3. Secondary Hazards
Person falling from height
Dropping of tools & objects
Health hazards due to release of toxic gas &
production of UV rays
Psychological effects
Emotionally anxious
Distracted
More prone to accidents
4. Electric Shock
It is sudden & accidental stimulation of the body’s nervous system by
electric current. It is the result of passage of electric current through the
human body
5. Severity Of Shock Depends -
Duration of flow
Amount of current
Path of flow of current
Type of energy
6. Body Resistance
Body area resistance (ohms)
Dry skin 1,00,000 to 6,00,000
Wet skin 1000
Internal body -
Hand foot 400 to 600
Ear to ear (about) 100
7. • I = V / R
= 230 / 100000 A (Dry Condition)
= 0.0023 A
= 2.3 mA
• I = 230 / 5000 (Wet Condition)
= 0.046 A
= 46 mA
POWER
SOURCE
Person
in touch
with
live wire
P
N
8. Effect Of Electric Current On Human Body
Contact current Level, rms 50 Hz
LEVEL EFFECT ON HUMAN CHILDREN WOMEN MAN
1 Shock, Let – go border line of painful
shock, Muscles still under control
<= 4 mA
>= 5 mA
<= 6 mA
>= 7 mA
<= 10 mA
>= 10 mA
2 Muscle control affected 6 mA 10 mA 15 mA
3 Breathing difficulties start 10 mA 15 mA 20 mA
4 Respiratory Titany & breathing
difficulties
10 mA 15 mA 20 mA
5 Fibrillation of muscles with 3 sec.
Fibrillation current. Muscle control
affected. Muscle contraction. Breathing
difficulties. Respiratory titany
30 mA 50 mA 80 mA
6 Severe shock & possible death due to
rapid, uncoordinated series of
contraction of heart muscles causing
irregular heart beat & possible death
40 mA
> 3 sec.
50 mA
> 3 sec.
60 mA
> 3 sec.
7 Severe burns, muscular contractions,
stoppage of heart. Death certain
50 mA 80 mA
10 sec.
100 mA
9. How Shock Occurs
By simultaneously touching the phase and neutral conductor thus
completing the circuit through his body
R
Y
B
N
LOAD HAVING
METALLIC BODY
ALTERNATOR
10. 2. By touching the phase conductor and standing on the ground
N
ELEC. EQPT.HAVING
METALLIC BODY
ALTERNATOR
R
Y
B
11. 3. By touching a metallic part that has become live by itself being in contact
with an energised wire
N
ELEC. EQPT.HAVING
METALLIC BODY
ALTERNATOR
R
Y
B
13. Isolation
All electrical equipment should be isolated from accidental contact &
approach by unauthorised men. Providing barrier
Panel boards, generators, large motors, batteries should be enclosed
Low & medium voltage OH lines should be kept 19” above the ground
14. Isolation Switches
The switches should be connected in phase only
The switches should be easy and free to operate
Body of the metallic switches should be earthed
Every DB should be provided with a switch
It is advisable to keep switch as near as possible to the work-
place
P
N
POWER
SOURCE
If switch is connected in neutral, the person, who repairs
the equipment, could get shock though the supply is cut
using the switch.
15. Isolation Transformer
Power can be tapped from isolation transformer
for the power tools and for testing electric
Equipment (In working condition)
Avoids shock between earth and phase
SINGLE PHASE
TRANSFORMER
16. Low Voltage
•To provide equipment with low voltage that dangerous effects
are considerably reduces. This low or safe voltage is 24V. This
voltage is accepted as being sufficiently low to avoid injury to
person coming directly into contact with it.
•For electrically driven portable equipment like, grinding
machines, drilling machines, vibrator (used in concreting
works), etc. the 230V centre- tapped transformer system can be
used.
•By earthing the mid point of a single phase transformer, the
line to earth voltages are reduced to 115V while the full
supply(230) is available to the apparatus.
CENTRE TAPPED
TRANSFORMER
230V
115V
17. Double Insulation
•In addition to the normal insulation required for
functioning of the equipment, a second layer of
insulation known as protective insulation is
interposed between functional insulation & any
accessible metal parts of appliances.
