Electrical Safety

Electricity
- essential and considered as among the basic needs of everybody.
- can be defined as the flow of electrons along a conductor.
*electrons – negatively charged particles distributed in orbits around the
nuclei of atoms.
In an atom, the negative charge of the electrons is neutralized by the
positive charge of particles called protons, so that the atom is electrically
neutral.
If an external force is applied so that the electrons are removed from their
orbit and directed to a given direction, electric current is produced in that
directions.
 Electrical current requires a suitable circuit to provide the energy needed for
lighting, heating, etc. An electrical circuit usually contains a power source and
an electrical load. Suitable conducting materials connects the power source to
the load in order to complete the electrical circuit. These conductors are
covered with a suitable insulating materials to prevent the current from leaking
out.
Conductors – materials that have a relatively large number of free electrons at
room temperature.
Insulators – materials that do not have a large number of free electrons at
room temperature.
Semi- conductors – materials that fall in between the two extremes.
Elements of Electricity:
• Voltage
- A specific measure of potential energy that is always relative between two point.
- measured in terms of volts
• Resistance
- opposition to motion
- measured in Ohms
• Current
- continuous movement of electric charge through the conductors of a circuit.
Often referred on terms of “flow”.
- measure in terms of amperes.
*ampere – is the flow of 6.28 x electrons per second past a given point in a circuit.
Ohm’s Law
- “the current flowing in a circuit is DIRECTLY PROPORTIONAL TO THE VOLTAGE
and INVERSELY PROPORTIONAL TO THE CURRENT.”
Formula for Current Formula for Voltage Formula for Resistance
I= V=I×R R=

Quantity Symbol Unit of Unit Abbreviation

Measurement
Current I Ampere (“Amp”) A
Voltage E or V Volt V
Resistance R Ohm Ω

Ampere – after the Frenchman André-Marie Ampère

Volt – after the Italian Alessandro Volta
Ohm – after the German Georg Simon Ohm
Hazards of Electricity:
• Electric Shock
- common hazard encountered by people involved in the installation,
maintenance, and operation of electrical equipment.
- occurs once the worker’s body becomes part of an electrical circuit when it
comes in contact with a live internal conductor at the point of insulator
breakdown.
- common sources of electric shock are refrigerators and electric fan.
• Burns
• Fire
Common causes of electrical injuries/ accidents:
(a) Touching of live parts
(b) Short circuit
(c) Inadequate guarding
(d) Overloading
(e) Breaking of connections
Factors affecting Electric Shock:
1. Amount of current that flows through the human body.
• Voltage of the circuit. According to Ohms Law, voltage is directly
proportional to the current. A higher voltage means a higher amount of
current.
• Insulating quality
2. The path the current takes through the body affects the degree of injury.
3. Duration of current flow.
4. Type of energy involved. There are two kinds of electrical energy:
• Alternating Current (AC) – the flow of electric charge whose magnitude
and direction changes periodically. This can cause a person to maintain an
involuntary grip on the live metal or conductor and prolong the current
flow.
• Direct current (DC) – the flow of electric charge that does not changes
direction.
5. Body condition. Personality sensitivity to electric shock varies with age, sex,
heart condition etc.
An electrical current passing through the body can cause severe injury or death
by:
• Contracting the chest muscles, resulting in breathing difficulty and death due
to asphyxiation.
• Affecting the central nervous system, resulting in malfunction of vital body
function such as respiration.
• Interference with the normal rhythm of the heart beat, resulting Ventricular
Fibrillation which is defined as “very rapid uncoordinated contractions of the
ventricles of the heart resulting in loss of synchronization between heartbeat
and pulse beat.” once ventricular fibrillation occurs, it will continue and death
will ensue within a few minutes.
 • Electricity may also affect the heart muscle, resulting in severe heart muscle
contraction and cessation of heart action.
• Heat generated when current overcomes tissue resistance may cause
destruction of the body tissues.

