SAFETY

Safety precautions: Safety precaution means the prescribed rules for the safety of the personnel and equipment that should be observed in electrical work, otherwise electric shock can be received.

The safety of an electrical installation is ensured by proper insulation, good earthing and by providing fuses in the circuits of that installation.

Electric shock: Electric shock is the sudden convulsion of muscles with the feeling of pain caused by the flow of electric current through the living body.

Factors of severity of an electric shock depends on :

i)                    Magnitude of current flowing through the body

ii)                  Duration of contact with live parts

iii)                Path of current through human body

iv)                The type of supply (AC or DC)

Effects of electric shock according to the flow of current through the human body:

a)      Below 10 mA                           Mild sensation but not painful

b)      10mA to 15mA                        Painful shock but muscles will be in control

c)      15mA to 20mA                        Muscle control will be affected

d)      20mA to 40mA                        Results muscle contractions and breathing will be affected

e)      40mA to 80mA                        Results rapid non-sequential series of contraction of heart

                                                      muscles causing irregular heart beat and possible death.

f)       Above 80mA                            Results severe burns, muscle contraction and stoppage of heart 

                                                     beat causing certain death.

Single phase AC supply is dangerous. In wet condition even 50 volt AC may be dangerous to cause electric shock.

AC voltage is more dangerous than DC voltage because due to more peak value of AC voltage than DC voltage of same level AC voltage is more dangerous. Whenever person comes in good contact with AC voltage he touches peak value (√2 times the r.m.s. value) 100 times in a second and accordingly receives more electric shock.

Necessity to maintain safe clearance between live conductor of an O.H. line and nearest earth point: A the live conductor of an O.H  line is at a certain voltage above earth, the various points of the air medium in between the live conductor and earth point are at different voltages starting from the rated voltage at the conductor surface to zero at earth point. Any physical object existing in between live conductor and earth point is subjected to be at some voltage across its length. If the object is of conducting material the full voltage may appear across the clearance between the live conductor and the nearest point of the object and the gap may flashover at a certain minimum clearance. So to avoid such possibilities of flashover a safe clearance should be maintained between the live conductor and the nearest physical objects.

Action to be taken if a person gets an electric shock: First and foremost duty is to prevent any one else ignorantly rushing out to rescue the victim and then cut off the supply to make the victim free from contact with the live mains either by switching off the mains or by hitting body away from the conductor by means of a dry wooden stick or dry rope, dry clothing or any type of insulating material. The next duty will be to send someone for a doctor. If it is observed that the victim is not unconscious he may be sent to hospital. But if it is found that he is unconscious and stops breathing artificial respiration should be immediately started by a rained person. Artificial respiration should be continued as long as the person is alive and the heart is breathing and until natural respiration starts or the doctor arrives. In the mean time his clothing should be loosened. When the person regains consciousness stimulants should be avoided unless ordered by a doctor.

Precautions to prevent shock:

i)                    All electrical apparatus and equipment should be carefully handled for effective safeguard against injury and death.

ii)                  The damaged or frayed leads should never be used to the appliances.

iii)                The broken switches and plugs should be replaced immediately

iv)                All metallic parts of electrical equipment should be properly earthed.

v)                  Always plug top should be used in plug socket

vi)                Proper working of all the safety devices should be checked periodically

vii)              Correct rating of fuses should be used.

viii)            No electrical appliances should be handled with wet hands

ix)                The live wire or bare wire should not be touched

x)                  No wires or ropes should be tied with the electric poles for drying out the cloths etc.

xi)                All current carrying conductors should be properly insulated.

General safety precautions to be observed for using electricity:

i)                    Unnecessary tampering of any electrical installation, appliances or a machine should be avoided.

ii)                  Proper earthing of all installation should be done and properly maintained. It should be checked periodically.

iii)                To pin plug socket should not be used, always three pin plug socket should be used.

iv)                All single way switches should be installed on the live wires of the circuit.

v)                  For replacing blown fuse or repairing of installation the main switch should be kept in OFF position.

vi)                Any appliances should never be handled with wet hands

vii)              Many appliances should not be connected to one socket

viii)            Plug point, connectors should never be disconnected by pulling connecting wires.

ix)                Electrical equipment should be kept away from water.

x)                  In case of fire, water should not be thrown, CO2 or dry chemical powder or sand should be used.

xi)                Correct rating of fuses should be used.

xii)              Before using portable appliances well earthing of these should be ensured.

Precautions during conducting any electrical maintenance work:

1)      The person in charge, under whose supervision work is to be carried out, himself should see that the switches have been withdrawn and are completely isolated on both sides, links and fuses are opened mains and all apparatus are discharged and earthed properly.

2)      If there is any live apparatus nearby, it should be well protected.

3)      The every action of making the mains and apparatus dead for maintenance work should be entered in the log book or log sheet.

4)      Danger notices should be displayed in conspicuous place on the maintenance job under permit to work.