•Double insulated power tools have non-metallic
body
•Need not be earthed (two point plug is sufficient)
Insulation
Functional Protective
19. Check in General for
Neutral earthing (In case of X-mer or DG)
Protective shed
Body earthing
Earth pit for body earthing
Earth resistance
Fuses
Loose connection of cable
Housekeeping
Fire extinguisher and type
21. PLUG TOPS
HAND TOOL
METALLIC BODY
• PLUG TOPS SHOULD BE USED TO AVOID SHOCK
DANGER.
• THREE POINT PLUG IN CASE OF METALLIC BODY
HAND TOOLS AND TWO POINT PLUG IN CASE OF
DOUBLE INSULATED HAND TOOLS.
22. Earthing
NEUTRAL EARTHING EQUIPMENT EARTHING
Connecting to earth the non
current carrying metal parts of
equipment is Equipment earthing
The potential of earthed body does
not reach to dangerously high
value since it is connected to earth
Earth fault current flow through
the earthing and may readily cause
operation of fuse or an earth fault
relay
Intentional connection of
neutral point to earth is Neutral
or System Earthing
It is universal practice to have a
neutral earthing at each voltage
level
The voltage does not reach to a
dangerous high value. Earth
fault protection becomes easy
23. Earthing Scheme for Construction Power Facilities
MAIN DB
EARTH ELECTRODE
50 X 6 G.I. FLAT
CLIENTS
SUB - DB
PIPE EARTH PIPE EARTH
DRG NO. STD/CONP/002
FDB
PIPE EARTH PIPE EARTH
EARTH CONTINUITY CONDUCTOR
(SEPARATE OR AS THIRD / FOURTH CORE
25 X 3 G.I. FLAT
NO. 8 SWG G.I. WIRE
INTERCONNECTION WITH
CLIENTS EARTH GRID
EARTH ELECTRODE
DRG NO. STD/GRD/021
24. Details of Earthing Station With GI Pipe
x x
SECTION ‘X’ - ‘X’
12 HOLE
STRIP
200
EARTH LEAD
EARTH LEAD
4”
GROUND LEVEL
BRICK IN LIME
OR CEMENT
FUNNEL
229
338
229
305
RCC SLAB (WITH IDENTIFICATION
MARKING)
CHARCOAL OR COKE IN
POWDER FORM MIXED
WITH SALT & CLAY
38 NB
GI PIPE
2700mm LONG
2500 (MIN.)
150 150
NOTE: SUFFICIENT WATER TO BE
POURED INTO SUMP TO KEEP
SOIL SURROUNDING EARTH PIPE
PERMANENTALY MOIST
DRG
NO.
STD/GRD/024
25. Current Limitation
Safety is assured by purposely limiting the shock intensity from a device
(ELCB) to a value known to be reasonable safe
Circuit breakers & fuses will open under comparatively large current which
is fatal to human beings. ELCB's are sensitive to small currents & hence
isolate the supply within very short time
26. ELCB
(EARTH LEAKAGE CIRCUIT BREAKER)
For portable power tools power supply is taken through ELCB
Saves persons from electric shock
It opens the circuit when it senses leakage current from
earth.
ELCB
SWITCH
BOX
POWER
SUPPLY
Person in
touch with
faulty eqpt.
Having
elec.
Charges on
it”s body
27. Earth Leakage Circuit Breaker
For portable power tools power supply should
be taken through ELCB
ELCB’s OF 30 mA sensitivity to be used
See the current rating of the ELCB. It is
normally 63 A. Depending on that the number
of ELCB’s to be determined. It is uneconomical
to go for large no. of ELCB for few connections
Test the ELCB weekly and record it.
