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Wednesday, 21 September 2016

Safety in Electricity

Safety in Electricity 




Objectives
 



Primary Hazards


Electrical shock


Severity of shock Depends


Body Resistance



Effect of Electrical current on Human Body


How shock occurs




Shock protection methods


Isolation




Isolation switches


Isolation Transformer


Low voltage


Double Insulation


Electrical safety


Check in General for


Sub distribution Board


Plug Tops


Earthing


Earthing scheme for construction power facilities


Details of Earthing station with GI pipe.



Transformer Neutral Earthing - size of earth lead.


Equipment Earthing


Fuses


ELCB Working Principle


ELCB - Earth Leakage Circuit Breaker


ELCB - Earth Leakage Circuit Breaker


Causes of Electrical fire


Failure of insulation level


Electrical Burns


Electrical Flash


Cable Routing


Cables


Protecting cables from Damages


Cable joints


Hand lamps


Manpower


Register & Procedures


Electrical safety


Electrical safety


Thank you


Welcome to
Safety In Electricity session


Primary Hazards
Electric shock
Electric fire & explosion
Electric flash

Electric burns
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
Severity of Shock Depends
Duration of flow
Amount of current
Path of flow of current
Type of energy 
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
Effect of Electric Current on Human Body
How Shock Occurs
By simultaneously touching the phase and neutral conductor thus completing the circuit through his body
 By touching the phase conductor and standing on the ground
By touching a metallic part that has become live by itself being in contact with an energised wire

Shock Protection Methods
uIsolation
Current limitation
Low voltage
Double insulation
Earthing
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
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
Isolation Transformer
Power  can be tapped from isolation transformer

Avoids shock between earth and phase  

Low Voltage
v24V hand lamps.

vBy 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.                                                                                                                                                         
Double Insulation
Another insulation added.
Double insulated power tools have non-metallic body

Need not be earthed (two point plug is sufficient)
Electrical Safety
Site requirements
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
PLUG TOPS
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.
Fuses
uFuses are proven safety devices for overload conditions
uCheck the fuses for their current ratings
uNever replace fuse wire with ordinary copper or aluminium wire
uHigh rupturable cartridge (HRC) fuses are now a days easily available and has advantages over traditional fuses
ELCB WORKING PRINCIPLE 
ELCB
(EARTH LEAKAGE CIRCUIT BREAKER
For portable power tools  power  supply is taken through ELCB
Saves persons from electric shock
Earth Leakage Circuit Breaker
For portable power tools  power  supply should be taken through ELCB
ELCB’s OF 30 mA sensitivity , 63Amps, 3 poles
Test the ELCB weekly and record it.
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.
 Static electricity.

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.
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
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

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
Cables 
Single phase supply
Phase - red
Neutral - black
Earth - green
Three phase supply
Phases
Red
Yellow
Blue
Neutral - black

PROTECTING CABLES FROM DAMAGES
Protection against mechanical damages
Protection against heat
Cables should be laid away from welding cables
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
u
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
Manpower 
Employ qualified electrician, preferably ‘B’ license holders

Identification of the electrician - red helmet
Registers & Procedures
Weekly ELCB check register
Lockout / Tagout
Permit system
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

Records to be maintained, ELCB
Display caution boards
Provide ELCB for portable equipment
24 V hand lamp
Follow rules and regulations
Follow safety measures
Adopt protective system
Insulation
Regular inspection

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(1) What are the precautions to be taken while handling and storing compressed cylinders? (1) What are the safety requirements for doing a hot work? (1) What are the scaffoldings and its kinds and it’s Consists? (1) What are the type of fire extinguishers commonly used and briefly (1) What is a guard rail system? (1) What is a life-line? (1) WHAT IS A NEARMISS? (1) WHAT IS ACCIDENT? (1) What is an “Assembly Point" and Head counting procedure? (1) What is color coding system? (1) What is Confined Space? (2) What is different between a flash back arrestor and a check valve? (1) What is Evocation? (1) What is excavation? (1) What is Fire (1) What is First Aid and CPR? (1) What is heat stroke? What are the different stage through which a person undergoes before he gets heat stroke? (1) What is lock-out/tag-out system? (1) What is LOTO? (1) What is method statement? (1) What is MSDS ? (1) What is Radio activity? (1) What is Risk Assessment? (1) What Is Safe working Load (SWL)? 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