ELECTRIC SHOCK AND ELECTRIC SHOCK AND EARTHINGEARTHING

Prepared byPrepared by

Shameer N Shameer N & &

Sunder Sunder

ELECTRIC SHOCKELECTRIC SHOCK

Electric ShockElectric Shock

An An electric shockelectric shock can occur upon contact of a human can occur upon contact of a human body with any source of voltage high enough to cause body with any source of voltage high enough to cause sufficient current through the muscles or hair. sufficient current through the muscles or hair.

The minimum current a human can feel is thought to The minimum current a human can feel is thought to be about be about 1 milliampere1 milliampere (mA). (mA).

Effect of Electric shockEffect of Electric shock

Effect of shock depends onEffect of shock depends on Magnitude of the currentMagnitude of the current

VoltageVoltage Body ResistanceBody Resistance

Current path through the body to the earthCurrent path through the body to the earth Duration of contactDuration of contact

Cont..Cont..

Current ValueCurrent Value EffectsEffects

1mA1mA No PerceptionNo Perception

1 – 5 mA1 – 5 mA Sensation of shock, Not painful, individual can still let goSensation of shock, Not painful, individual can still let go

5 – 15mA5 – 15mA Painful shock, Reflex action, individual can still let goPainful shock, Reflex action, individual can still let go

15 – 20mA15 – 20mA Painful shock, Muscular control is lost in the current path, Painful shock, Muscular control is lost in the current path, cannot let gocannot let go

20 – 50mA20 – 50mA Painful muscular contraction leading to light /severe cramp, Painful muscular contraction leading to light /severe cramp, breathing difficultbreathing difficult

50 – 100mA50 – 100mA Paralysis/suffocationParalysis/suffocation

100 – 200mA100 – 200mA Can bear for a very short time. Ventricular fibrillation possibleCan bear for a very short time. Ventricular fibrillation possible

200 – 500mA200 – 500mA Cardiac arrest possible. Even deaths are encounteredCardiac arrest possible. Even deaths are encountered

>500mA>500mA Fatal by longer contact Fatal by longer contact

Death with internal burns. Death with internal burns.

Preventing Electrical ShockPreventing Electrical Shock

Electrical shock appear to be caused by a Electrical shock appear to be caused by a combination of three possible factors:combination of three possible factors: unsafe equipment and/or installation,unsafe equipment and/or installation, workplaces made unsafe by the environment,workplaces made unsafe by the environment, unsafe work practicesunsafe work practices

PrecautionsPrecautions to be taken against Electric shock to be taken against Electric shock

Avoid working onAvoid working on live live electrical parts electrical parts

Wear proper insulating Wear proper insulating boots and glovesboots and gloves as necessary as necessary

Follow Follow Lock-out tag-outLock-out tag-out procedures as required procedures as required

When working on high voltage, make sure that the floor is not When working on high voltage, make sure that the floor is not made of any conducting materialmade of any conducting material

Cont..Cont..

Make sure that no part of your body comes in contact with Make sure that no part of your body comes in contact with earth, metallic casing, metal plates or cross arms when earth, metallic casing, metal plates or cross arms when working on high voltageworking on high voltage

Avoid working at places where your head is liable to touch the Avoid working at places where your head is liable to touch the live parts or mainslive parts or mains

Never touch an energized person with your bare hands but Never touch an energized person with your bare hands but rather use a wooden stick or other non-conductor to push them rather use a wooden stick or other non-conductor to push them away from the source of currentaway from the source of current

Rules for minimizing injury fromRules for minimizing injury from Electrical shock Electrical shock

Cut the power supplyCut the power supply If cutting the electricity is not possible, try to free the victim of If cutting the electricity is not possible, try to free the victim of

electrical shock from contact with the live at once, using a dry electrical shock from contact with the live at once, using a dry stick, dry rope, dry clothing or nonconductor. stick, dry rope, dry clothing or nonconductor. Do not touch him Do not touch him with your bare hands. with your bare hands.