28. Cable Routing
All electrical cables should be run either overhead (7 feet) or
underground
Cable routing layout map to be prepared so that it does not cause
tripping hazards
Welding and power cables not to be overlapped
29. Cables
Single phase supply
◦ Phase - red
◦ Neutral - black
◦ Earth - green
Three phase supply
◦ Phases
◦ Red
◦ Yellow
◦ Blue
◦ Neutral - black
30. Cable Joints
Staggered joints
◦ Joints are not to be overlapped
◦ One primary insulation and an overall secondary insulation is to be done
◦ Proper insulation tape are to be used
Jointing kit
CABLE 1
CABLE 2
3/4” 3/4” 3/4” 3/4”
32. Hand Lamps
Only 24V hand lamps are to be used
Hand lamps are to be enclosed by glass surrounded by metal wire mesh
Hand lamps used for confined space work should be of all insulated
type with no joints
33. Causes of Electric fire
Selection of improper/substandard equipment and materials.
Electrical installation not in accordance with statutory
regulations.
Overloading of equipment.
Maintenance negligence.
Failure of insulation level.
Damage due to rodents, termites and pests.
Lightning.
Water seepage.
34. Maintenance negligence
i) Temporary electrical connection
ii) Bad switch contacts
iii) Improper substitution of electrical equipment and
materials
iv) Allowing equipment for regular usage after repairs
without complete check-up
v) Non-protection against mechanical damages.
35. Failure of insulation level
Insulation failure occur due to following various reasons:-
i) Reduction in voltage with standing capacity because of
excess temperature.
ii) Deterioration in mechanical properties due to excess
temperature where the insulation is mechanically vulnerable
and the mechanical failure leading to electrical failure of the
insulation.
iii) Aging causes deterioration of the insulation.
iv) Sub-standard material are more prone to insulation
failure.
36. Extinguishing Electrical Fire
There are two methods to combat the fires of electrical origin or
involving electrical equipment:
With the use of hand appliances
CO2 type fire extinguisher
With the use of fixed installations
Automatic DCP type extinguisher installation
Multifire system installation
Halon/CO2 Flooding system installation
38. WELDING
1. The body of the welding machine should be earthed.
2. The terminals of the welding cables should be provided with lugs and kept
tight.
3. The joints in the cables should be made with ferrules, kept tight and well-
insulated with heat-resistant tape.
4. The cable should be free from joints atleast for a length of three metres
from electrode holder to avoid shock hazard.
5. Other electrical cables should not be kept laid with welding cables, to
avoid insulation damage.
39. 6. For the return lead only proper cable should be used. Using rods, angles,
channels, etc. should be avoided.
7. The carbon particles, settled between the terminals of the starter, should
be removed periodically.
8. In case of oil-cooled welding transformer the vent hole should be kept
open always so that no oil vapour gets accumulated inside. Accumulation of
oil vapour could cause blasting of the transformer. Di-electric capacity of the
transformer oil should be periodically checked and when it exceeds it’s limit,
the oil should be changed.
WELDING
40. Electric Burns
Chief causes are pushing of fuses inside switches, explosion due to
short circuit inside switches, pressing of cables of portable
machines & damage to hand lamp cables
Devices have been provided to protect injuries due to above
causes. High rupturable capacity fuses are enclosed type. Covers
are sealed and mechanically interlocked
1. BURNS FROM ELECTRIC FLASH &
2. BURNS FROM ELECTRIC HEAT
41. Electric Flash
It is the result of the breaking of circuit of electric current
Higher the current, slower the rate of separation of parts, the greater is
the flash
It is the result of arcing
Being a known hazard sufficient preventive measures are taken to guard
against it like magnetic blow out coil & arc chutes
Electric flash generally affect the eyes, if a person sees it with his naked
eyes. Personal protective equipment has to be used
42. Check
DG
Control Panel
Changeover Switch
Main SDB / SDB
Fuse distribution board
Plug distribution board
Neutral earthing
Protective shed
Body earthing
Earth pit for body earthing
Earth resistance
Fuses
Loose connection of cable
Housekeeping
Fire extinguisher and type
for
43. Electrical Safety
Employ qualified electrician, preferably ‘B’ license
holders
Display electrical equipment & cable routing layout
All electrical installation to be tested &
commissioned as per BIS codes and IER
All DB’s should be covered
Earthing of all electrical installations
Regular maintenance
44. Records to be maintained, ELCB
Display caution boards
Provide ELCB for portable equipment
24 V hand lamp
Adopt protective system
Insulation
Regular inspection
ELECTRICAL SAFETY
