Electric shock and fire are two major hazards in electrical installations and we would like to deal with them in some detail. We begin by taking up the prevention and handling of electric shock.
You have learnt in previous Unit that electricity always attempts to travel to the ground and will follow the path of least resistance to get there. If a conductor of electricity becomes available, electric current will follow that path to ground.The tools and equipment you use and even your own body, which is approximately 70% water, are excellent conductors. Becoming part of the path to ground can damage your equipment and can cause serious personal injury including severe burns and even death (Box ).
In Table, we outline the measures that can be taken to prevent and handle electric shock. Technicians who work on electrical installations and equipment can prevent accidents by following these general instructions.
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| Preventing and Handling Electric shock |
Some additional precautions are given below:
• persons other than utility employees should not try to replace street lights or set right service wires;
• the nearest utility office should be informed if loose or hanging wires are noticed;
• take extra precautions when working in abnormally damp areas;
• when, either accidentally or otherwise, live mains and apparatus constitute a danger to persons in a public place, a person should be detailed to stand-by and personally warn the public until the danger has been removed;
• all portable electrical apparatus should be regularly examined, tested and maintained to ensure that the apparatus and leads are in good order;
• all loose wiring, such as flexible cables for portable lamps, tools and trailing cables and other portable and transportable apparatus, should be inspected and tested regularly at frequent intervals to ensure safety;
• while drilling bore wells it should be ensured that the casing pipes do not touch live wires while they are being lifted up;
• unauthorized persons should not
−go near the distribution transformers;
−attempt replacement of transformer fuses;
−touch low lying or snapped conductors;
−lean against electric poles; and
−stand beneath overhead lines while heavy winds are blowing.
Precautions to be taken before providing Temporary Earth
• Ensure that the line / equipment are not live.
• Allow only authorized person to provide temporary earth or remove it.
• Firmly connect insulated wires (for providing earthing) to earth electrode before touching any equipment.
• Take care that the earth wire is not close to other live wires.
• Provide temporary earth on both sides of work spot.
• While disconnecting, first disconnect the earth rods from line / equipment.
• Ensure that the person providing the temporary earth wears rubber gloves/ gauntlets.
• Ensure that the person providing the earthing procedure is at a lower level than the line / equipment being earthed and other workmen are 6 metres away while earthing.
• Do not allow the earthing to be disconnected until the whole work is completed and cleared of people and materials.
• Make sure that while work is being done on a 3 phase line, all conductors are earthed even if work is being done only on one phase.
• Ensure that while one or more workmen are working at a height, others are away so that if tools or materials are dropped accidentally, they are not hurt.
• Every employee should watch his/her counterparts that safety procedures are being followed.
• Whenever a switch is found open, check up why it is kept open, examine the parts of lines and equipment it is controlling and ensure that it is safe to recluse before doing so.
• Ensure that your hands or clothes are not wet while earthing / working. It is unsafe to check whether a line is live or dead with bare hands or other methods.
Line Clears and Precautions
In the course of your work, you would be supervising technical personnel working on various electric lines. Therefore, you should be aware of the associated precautions. We begin with safety around overhead lines.
Safety around Overhead Lines
Overhead power lines are not insulated and looks can be deceiving. What may appear as insulation is weatherproofing material. Wires should not be touched under ANY circumstances.There is a minimum safe distance which should be maintained when working near energized power lines and you have read about it in the previous section.Note that the minimum safe distance increases as the voltage increases. Safe distances also can be affected by weather conditions and other factors.Additional minimum safe distances for various voltages are shown in Table.
• persons other than utility employees should not try to replace street lights or set right service wires;
• the nearest utility office should be informed if loose or hanging wires are noticed;
• take extra precautions when working in abnormally damp areas;
• when, either accidentally or otherwise, live mains and apparatus constitute a danger to persons in a public place, a person should be detailed to stand-by and personally warn the public until the danger has been removed;
• all portable electrical apparatus should be regularly examined, tested and maintained to ensure that the apparatus and leads are in good order;
• all loose wiring, such as flexible cables for portable lamps, tools and trailing cables and other portable and transportable apparatus, should be inspected and tested regularly at frequent intervals to ensure safety;
• while drilling bore wells it should be ensured that the casing pipes do not touch live wires while they are being lifted up;
• unauthorized persons should not
−go near the distribution transformers;
−attempt replacement of transformer fuses;
−touch low lying or snapped conductors;
−lean against electric poles; and
−stand beneath overhead lines while heavy winds are blowing.