If victim having little or no breathing, provide rescue breathing.If victim having little or no breathing, provide rescue breathing. Never give an unconscious victim any liquids.Never give an unconscious victim any liquids. Efforts to aid a victim should be continued until he revives or is Efforts to aid a victim should be continued until he revives or is

pronounced dead by a physician.pronounced dead by a physician. Also remember that even if electrical burns look minor at the Also remember that even if electrical burns look minor at the

entry and exit points, there might be invisible internal damage. entry and exit points, there might be invisible internal damage. Consult a doctor immediately after an electric shock.Consult a doctor immediately after an electric shock.

Rescue BreathingRescue Breathing Tilt the head back with victim on his back, neck fully Tilt the head back with victim on his back, neck fully

extended.extended.

Elevate victim’s jaw into jutting – out position by inserting Elevate victim’s jaw into jutting – out position by inserting thumb between teeth, grasping lower jaw and lifting it thumb between teeth, grasping lower jaw and lifting it forcefully upward.forcefully upward.

If air passage is not yet cleared, clear at once with several If air passage is not yet cleared, clear at once with several

sharp blows between shoulder blades.sharp blows between shoulder blades.

Open your mouth wide and cover victims mouth completely Open your mouth wide and cover victims mouth completely by placing your mouth over his with airtight contact, also by placing your mouth over his with airtight contact, also closing victim’s nose by pinching it between thumb and closing victim’s nose by pinching it between thumb and finger.finger.

Cont..Cont..

Blow air into victim’s lungs until you see the chest rise (less Blow air into victim’s lungs until you see the chest rise (less forcefully for children); remove your mouth and let him forcefully for children); remove your mouth and let him exhale. If chest does not rise, check steps above.exhale. If chest does not rise, check steps above.

Repeat above step approximately 12 times a minute until Repeat above step approximately 12 times a minute until victim revives (20 times a minute for children).victim revives (20 times a minute for children).

In the case of infants, rescue breathing should be done through In the case of infants, rescue breathing should be done through both the nose and mouth.both the nose and mouth.

If the victim's mouth can't opened, rescue breathing should be If the victim's mouth can't opened, rescue breathing should be applied mouth – to – noise ,rather than mouth – to – mouth.applied mouth – to – noise ,rather than mouth – to – mouth.

General Safety InstructionsGeneral Safety Instructions

Only authorized, competent, and qualified persons are allowed Only authorized, competent, and qualified persons are allowed to work on or around electrical equipment and/ or wiring.to work on or around electrical equipment and/ or wiring.

The person in-charge shall explain the precautions to be taken The person in-charge shall explain the precautions to be taken by the workman before issuing the permit. by the workman before issuing the permit.

Purchase up-to-standard electrical equipment equipped with Purchase up-to-standard electrical equipment equipped with appropriate protective devicesappropriate protective devices

Proper maintenance of system and equipmentProper maintenance of system and equipment

Exercise care: Place yourself in a safe and secure position to Exercise care: Place yourself in a safe and secure position to avoid slipping or stumbling. Make a habit of being cautious. avoid slipping or stumbling. Make a habit of being cautious.

Cont..Cont..

Think carefully before you act. Make sure you are right.Think carefully before you act. Make sure you are right.

Treat everything as live unless it is positively known to be Treat everything as live unless it is positively known to be dead and properly earthed. All voltages are dangerous. Even dead and properly earthed. All voltages are dangerous. Even low voltage shocks may be fatal. low voltage shocks may be fatal.

Extra precautions should be taken when working in Extra precautions should be taken when working in abnormally damp areas. abnormally damp areas.

Follow the Follow the DO’s DO’s and and DON’TsDON’Ts instructions. These should be instructions. These should be displayed in all establishments at places of convenience and displayed in all establishments at places of convenience and personnel trained repeatedly.personnel trained repeatedly.

