Basic electricity

Sreeraj S R
Electrotherapy
Basic Electricity

Sreeraj S R
What is electrotherapy?
Medical therapy using electric currents. Also
called electrotherapeutics.
Electrotherapy, also electro physical agents
(EPA) are any forms of treatment or
assessment conducted using an electro
physical agent which can be applied externally
to the human body.
http://www.thefreedictionary.com/electrotherapy
Robertson V, Ward A, Low J, Reed A. Electrotherapy Explained. 4th edition. Elsevier; 2006. p. 2

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Atom
http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/static_elec/staticrev1.shtml

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Atom
Electrons fill the lowest
energy shells
Atoms tend to have their
outer shell full
They may gain or loose
electron to achieve this.
If the atom gains an
electron it is negative ion.
(Cl-)
If the atom loses an
electron it is positive ion.
(Na+)
Forster A, Palastanga N. Clayton’s Electotherapy, Theory ans Practic. 9th Ed. W B Saunders; 2006. p 2
http://198.185.178.104/iss/electricity/pages/b11.xml

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Atom
Atoms can have an electrical charge, positive or negative.
This happens when an atom gains or loses electrons.
The number of protons never changes in an atom.
More electrons means a negative charge and fewer means a
positive charge.
Once an atom has an electrical charge it is called an ion.
In an ion the atomic number and atomic mass do not change
from the original.
If an atom were to gain or lose neutrons it becomes an
isotope.
http://www.universetoday.com/56747/atom-structure/#ixzz2dT7JQkrm
http://revisionworld.co.uk/quick-revise/5133

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Chemical bond
A chemical bond is an attraction between atoms that
allows the formation of chemical substances that
contain two or more atoms.
The bond is caused by the electrostatic force of
attraction between opposite charges, between
electrons and nuclei.
The number of electrons in the outer shell of an atom
has the effect on the reactions of that atom with others.
Inert gases like argon, krypton have complete outer
shell.
Reactive gases are those elements are looking to
complete their outer shell so they are reactive.
http://en.wikipedia.org/wiki/Chemical_bond

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Compounds
A compound is a substance formed by the union of two
or more elements
They can be separated into simpler substances
by chemical reactions.
They have a unique and defined chemical structure;
They consist of a fixed ratio of atoms
Chemical compounds can be;
molecular compounds held together by covalent
bonds,
salts held together by ionic bonds/ electrovalent,
http://en.wikipedia.org/wiki/Chemical_compound

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Covalent Bonds
A form of chemical bonding
between two atoms which is
characterized by the sharing of
pairs of electrons between atoms.
A covalent bond is formed
between two non-metals that
have similar electro negativities.
Neither atom is "strong" enough
to attract electrons from the other.
For stabilization, they share their
electrons from outer molecular
orbit with others.
http://www.diffen.com/difference/Covalent_Bonds_vs_Ionic_Bonds
http://facstaff.gpc.edu/~pgore/PhysicalScience/Naming-chemical-compounds.html

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Electrovalent Bonds
Also known as Ionic bond.
formed from the electrostatic
attraction between oppositely
charged ions in a chemical
compound.
occur mainly between a metallic
and a non metallic atom.
Non-metals (-ve ion) are
"stronger" than the metal (+ve
ion) and can get electrons very
easily from the metal.
These two opposite ions attract
each other and form the ionic
bond.
http://www.diffen.com/difference/Covalent_Bonds_vs_Ionic_Bonds
http://facstaff.gpc.edu/~pgore/PhysicalScience/Naming-chemical-compounds.html

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Covalent Bonds vs. Electrovalent Bonds
Covalent Bonds.. Electrovalent Bonds..
are formed by mutual sharing of electrons are formed by complete transfer of
electrons
are made up of molecules. are made up of ions.
are usually liquids or gases. are hard, crystalline solids
are insoluble in polar solvents like water. are usually soluble in water.
are soluble in non-polar solvents like
benzene or carbon tetrachloride
insoluble in non-polar solvents like CI4.
generally have low melting and boiling
points.
generally have high melting and boiling
points
are bad conductors of electricity. are good conductors of electricity in the
molten state and in aqueous solutions
but insulators in the solid state.
http://www.publishyourarticles.net/knowledge-hub/science/what-is-the-difference-between-electrovalent-and-
covalent-compounds.html

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Static Electricity?
A stationary electrical
charge that is built up on
the surface of a material
After being rubbed, a
plastic ruler can attract
paper scraps.
Ruler carries electric
charge.
It exerts electric force on
paper
The interaction between
static electric charges is
called electrostatics.

