Electrical Safety

In the next 45 min We will refresh our knowledge about, Hazards related to electricity Shock & Factors affecting shock Shock protection measures Residual Current Circuit Breaker Site Specific Requirements Systems & Procedures related to Electrical Safety

ELECTRIC SHOCK It is sudden & accidental stimulation of the human body’s nervous system as a result of passage of electric current

Primary Hazards Electric shock Electric fire & explosion Electric flash Electric burns

Secondary Hazards Person falling from height Dropping of tools & objects Health hazards due to release of toxic gas & production of UV rays Psychological effects

How Shock Occurs You will receive a shock if you touch two wires at different voltages at the same time (Phase to Phase, Phase to Neutral, Phase to Ground) Flashover involving part of human body

By simultaneously touching the phase and neutral conductor thus completing the circuit through his body R Y B N LOAD HAVING METALLIC BODY ALTERNATOR

2. By touching the phase conductor and standing on the ground ELEC. EQPT.HAVING METALLIC BODY ALTERNATOR R Y B

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

Resistance Amount of Current Severity of Shock Path of Flow Voltage

Path of flow of current in the Human Body

Body Resistance Body area Resistance (ohms) Dry skin 1,00,000 to 6,00,000 Wet skin 1000 to 5000 Internal body - Hand foot 400 to 600 Ear to ear

Person in touch P with live wire N I = V / R POWER SOURCE N I = V / R = 230 / 100000 A (Dry Condition) = 0.0023 A = 2.3 mA I = 230 / 5000 (Wet Condition) = 0.046 A = 46 mA

Effect of Electric Current on Human Body

Voltage Higher the voltage - Higher the severity of shock.

PROTECTION FROM ELECTRICAL INJURIES PREVENTION OF ELECTRICAL ACCIDENTS

Shock Protection Measures Isolation Double insulation Earthing Over Current Protection Devices Residual Current Protection Devices

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

OVERCURRENT PROTECTION FUSE KITKAT TYPE HRC TYPE Miniature Circuit Breaker (MCB) Fuses are proven safety devices for overload conditions Check the fuses for their current ratings Never replace fuse wire with ordinary copper or aluminium wire High rupturable cartridge (HRC) fuses are now a days easily available and has advantages over traditional fuses

Double Insulation Insulation Another insulation added. Double insulated power tools have non-metallic body Need not be earthed (two point plug is sufficient) Insulation Functional Protective

SYMBOL FOR DOUBLE INSULATED MACHINES Double Insulation Elec. Machine Metallic Body Elec. Machine Nonconductive Body SYMBOL FOR DOUBLE INSULATED MACHINES

Two Distinct Equipment Earthing NEUTRAL EARTHING EQUIPMENT EARTHING Two Distinct Equipment Earthing

CORE BALANCE CURRENT TRANSFORMER RCCB WORKING PRINCIPLE No fault Condition I1 = I2 Fault Condition I1 > I2 (I1 = I2 + IP) Tripping Condition IP > 30 mA T EQUIPMENT L I1 I2 Ip N CORE BALANCE CURRENT TRANSFORMER

RCCB & RCBO IS 12640 - Part 1, 2000 Residual current operated circuit breakers. Part 1: Circuit breakers without integral over current protection. ( RCCBs) (First Revision) IS 12640 - Part 2, 2001 Residual current operated circuit breakers for house hold and similar uses - Part 2: Circuit breakers with integral over current protection. ( RCBOs) (First Revision)

RCCB (RESIDUAL CURRENT CIRCUIT BREAKER)

Residual Current Circuit Breaker Standard Specification, 30 mA sensitivity , 63Amps, 4 poles. Testing procedure Testing the sensitivity Test the RCCB weekly and record it.

Typical Sub Distribution Board ELCB 63 A 30 mA

HAND LAMPS Protect from contact and damage, 24V hand lamps are to be used.To be enclosed by glass surrounded by metal wire mesh

Portable Power Tools

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

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”

Lockout and Tagging of Circuits Apply locks to power source after de-energizing Tag deactivated controls Tag de-energized equipment and circuits at all points where they can be energized Tags must identify equipment or circuits being worked on

Registers & Procedures Weekly RCCB check register Lockout / Tagout Permit system

Clues that Electrical Hazards Exist Tripped circuit breakers or blown fuses Warm tools, wires, cords, connections, or junction boxes Frequent tripping of RCCB Worn or frayed insulation around wire or connection

Discussion

Thank You