, Oven, etc. use the 230 VAC
receptacle.
VOLTAGE RECEPTACLES
115 VAC
230 VAC
Ground
wire
Neutral
Hot
Ground
Hot wires
COLOR CODING OF WIRES AND SCREWS
115 VAC
• Wires:
– Hot (red/black wire)
– Neutral (white wire)
– Ground (bare copper wire)
• Screws:
– Brass (for hot wire)
– Silver (for neutral wire)
– Green with green dot (ground
wire)
230 VAC
• Wires:
– Hot (red wire)
– Hot (black wire)
– Ground (bare copper wire)
• Screws:
– Brass (for hot wire)
– Brass (for hot wire)
– Green with green dot (ground
wire)
HOUSEHOLD WIRING FOR ROOMS:
• For rooms:
Within the first 6ft of an entrance into a room, there should be an 120volt
receptacle outlet and then for every other 12ft there should be an outlet.
• For the kitchen:
The outlets should be a minimum of 2ft apart.
• Receptacle connection:
On the side of ground the 2 neutral wires are stripped ½ inch and pushed
in the hole. Make sure to pull on it to check that it does not come out.
Now strip the black wires ¼ inch, push them into the hole opposite of
ground.
14 W gauge for bedrooms, hallways, living rooms, and all ceilings.
Duplex Receptacles:
 Some duplexes have 5 wires going into the receptacle, while others have 3 wires
going into the receptacle.
 If a circuit is a feeder to the other circuits, then it has 5 wires: 2 neutral (white), 2
hot (black/red), 1 ground (bare copper wire). The 5 wires you see are actually
power coming in and coming out.
 If it is the end of a circuit, then it has 3 wires: 1 neutral (white), 1 hot (black/red), 1
ground (bare copper wire)
 Every receptacle holds 15 Amperes of Current. Kitchen appliances have 20 Amperes
of Current and Dryers have 30 Amperes of Current.
 Every wire has an adjacent screw
GFCI
-GFCI: Stands for Ground Fault Circuit Interrupt. This
receptacles is different from conventional
receptacles. In the event of a ground fault, a GFCI will
trip and quickly stop the flow of electricity to prevent
serious injury.
-For kitchens and bathrooms with sinks, GFI
protection receptacles are required for anything
between 6ft from water. Make sure everything is
grounded for safety purposes.
-When does a ground fault occur? It occurs when
electricity passes through a persons body to reach
the ground instead of following its normal path.
-GFCI receptacles protect against circuit overloads,
short circuits, or shocks.
-For GFCI’s, a 12 W gauge is required which is thicker
than the 14 W gauge.
GFCI CONTINUED…
• The GFCI receptacle itself has the Test and Reset buttons.
The reciprocal feeling into the GFCI main no reciprocal has
no Reset/Test buttons, but will indicate GFCI stickers on
them.
not GFCI GFCI
DIMMER
• A single pole (one location) or a 3 way (multiple locations) can be put only
on the incandescent.
• You will see 4 colored wires on the dimmer. Blue, yellow, black and green.
Connecting wires for dimmer:
• Green dimmer Ground leads to Green or
copper wire in wall box.
• Black dimmer lead to Line (hot) wall box
wire removed from old switch.
• Blue Dimmer lead to remaining wall box wire
(Load)
• Cap Yellow dimmer lead with appropriate
size wire nut.
LAMPS
•REGULAR MEDIUM BASE: used in regular fixtures
•MOGUL BASE: is thicker and is used for street lights
•CANDELABRA BASE: is smaller and is used in paddle/ceiling fan
fixtures
*On a ceiling fan which has lights, always use a A15
lamp because the filament is thicker and it will last
longer even though the fan causes vibration*
*G-style lamps are used in bathrooms*
*Fluorescent lamps are used under cabinets and
countertops, and are available only up to a wattage of
32 Watts instead of 40 Watts*
Gang Box
•The Gang Box must be UL listed in approval for
electrical work. Deep Gang Boxes are maximum
of 22.5cubic inches.
•Inside the house : All gang boxes must be UL
approved.
•Outside the house the gangs used must be UL
approved and suitable for dampness/wet
conditions.
•According to Title 24 everything in the home i.e.
Bathroom, Kitchen, underneath the cabinets,
laundry room, outside light should have
incandescent lights.
Low Voltage Wires
Red……Computer-CAT5
White….RG6-TV, SAT, DSL, Cameras
Black…..RG6-””
Blue……Phone-CAT5
You can use red alone but to differentiate
between computer wires and phone wires you
use different colors.
High Voltage Wires
• 14/ 2- 15A :is a 14G wire black, white, and ground used for
lighting wiring bedroom plug switches. anything rated up to
15A.
• 12/ 2- 20A :is a 12G wire, black, white, ground, yellow wire for
identification.
• 12/ 3- 20A :is a 12G wire black (hot) white (neutral), red (hot),
and ground. In this there are
2 hot wires in one wire. If you have two circuits in the same
area then you could use black for one circuit & jump the other
circuits through red wires especially in General appliances.
High Voltage wires Continued
• 10 Gauge/30 A: is Orange in color used for
Dryers or Ovens if under 30 A. it is also used
for Air conditioning if no more than 30A is
required
• 8 Gauge/40/50 A: is a Black wire and is used in
ovens that are over 30 A.
• 6 Gauge/50/60 A: is used only in Air
Conditioners and Ovens that have very high
amperage
ROUGH STAGE
Low voltage enclosure: TV, Telephone, computers, cameras,
speaker DVR, i.e. communication, run one main limit is 2RG6
(TV coax) cat 5- phone line or computer line. When it says TV
run 1RG6 i.e. Black wire.
……………..Phone
P…………………Plug
TV……………….TV
On/Q…………….All 4 wires drop (2cat5 and 2RG6)
High Voltage……Stapled every 4ft 6in
Low Voltage…….Not stapled tightly
1RG6……………TV Only
2RG6……………TV & DVR & HD
Rough Stage Continued…
• RG6-Quad shield: a type of wire that helps to give
a better signal, but not a better picture.
(You could run High Definition signals like
Comcast Internet Company with RG6)
• The wires going into every gang box should be
stapled within 6 inches of the box, on the wood.
• The wires going into Double or Triple boxes,
should be 12 inches away from the box on the
wood.