Sreeraj S R
Insulators and conductors
In a conductor, electric current can flow freely,
in an insulator it cannot.
"Conductor" implies that the outer electrons of
the atoms are loosely bound and free to move
through the material.
Most atoms hold on to their electrons tightly
and are insulators.

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Insulators: materials that do NOT allow
electrons to flow through them easily.
Insulators can be easily charged by friction as the extra
electrons gained CANNOT easily escape.
Static Electricity ppt

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Conductors: materials that allow electrons to flow
through them easily.
Conductors CANNOT be easily charged by friction as
the extra electrons gained can easily escape.

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+
+ + +
+
metal can - -
-
-
-
----- --
induced
charges attraction
repulsion
Induction
• The production of a charge in
an uncharged body by
bringing a charged object
close to it.
When negatively charged rod is
put near a metal can...
• electrons of the can are
pushed away from the rod.
• top of the can: positive
• buttom of the can: negative
• So there is attraction >
repulsion

Sreeraj S R
Induction
----- --
paper +
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
attraction
repulsion
• Similarly, when
charged rod is close
to paper scrap...
• molecules of paper
align
• attraction between the
rod and + charge
• repulsion between the
rod and - charge

Sreeraj S R
Electric Fields
They are nothing but a way of pictorially mapping the electric field around
a configuration of charges.
General Properties of Electric Lines of Force
The lines of force or field lines
1. start from positive charges and end at negative charges. In the case of
a single charge, they may start or end at infinity.
2. two field lines can never intersect each other.
3. contract longitudinally.
4. exert lateral pressure on one another.
5. are perpendicular to the surface of a charged conductor.
6. do not pass though the conductor.
http://www.tutorvista.com/content/physics/physics-iv/electric-charges/electric-field-lines.php

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Electric Fields
If it is a positively charged body, then the
electric lines of force are directed away from
the body.
If the body is negatively charged, then the
lines of force are directed towards the body.

Sreeraj S R
Electric Fields
When two positively charged bodies are
involved, the electric lines of force gives a
vivid picture of mutual repulsion.
In the case of two equal and opposite charges,
the lines of force clearly shows mutual
attraction, the lines move from +ve to -ve.

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Electrical Current
http://www.howequipmentworks.com/physics/electricity/basic_electricity/basic_electricity.html

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Electrical Current
Current
Voltage
Resistance
http://www.reprise.com/host/electricity/voltage.asp

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Current
amount of electric
charge passing a point in
an electric circuit per unit
time
Current is measured in
units called amperes.
6.241 × 1018 electrons, or
one coulomb per second.
The quantity of electricity
is measured in coulombs.
http://en.wikipedia.org/wiki/Ampere

Sreeraj S R
In medical electricity the unit of current is in
milliamperes i.e. 1/1000 of an ampere

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Voltage
potential difference
across a conductor when
a current of one ampere
dissipates one watt of
power.
The unit of
measurement for
potential difference is
"volt".

Sreeraj S R
Resistance
electrical resistance is
something that “resists” the
flow of electrons/current.
Electrical resistance is
measured in Ohms ( ).
Most circuits have more
than one component, called
a resistor
A measure of this limit on
charge flow is
called resistance

Sreeraj S R
Resistance; Ohm's law
Ohm's law states that the
electrical current (I)
flowing in a circuit is
proportional to the voltage
(V) and inversely
proportional to the
resistance (R).
I = V / R
Where:
I = Electrical Current (Amperes)
V = Voltage (Voltage)
R = Resistance (Ohms)
http://inspectapedia.com/electric/ElectricalDefinitions.htm#Resistance
http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/currentflow.htm

Sreeraj S R
Resistance; Ohm's law
http://www.howequipmentworks.com/physics/electricity/basic_electricity/basic_electricity.html#ohm_law

Sreeraj S R
Resistance
The simplest combinations
of resistors are the
a) series and
b) parallel
http://cnx.org/content/m42356/latest/?collection=col11406/latest

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Series Circuits
A series circuit is a circuit
in which resistors are
arranged in a chain
so the current has only
one path to take.
equivalent resistance of
resistors in series :
R = R1 + R2 + R3 + ...
The current is the same
through each resistor but
Voltage changes on each
resistor
http://physics.bu.edu/py106/notes/Circuits.html
http://cie-wc.edu/Series-and-Parallel-Circuits-4-11-11.pdf