Precautions to be taken before providing Temporary Earth
• Ensure that the line / equipment are not live.
• Allow only authorized person to provide temporary earth or remove it.
• Firmly connect insulated wires (for providing earthing) to earth electrode before touching any equipment.
• Take care that the earth wire is not close to other live wires.
• Provide temporary earth on both sides of work spot.
• While disconnecting, first disconnect the earth rods from line / equipment.
• Ensure that the person providing the temporary earth wears rubber gloves/ gauntlets.
• Ensure that the person providing the earthing procedure is at a lower level than the line / equipment being earthed and other workmen are 6 metres away while earthing.
• Do not allow the earthing to be disconnected until the whole work is completed and cleared of people and materials.
• Make sure that while work is being done on a 3 phase line, all conductors are earthed even if work is being done only on one phase.
• Ensure that while one or more workmen are working at a height, others are away so that if tools or materials are dropped accidentally, they are not hurt.
• Every employee should watch his/her counterparts that safety procedures are being followed.
• Whenever a switch is found open, check up why it is kept open, examine the parts of lines and equipment it is controlling and ensure that it is safe to recluse before doing so.
• Ensure that your hands or clothes are not wet while earthing / working. It is unsafe to check whether a line is live or dead with bare hands or other methods.
Line Clears and Precautions
In the course of your work, you would be supervising technical personnel working on various electric lines. Therefore, you should be aware of the associated precautions. We begin with safety around overhead lines.
Safety around Overhead Lines
Overhead power lines are not insulated and looks can be deceiving. What may appear as insulation is weatherproofing material. Wires should not be touched under ANY circumstances.There is a minimum safe distance which should be maintained when working near energized power lines and you have read about it in the previous section.Note that the minimum safe distance increases as the voltage increases. Safe distances also can be affected by weather conditions and other factors.Additional minimum safe distances for various voltages are shown in Table.
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| Minimum Safe Distances around Overhead Power Lines |
We now describe the other safety precautions that need to be observed.
• Till a Line Clear (LC) is received from all sources every line or equipment should be treated as live. No person should get up a pole or work on any lines or equipment unless s/he is specifically authorized to do so. Line clears can be issued or received only by authorized persons. When it is not possible to receive or return line clear in person, the same can be done over telephone but clear identity by way of voice and also a code should be followed. Adequate clearance between lines on which work is being done and other live wires should be ensured or line clears taken on those lines also.
• While issuing line clear
− switch off supply and ensure that the work spot where LC is requisitioned is disconnected from all possible sources of supply;
− ensure personally that all blades of all operating switches are open; and
− discharge the line / equipment using properly earthed discharge rods and by wearing rubber gloves / gauntlets.
• While returning line clear
− only the person who obtained the line clear can return the same;
− the person returning the line clear should ensure that the line / equipment is clear of all people, materials and earthing;
− inform all colleagues that the LC is being returned and that it is no more safe to work on that line/equipment;
− person receiving back the LC should ensure that no more LCs are pending return; and
−the entire team of personnel should stay back until such time as the line/equipment is recharged and leave the work spot only after re-charging.
You may like to go through the following check list before you permit your technicians to work on electric lines.
CHECKLIST BEFORE WORKING ON ELECTRIC LINES
• Have you undergone safety training?
• Have you opened the A B Switch feeding supply?
• Are the LT fuses removed?
• Are cables at Dn box away and not touching it?
• Have you provided temporary earths at work spot?
• Are you wearing gloves?
• Did you check the earth rod in place?
• Are you wearing helmet?
• Have you taken the safety belt with you?
• Are you confident of getting up the pole?
• Did you ensure that all other members in your team are following all safety precautions?
An LC Form needs to be filled up and signed by an authorized person.