Based on the research of Charles F. Dalzeil, professor at the University of

California, the effects of alternating current (60Hz) on the human body are
generally accepted to be as follows: (see table at the next slide)
 Table 8.3 Effect of current on the human body
Current (Ohms) Effect

0 – 1mA No sensation, not felt

1 mA Shock perceptible, reflex action to jump away. No direct
danger from shock but sudden motion may cause accident.
> 3mA Painful shock
6 mA Let go current for women
9 mA Let go current for men
>10mA Local muscle contractions, sufficient to cause freezing to the
circuit for 2.5% of the population
>15mA Local muscle contractions, sufficient to cause “freezing” to
the circuit for 50% of the population
>30mA Breathing difficulty; can cause unconsciousness
50 – 100 mA Possible ventricular fibrillation of the heart
100 – 200mA Certain ventricular fibrillation of the heart
> 200mA Severe burns and muscular contractions; heart more apt to
stop than fibrillate
> 1A Irreparable damage to body tissue
• Let go Current – the maximum current that a person can tolerate when
holding a conductor and can still be free himself/herself by muscular
stimulation
Four main types of injuries by electric currents – electrocution (fatal),
electric shock, burns, and falls:
• direct contact with the electrical energy.
• When the electricity arcs (jumps) through a gas (such as air) to a person who
is grounded (that would provide an alternative route to the ground for the
electricity).
• Thermal burns including flash burns from heat generated by an electric arc ,
and flame burns from materials that catch fire from heating or ignition by
electric currents. High voltage contact burns can burn internal tissues while
leaving only very small injuries on the outside of the skin.
• Muscle contractions, or a startle reaction can cause a person to fall from a
ladder, scaffold or aerial bucket. The fall can cause serious injuries.
Electric Prevention:
(a) Use of Grounding System
Grounding or Earthing is an means of absorbing any leakage current and
making it flow directly to earth by using an electrical conductor.
Two types of Grounding:
(1) System Grounding – means grounding the neutral point iron terminal of
electrical circuits on power transformer of electrical system
(2) Equipment Grounding – grounding of a non-charged metal part of
electrical equipment.
(b) Use Double Insulating materials
(c) Use Appropriate Disconnecting Means
(1) Fuse - a strip of metal that of metal that melts at a pre-determined value
of current flow, and therefore cuts off the current to that circuit.
 Circuit Breaker
FUSE Earth Leakage
Circuit Breaker
 (2) Circuit Breaker – has several advantages for excess current circuit
protection. The principle of the operation is that excess current flow is
detected electromagnetically and the mechanism of the breaker automatically
trips and cuts off electric supply to the circuit it protects.
(3) Earth Leakage Circuit Breaker – detect both over-current and earth
leakage currents and thereby give very good circuit protection.
(d) Proper Maintenance of Portable Breaker

Causes of Electrical Fire:

• Arcs – produced when an electric circuit carrying a current is interrupted,
either intentionally – by a knife switch or accidentally – where a contact at a
terminal becomes loose.
• Sparks
• Overheating
ARCS SPARKS
Hazardous Locations
- Are areas where explosive or flammable gases or vapor, combustible dust, or
ignitable fibers are present or likely to be present. Such materials can ignite
as a result of electrical causes only if two conditions co-exist:
1. The proportion of the flammable substance to oxygen must permit
ignition and the mixture must be present in a sufficient quantity to
provide an ignitable atmosphere in the vicinity of electrical equipment.
2. An electric arc, flame escaping from an ignited substance in an
enclosure, heat from an electric heater or their source must be present
at a temperature equal to or greater than the ignition point of the
flammable mixture.
Classification of Hazardous Locations:
Class I - locations where flammable gases or vapors are
present or likely to be present.
Class II - applies to combustible dusts.
Class III - locations are those where easily ignitable dust such
as textile fibers are present but not likely to be suspended in the air
in sufficient concentration to produce an easily ignitable
atmosphere.

Explosion Proof Apparatus – a device enclosed in a case that is capable of:

• Withstanding an explosion of a specified gas or vapor that may occur within it.
• Preventing the ignition of a specified gas or vapor outside the enclosure that
may be caused by sparks, flashes or explosion of the gas or vapor inside the
apparatus.
Sample Checklist for the Basic Electrical Safety:
Inspect Cords and Plugs
• Check power cords and plugs daily. Discard if worn or damaged. Have any cord that
feels more than comfortably warm checked by an electrician.

Eliminate Octopus Connection

• Do not plug several power cords into one outlet.
• Pull the plug not the cord.
• Do not disconnect power supply by pulling or jerking the cord from the outlet.
Pulling the cord causes wear and may cause a shock.

Never Break OFF the Third Prong on a Plug

• Replace broken 3-prong plugs and make sure the third prong is properply grounded.
Never Use Extension Cords as Permanent Wiring
• Use extension cords only to temporary supply to an area that does not have
a power outlet.
• Keep power cords away from heat, water and oil. They can damage the
insulation and cause a shock.
• Do not allow vehicles to pass over unprotected power cords. Cords should
be put in conduit or protected by placing planks alongside them.