Sreeraj S R
Parallel circuits
In a parallel circuit the
resistors are arranged with
their heads connected
together, and their tails
connected together.
equivalent resistance of
resistors in parallel :
1/R=1/R1+1/R2+1/R3.....
The current in a parallel
circuit breaks up but
The voltage across each
resistor in parallel is the
same.
1
0.2+0.0714+0.0476+0.04+0.01 = 2.7
http://cie-wc.edu/Series-and-Parallel-Circuits-4-11-11.pdf

Sreeraj S R
Electrical Watts
Watts is a measure of the amount of electricity being
used - a rate of electrical power consumption.
power (Watts) = current (amps) x potential
difference (volts)
For a current of 5 A and the potential difference of 12
V, the power is 5 × 12 = 60 W.
This means that 60 J of energy is transferred per
second.
http://inspectapedia.com/electric/ElectricalDefinitions.htm#Watts
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/electricity/mainselectrev4.shtml

Sreeraj S R
Joule’s law
When a current passes through a conductor
some of its energy is converted to thermal
energy.
Joule’s law states that the amount of heat
produced in a conductor is proportional to the
square of the current in amperes (I2), the
resistance in ohms (R) and the time in seconds
(t) for which the current flows. i.e.
Q = I2 Rt

Sreeraj S R
Basic Electrical Components

Sreeraj S R
Resistor
A resistor is an electrical
component that limits or
regulates the flow of
electrical current in an
electronic circuit.
http://searchcio-midmarket.techtarget.com/definition/resistor
http://www.mikroe.com/old/books/keu/01.htm

Sreeraj S R
Transformers
A transformer is an electrical apparatus
designed to convert alternating current from
one voltage to another.
The functions of Transformers are;
To alter the voltage of an alternating
current
To render the current earth free
http://www.acmepowerdist.com/pdf/Page_6-16.pdf

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Transformers, Working
Transformer works on
the principle of mutual
induction of two coils.
When current in the
primary coil is changed,
the flux linked to the
secondary coil also
changes.
Consequently an EMF
is induced in the
secondary coil.
Upadhyay D . Electrical & Electronics Engineering. Hindustan college of Science & Technology. Ppt presentation

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Transformers; Construction
The core, which provides a
path for the magnetic lines of
flux.
The primary winding, which
receives energy from the AC
source.
The secondary winding,
which receives energy from
the primary winding and
delivers it to the load.
The enclosure, which protects
the above components from
dirt, moisture, and mechanical
damage.
http://www.navymars.org/national/training/nmo_courses/NMO2/module2/14174_ch5.pdf
http://www.emt-india.net/process/power_plants/Transformers.htm

Sreeraj S R
Transformers; Construction
Mainly Transformers have two
types of construction….
CORE type: the primary
and secondary windings are
placed on each side of the
core.
The core type has two limbs
SHELL type: the LV & HV
windings are sandwiched
between each other.
shell type has three limbs.

Sreeraj S R
Transformers, Types
Step-up transformer Step-down transformer
http://keywon.com/wiki/index.php?title=AC_Circuits

Sreeraj S R
Transformers, Configurations
Static transformer
Variable transformer
Auto transformer
http://keywon.com/wiki/index.php?title=AC_Circuits
http://www.cybermike.net/reference/liec_book/AC/AC_9.html
http://en.wikipedia.org/wiki/File:Tapped_autotransformer.svg

Sreeraj S R
Transformers, in Earthing
Using power without an isolating
transformer: Touching the live terminal
will result in a shock as the body
completes a circuit between live and
earth.
Using power with an isolating
transformer: Bridging between either
terminal and ground is safe because there
is no circuit through which the current
can flow.
http://www.soundonsound.com/sos/nov06/articles/crosstalk_1106.htm

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Capacitor
What is Capacitance?
Capacitance is the ability of a device to store
electrical energy in an electrostatic field.
Or the ability of a component to store an
electrical charge.
The Symbol for Capacitance is “C”
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&ved=0CGIQFjAH&url=http%3A%2F%2Fwww.
hamptonhigh.ca%2Fhaas%2Fdocuments%2Fintro%2FCapacitors.ppt&ei=RgYuUpjYNcLWrQfb9IGoDw&usg=AFQjCNFzJkiINpxX
A1epNOtoJ8FhQcaO8g&sig2=fUpX1eYhXN5TWWr11HrtGg

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Capacitor
Capacitance is measured in Farads (F).
The Farad is too large for ordinary use so
typically the Microfarad of the Pico farad are
used.
µF = Microfarad
pF = Picofarad
1 µµµµF = 0.000,001F
1 pF = 0.000,000,000,001F
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&ved=0CGIQFjAH&url=http%3A%2F%2Fwww.
hamptonhigh.ca%2Fhaas%2Fdocuments%2Fintro%2FCapacitors.ppt&ei=RgYuUpjYNcLWrQfb9IGoDw&usg=AFQjCNFzJkiINpxX
A1epNOtoJ8FhQcaO8g&sig2=fUpX1eYhXN5TWWr11HrtGg