5)      The nature of work should be explained to the workers by the person in charge in their own language before carrying out.

6)      No work should be done without protecting from risk of shock.

7)      All safety equipment should be checked by the person in charge before issuing the permit to work.

8)      If it is required to work on live mains or apparatus the working person should always be accompanied by a second person and the person in charge should not allow any workman wearing cloths having metal buttons or fitting and shoes with nails. Shoes with rubber sole should be used.

9)      In case of overhead live line maintenance, the works should be carried out by making use of safety belt, gloves etc. in presence of competent supervisor for whole time.

10)  First aid box should be available at the work site.

11)  After completion of work the person in charge should be satisfied himself that the mains and apparatus area quite fit for charging in all respect.

12)  After charging the installation the person in charge should not allow any workman to touch the installation any more.

13)  After completion of the whole process the work permit should be returned to the person in charge and cancelled.

Temporary safety earthing: Before carrying out any repair and maintenance work of electrical equipment installation of temporary earthing of that equipment in order to ensure the safety of the workmen and property is known as temporary safety earthing.

Temporary safety earthing is required for high voltage overhead lines & high voltage plant equipment.

Precautions while installing temporary safety earthing:

1)      Earthing sticks should be insulated and its size should be at least 19 mm dia x 1.5 meters length.

2)      Earthing spikes should be hammered into the soil up to a minimum depth one meter  from ground level

3)      All earthing jumpers should be made of annealed bare and stranded copper conductor of sufficient capacity.

4)      Chains & insulated wires should not be used.

5)      Earthing lead should be connected to earth first before these area connected to the conducting part.

6)      In case of O.H. line lowest conductor should be earthed first.

7)      Earths should be placed on both sides of the working place or equipment.

8)      In case of transformers, switch gears etc. all the phase conductors should be short circuited and earthed.

9)      All static condensers or cables should be discharged and earthed when disconnected from the source of supply.

10)  While removing earthing leads these should be disconnected from the conducting parts first before these are disconnected from the earth spikes.

11)  While connecting or disconnecting earthing leads rubber gloves or gauntlets should be used.

Common safety precautions to be observed in an electrical work:

i)                    No work should be carried out on live electrical equipment. After making the equipment dead it should be effectively earthed before starting the work.

ii)                  Responsible authorized person should work on electrical equipment.

iii)                Shut down before work and resumption of supply after work should be clear cut and full proof.

iv)                There should be some checking whether the prescribed rules are actually observed.

v)                  As far as possible repair work should be carried out during day light hours.

vi)                Staff working on O.H. lines should use proper ladder, safety belts etc. against falling down.

vii)              No electrical work should be done alone.

Precautions for generating equipment:

1)      The load on each generator should not exceed it capacity.

2)      In case of parallel running load sharing among the units should be in proportion to their capacities.

3)      No generator should be disconnected on load. Before disconnecting any generator the load on the said generator should be brought to zero.

4)      The temperature of the generator should not be allowed to go beyond safe limit.

5)      Short circuit fault protection should be kept in perfect order.

6)      First aid box and fire extinguisher should be provided in each generating station.

7)      Shock treatment chart should be fixed at conspicuous place.

Precautions to be taken by lineman while working on overhead line:

i)                    A lineman should not touch an overhead line before making the line dead and properly earthed.

ii)                  The overhead line should not touch an overhead line before making the line dead and properly earthed.

iii)                The lineman should put on safety belt while working on a pole.

iv)                While working on live lines rubber gloves of appropriate voltage grad should be used.

v)                  When a ladder is used it should be held by another person on the ground to prevent its slipping down.

Minimum distance should be maintained by lineman for operating:

1)      6.6 kV                                      0.6 M

2)      11 kV                                       0.9 M

3)      33 kV                                       1.2 M

4)      66 kV                                       2.0 M

5)      132 kV                                     3.5 M

6)      220 kV                                     4.5 M

Steps are to be taken in case of electric fire:

i)                    First of all the electric supply to be firing place should be disconnected immediately

ii)                  Water should not be thrown on a live conductor. It is dangerous. Dry sand or liquid CO₂ or proper fire extinguishing powder should be used for putting out fire.

iii)                Nearest switching station should be informed in case of occurrence of fire in distribution lines and doctors should be informed in case of any injury or casualty.

Precautions to be taken by an electrician in handling tools:

i)                    The sharp edged tools should never be put in pocket without shield.

ii)                  During work hand or finger should not be placed in front of the moving cutting tools.

iii)                During cutting with a sharp ended chisel the motion of the tools should be always away from the body of the electrician.

iv)                The handle of the hammer should be examined before use whether it is properly secured and free from oil or grease.

v)                  The tools after use should never be left at the top of the ladder or any other high level place which may cause serious injury by accidental falling down.

vi)                The electrician should be careful whether the tools are suitable to match the need of the work.

vii)              Any type of injury should be attended immediately without delay, which may cause infection.