Fire Prevention and Protection
Fire can be a major safety hazard in electrical installations and you must know the safety procedures in case of a fire breaking out or to prevent fire. Every substation should train its employees in fire fighting. It should form its own fire fighting team. Teams should be given frequent mock drills. The duty of each member of the fire fighting team should be written and circulated among the staff. A list of all employees with their contact numbers and home addresses should be displayed in the substation.
Box: General Guidelines for Preventing Fire
DOs
• Organize precautionary fire-drill and check fire-fighting apparatus periodically.
• Have sufficient number of fire extinguishers located in strategic positions,so that they may be available for immediate use in various areas.
• Wipe up oil as soon as possible; use sand to cover oil spots.
• Keep flammable material only in special containers and fire-proof rooms.
Keep flammable liquids in approved safety cans and identify them by proper labels. Varnish, paints, lacquers and thinners are highly
inflammable and should be stored away from all open flames or possible sources of ignition. Matches and open flames should not be used where varnish paint or lacquer is being applied with a spray gun.
• Disconnect the supply immediately in case of fire near an electrical apparatus.
• Make sure, when using water hose that the jet of water does not come into contact with live apparatus.
• Be sure that the personnel are familiar with the location and proper use of fire extinguishers in their work area.
DON’Ts
• Do not allow waste paper, rags and other combustible material to accumulate.
• Do not allow open flames and smoking in all such areas where inflammable liquids or gases are stored or being used. Such areas should be posted with appropriate warning signs.
• No employee should smoke or use matches or open flames on customer’s premises unless it is positively known that such action does not conflict with the customer’s rules.
• Do not use fire extinguishers or electrical equipment unless they are clearly marked as suitable for that purpose. Use sand blanket instead.
• Do not throw water on live electrical equipment. It is dangerous to you.
You may need to use fire extinguishers when fire breaks out. In order to be able to use various classes of fire extinguishers, you should know about different types of fire that is categorised according to the materials that are on fire.
• Organize precautionary fire-drill and check fire-fighting apparatus periodically.
• Have sufficient number of fire extinguishers located in strategic positions,so that they may be available for immediate use in various areas.
• Wipe up oil as soon as possible; use sand to cover oil spots.
• Keep flammable material only in special containers and fire-proof rooms.
Keep flammable liquids in approved safety cans and identify them by proper labels. Varnish, paints, lacquers and thinners are highly
inflammable and should be stored away from all open flames or possible sources of ignition. Matches and open flames should not be used where varnish paint or lacquer is being applied with a spray gun.
• Disconnect the supply immediately in case of fire near an electrical apparatus.
• Make sure, when using water hose that the jet of water does not come into contact with live apparatus.
• Be sure that the personnel are familiar with the location and proper use of fire extinguishers in their work area.
DON’Ts
• Do not allow waste paper, rags and other combustible material to accumulate.
• Do not allow open flames and smoking in all such areas where inflammable liquids or gases are stored or being used. Such areas should be posted with appropriate warning signs.
• No employee should smoke or use matches or open flames on customer’s premises unless it is positively known that such action does not conflict with the customer’s rules.
• Do not use fire extinguishers or electrical equipment unless they are clearly marked as suitable for that purpose. Use sand blanket instead.
• Do not throw water on live electrical equipment. It is dangerous to you.
You may need to use fire extinguishers when fire breaks out. In order to be able to use various classes of fire extinguishers, you should know about different types of fire that is categorised according to the materials that are on fire.
Extinguishing Fires
Fire buckets, extinguishers and emulsifiers are the means of fighting fire in power electrical installations. Fire Buckets are of 9litres capacity and filled with sand. These are painted white from inside and post office red colour from outside with “FIRE” written on it. Some fire extinguishers are shown in Fig. If you wish to learn some more details of fire-fighting in electrical installations, you may read Appendix 3. Of course, you and your workforce should know how to use fire extinguishers.
Fire buckets, extinguishers and emulsifiers are the means of fighting fire in power electrical installations. Fire Buckets are of 9litres capacity and filled with sand. These are painted white from inside and post office red colour from outside with “FIRE” written on it. Some fire extinguishers are shown in Fig. If you wish to learn some more details of fire-fighting in electrical installations, you may read Appendix 3. Of course, you and your workforce should know how to use fire extinguishers.
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