EARTHINGEARTHING

EarthingEarthing Connecting an equipment to the earth so as to ensure Connecting an equipment to the earth so as to ensure

at all times an immediate & safe discharge of electric at all times an immediate & safe discharge of electric energy due to leakage, faults etcenergy due to leakage, faults etc

Earth potential is taken as zero for all practical Earth potential is taken as zero for all practical purposespurposes

Necessity of EarthingNecessity of Earthing To provide greater safety to personnel & To provide greater safety to personnel &

equipment from the danger of current leakageequipment from the danger of current leakage To maintain a constant voltage in healthy phases in To maintain a constant voltage in healthy phases in

the event of a fault in one phasethe event of a fault in one phase To serve as a return conductor in communication To serve as a return conductor in communication

and traction worksand traction works

Methods of EarthingMethods of Earthing

1.Plate Earthing 1.Plate Earthing

Size of the plate – 60cm x 60cm & 120cm x 120cmSize of the plate – 60cm x 60cm & 120cm x 120cm

Electrode is buried at a depth of at least 1.5mElectrode is buried at a depth of at least 1.5m

Plate material Vs minimum thicknessPlate material Vs minimum thickness

Plate MaterialPlate Material Minimum thicknessMinimum thickness

CopperCopper 3.15mm3.15mm

Galvanized ironGalvanized iron 6.3mm6.3mm

Cast ironCast iron 12mm12mm

Plate EarthingPlate Earthing

2.Pipe or Rod Earthing2.Pipe or Rod Earthing

Used in congested areasUsed in congested areas

The normal size of the G.I. Pipe used is 2 to The normal size of the G.I. Pipe used is 2 to 2.75meter long, 38mm diameter. 2.75meter long, 38mm diameter.

Where rod is used, the length of the rod is between Where rod is used, the length of the rod is between 1.22 to 2.4 m. And the diameter varies between 1.22 to 2.4 m. And the diameter varies between

13 to 19 mm. 13 to 19 mm.

The pipe /rod is driven to a depth of approximately The pipe /rod is driven to a depth of approximately 3m in the ground. 3m in the ground.

Pipe or Rod EarthingPipe or Rod Earthing

3.Strip or Conductor Earthing3.Strip or Conductor Earthing Used in places where the topsoil has got lower resistivity Used in places where the topsoil has got lower resistivity

but underneath it has very high resistivity like a rock etc. but underneath it has very high resistivity like a rock etc.

An approximate length of the stripe is buried in the top soil An approximate length of the stripe is buried in the top soil at a depth of not less than 0.5m to give reasonably low at a depth of not less than 0.5m to give reasonably low earth resistance. earth resistance.

Copper strip if used shall not be less than 25mmx1.6mm in Copper strip if used shall not be less than 25mmx1.6mm in cross section. cross section.

Copper conductor shall not be less thanCopper conductor shall not be less than 23mm

Strip or Conductor EarthingStrip or Conductor Earthing

Double EarthingDouble Earthing

IfIf one earth fails ,then second earth will do the purpose.one earth fails ,then second earth will do the purpose. It offer minimum resistance (as in parallel) to the flow of It offer minimum resistance (as in parallel) to the flow of

leakage current.leakage current. The distance between the two electrode should be 5m The distance between the two electrode should be 5m

approximately .approximately . If the electrode placed near the wall of the building ,minimum If the electrode placed near the wall of the building ,minimum

distance from the wall should be 1.5m.distance from the wall should be 1.5m.

Rules for EarthingRules for Earthing In the case of house wiring ,the earthing must be continuous In the case of house wiring ,the earthing must be continuous

by a single solid conductor of 14 SWG .by a single solid conductor of 14 SWG . All the metallic covering of the main switch,DB,brackets etc All the metallic covering of the main switch,DB,brackets etc

along with the earth point of the wall socket should be earthed.along with the earth point of the wall socket should be earthed. The metallic cover of all medium voltage machines should be The metallic cover of all medium voltage machines should be

earthed by double earthing.earthed by double earthing. In any case the resistance of the earth continuity conductor In any case the resistance of the earth continuity conductor

should not be greater than 1 should not be greater than 1 ΩΩ throughout the system. throughout the system. In case of ordinary soil the earth resistance of the electrode In case of ordinary soil the earth resistance of the electrode

should not be more than 3should not be more than 3ΩΩ and 8 and 8 ΩΩ in rocky soil. in rocky soil.

ReferencesReferences

Electrical Estimation and Costing by N Alagappan & S Electrical Estimation and Costing by N Alagappan & S Ekambaram,T T T I Madras.Ekambaram,T T T I Madras.

Hazards of Electricity and Static Electricity published by Hazards of Electricity and Static Electricity published by Institution of Chemical Engineers,2005.Institution of Chemical Engineers,2005.