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Capacitor
Also referred to as
a Condenser
It is a device for storing
electric charge.
Capacitors consist of
two conducting surfaces
separated by an
insulator.
http://www.electronics-tutorials.ws/capacitor/cap_1.html

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Capacitors,working
When a capacitor is connected to a
voltage source current will flow until
the capacitor is fully charged.
The capacitor is charged with an
excess of electrons on one plate (-
charge) and a deficiency of electrons
on the other plate (+ charge)
A capacitor discharges when the
accumulated charge is allowed to
flow off the plates.
The time taken for this discharge
depends upon
1. Capacitance of condenser
2. Resistance of pathway
3. Quantity of electricity

Sreeraj S R
Capacitors, electric field
The EF between the
plates of a charged
capacitor tend to take
the shortest route.
They repel one another
They rarely travel on
straight line
http://commons.wikimedia.org/wiki/File:VFPt_capacitor.svg

Sreeraj S R
Capacitors, oscillator circuit
An oscillatory circuit is
that of a condenser and
an induction coil in low
ohmic resistance.
Forster A, Palastanga N. Clayton’s Electotherapy, Theory ans Practic. 9th Ed. W B Saunders; 2006. p 35-36

Sreeraj S R
Capacitors, oscillator circuit
http://en.wikipedia.org/wiki/File:Tuned_circuit_animation_3.gif

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Capacitors, Types
Fixed Capacitors
the capacitance cannot be changed.
Variable Capacitors
the capacitance can be changed.

Sreeraj S R
Capacitors, Types
Fixed Capacitors
Electrolytic
Electrostatic
Mica
Ceramic
paper

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Capacitors, Types
Variable Capacitors
air capacitors
trimmers

Sreeraj S R
Thermionic valves
These are devices which
allow electron flow in
one direction only and
working using heat.
The cathode (filament)
heated o produce space
charge of electrons.
The anode (plate)
attracts electrons across
the valve.

Sreeraj S R
Thermionic valves
Triode valve
It is possible, using an
external circuit to make
the grid
– ve: repel electron to
stop the flow
+ ve: allows electron
flow through valve
Neutral: grid will not
effect electron flow

Sreeraj S R
Thermionic valves
Uses:
Rectification: as current flows in one direction
it is possible to convert an AC to DC
Amplifier: triode valve can be used as
electronic amplifier
Switch: triode valve can be used to braek the
circuit.

Sreeraj S R
Semiconductors
They are usually metals
with the addition of
impurities have electrons
free to conduct current
n – type with excess of
electrons
p – type with deficiency of
electrons so + ve ‘holes’
If a p- and n- type
semiconductors are fused
together current can only
flow in n to p direction
i.e. it acts as a valve
Forster A, Palastanga N. Clayton’s Electotherapy, Theory ans Practic. 9th Ed. W B Saunders; 2006. p37

Sreeraj S R
Transistors
Device that uses a small
amount of current to control
a large amount of current
(Current Amplifier).
They utilize a sandwich of
p- and n- type
semiconductor materials.
Electron enters at emitter
current amplified and passed
across through base
Electron leaves form
collector

Sreeraj S R
Rheostat
Devices used to regulate current by altering
either the resistance of the circuit or
the potential in part of the circuit
Forster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 39-40

Sreeraj S R
Rheostat
Construction
It consists of a coil of high
resistance wire wound onto
an insulating block with
each turn insulated from
adjacent turns.
Contact is made via a strip
from which insulation is
removed.
The contact is mounted on
a sliding bar or rotation
knob.

Sreeraj S R
Rheostat
Variable or series rheostat
If all the coils of wire in
rheostat are included in
the circuit resistance is
maximum and current
lowest
Used in regulating heat in
apparatuses like paraffin
wax baths

Sreeraj S R
Rheostat
Potentiometer or shunt
rheostat
Wired across a source of
potential difference in
parallel.
According to ohm's law
greater the PD across the a
resistance the greater the
current produced.
When B at A no PD, so no
current
When B at C maximum PD
as in A
A current regulating
mechanism

Sreeraj S R
General structure of LF generators
Low J, Reed A. Electrotherapy Explained, Principles and practice. 2 edition. Page 19

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Mains supply
Current for this is
produced by dynamos
(electrical generator) at
power stations.
An EMF is induced by
the movement of a
conductor and two
magnetic field in
relation to each other.
Dynamos can produce
either AC or DC
http://aaenvironment.com/Electricity.htm

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Mains supply
Advantages of AC
A greater voltage can be produced
Possible to alter voltage with static
transformers
So suitable for long distance transmission

Sreeraj S R
Mains supply, The grid system
Residential power supplied in India is two wire
220 volts, permitted variation 6%, and maximum
load 40 amperes. Frequency 50 Hz.
A three phase current is generated.
i.e. three coils of dynamo generate three separate
current.
Distribution of current via three live cables with
a common neutral cable.
These four cables carry current across the country.
http://en.wikipedia.org/wiki/Mains_electricity_by_country

Sreeraj S R
Mains supply
http://en.wikipedia.org/wiki/File:Electricity_grid_simple-_North_America.svg

Sreeraj S R
Mains supply, wiring in house
Distribution to customer is by one live wire
and one neutral wire
It passes through main fuses, meter, main
switch and to various circuits in parallel.
The light circuits have 5 ampere fuses for
each 4 to 6 points
The power circuit with stronger wiring with
15 ampere fuse for each point.
Forster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 43

Sreeraj S R
Fuse
It is designed to be a
weak point in a circuit
which ‘blows’ if a
current of too great
intensity is passed.
This causes the circuit
to break
It consists of a wire of
low melting point.
It is an safety feature.
Metal cap
To mains live wire
To neutral wire
Glass tube
Silver fuse wire
Metal cap

Sreeraj S R
Fuse
In Physiotherapy department a Fuse is an
essential safety feature.
They are included in the
department wiring and
electrotherapeutic equipments
If a fuse blows, the apparatus which causes the
damage should be disconnected and the main
supply switch off.

Sreeraj S R
Power plug
Three pin plug most common

Sreeraj S R
Earthing of apparatus
Precaution against earth shock
Earthing the device casing with a low
resistance wire.
In the event of device casing comes in contact
with exposed live wire the operator can receive
a shock.
However earthing the casing causes the current
to leak through and causes the fuse to blow.

Sreeraj S R
Electric shock
A shock is a painful stimulation of sensory nerves
caused by a sudden flow, cessation or variation in
the current passing through the body.
Severity of shock depends on
the magnitude of the current and
The path taken by the current.
Path taken through head, neck, heart or whole
body might prove fatal.
Shocks are more sever with AC than DC.

Sreeraj S R
Electric shock, effects
A minor shock leads to fright and distress.
A severe shock can lead to;
Fall in BP
Loss of consciousness
Respiratory failure: signs of cessation of
respiration, cyanosis
Cardiac arrest: signs of absent/abnormal
breathing, absence of pulse and fully dilated
pupils

Sreeraj S R
Electric shock, treatment
Following minor shock
Disconnect the victim from source.
Switch off current.
reassure the patient and allow to rest.
Give cold water to drink. (avoid hot water as it
can cause vasodilation and sweating leading to
fall in BP)

Sreeraj S R
Electric shock, treatment
Following severe shock
Victim is laid flat and allow easy breathing
Loosen tight clothing
Provide adequate ventilation
If the patient is unconscious summon MO.
If cessation of breathing give mouth to mouth,
mouth to nose or O2 by bag and mask
In the event of cardiac arrest cardiac message
must be added along with above.
Call for medical help immediately.

Sreeraj S R
Electric shock, causes
Sudden increase in current during treatment
due to:
Machine switched don with controls up.
Sudden appearance of pulsed current with the
intensity high
Patient touching the machine

Sreeraj S R
Electric shock, precautions
The apparatus and the connections should be
tested before use
Controls should beat zero before switching on
Provide adequate warm up for equipment if
needed
Instruct the patient not to touch the apparatus
Service the apparatus regularly
Singh J. Text book of Electrotherapy. 2 edition. Jaypee. 2012. p 64

Sreeraj S R
Earth shock
When a shock is due to a connection between the live
wire or earth it is known as an earth shock.
Connection to live wire can occur when
Wire is not properly insulated.
The live wire is not disconnected when the switch
is put on neutral wire
Live wire touching metal casing
Live wire is touched to wet thing
Connection to live wire can occur when
Touching any conductor connected to earth
Metal casing on apparatus

Sreeraj S R
Earth shock, precautions
Proper arrangement of physiotherapy
department with insulating materials
Proper flooring with insulating materials and
kept dry
Patient should not touch the apparatus
Metal casing of all aparatus shold be
connected to earth
Use wooden furnishings

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