2. ELECTRIC SHOCK Occurs when electrical current passes through the body Causes devastating injuries or even death Because our bodies are good conductors of electricity. When a part of our body completes an electric circuit, we get an electric shock You will receive a shock if you touch two wires at different voltages at the same time.

3. Accidental contact with exposed electrical wiring Contact with a high voltage source Contact with a person who is receiving an electric shock Contact with a live and neutral wires Due to a lightning strike Poking metal objects into an electrical outlet Touching an electrical appliance with wet hands

4. MACRO SHOCKS  Most common type of shock  Occurs when current flows across intact skin and through the body MICRO SHOCKS  Occurs when there is a direct current path to the heart tissue  Usually these shocks are from inside the skin, i.e. a malfunctioning pacemaker, or ungrounded catheter etc.

5. A basic electric circuit has three components: voltage, current, and resistance. The killer component is current. According to Ohm’s law, V= IR Resistance of the body varies from one person to another, moisture content between different layers of skin Typical skin resistance : 500 Ω (moist skin) to 300,000 Ω (dry skin) The low resistance of wet skin allows current to pass into the body more easily and give a greater shock.

6.  The amount of electrical current through the body  The duration of the current through the body  The path of the current through the body  The muscle structure of the person

7. MaleFemale Electric Sensation0.5mA and 1mA 0.25mA to 0.5mA Uncomfortable SensationGreater than 1mA to 2mA Maximum threshold level15mA9mA Electrical shocks can occur in several forms, and the given description applies to various levels Electrical Shock Fibrillation level: This is a function of current over time. For example, you will get fibrillation with 500mA over 0.2 sec or 75mA over 0.5 sec. Let-go threshold: This is the current level at which humans lose muscle control; the electricity causes muscles to contract until current is removed.

8. 1.Burns  Heating due to resistance can cause extensive and deep burns.  Voltage levels of 500 to 1000 volts tend to cause internal burns  Damage due to current is through tissues

9. *A domestic power supply voltage (110 or 230 V), 50 or 60 Hz AC current through the chest for a fraction of a second may induce ventricular fibrillation. If not immediately treated by defibrillation, fibrillations are usually lethal. All the heart muscle cells move independently instead of in the coordinated pulses needed to pump blood to maintain circulation. *Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all.

10.  Current can cause interference with nervous control, especially over the heart and lungs.  Repeated or severe electric shock which does not lead to death has been shown to cause neuropathy.  Recent research has found that functional differences in neural activation during spatial working memory and implicit learning oculomotor tasks have been identified in electrical shock victims.  When the current path is through the head, it appears that, with sufficient current, loss of consciousness almost always occurs swiftly.

11.  Upto 80 percent of its electrical injuries involve thermal burns due to arcing faults.  Electric welders protect themselves using face shields with dark glass, heavy leather gloves, and full-coverage clothing.  The heat produced may cause severe burns, especially on unprotected flesh.  The blast produced by vaporizing metallic components can break bones and irreparably damage internal organs.

12. current effects  1 mA Perception level  5 mA Slight shock felt  6-30 mA Painful shock  50-150 mA Extreme pain  1000-4,300 mA Ventricular fibrillation  10,000+ mA Cardiac arrest, death.

13.  First separate victim from the electrical source.  Turn off the power supply switch and disconnect the plug.  Turn off the main power supply or pull out the fuse.  Or simply pull the victim away from the electrical source.  Do NOT touch the victim with your bare hands, or the electric current will pass through you as well.

14.  Inspect wiring of equipment before each use.  Replace damaged electrical cords immediately.  Use safe work practices  Know the location and how to operate shut-off switches and/or circuit breaker panels.  Use these devices to shut off equipment in the event of a fire or electrocution.  Limit the use of extension cords.  Use only for temporary operations.  In all other cases, request installation of a new electrical outlet.  Use only multi-plug adapters equipped with circuit breakers or fuses.

15.  Medical uses 1.ECT 2.Pain relief  Law enforcement & personal defence  Torture  Capital punishment.

17.  Earthing is the process of connecting an earth conductor to the earth electrode. It helps to prevent electric shocks by providing a low impedance, low resistance, return path for any fault current to get back to the distribution panel. This high return fault current will cause the circuit's breaker to trip and disconnect the fault. If something goes wrong inside the appliance and the Live wire touches the metal case, then the Earth wire acts like a Neutral wire and completes the circuit for the electricity. A very large current suddenly flows because the metal case has little resistance. This large current blows the fuse in the plug and disconnects the appliance from the power supply.

18.  The first letter indicates the connection between earth and the power-supply equipment (generator or transformer): T: Direct connection of a point with earth (Latin: terra) I: No point is connected with earth (isolation), except perhaps via a high impedance.  The second letter indicates the connection between earth and the electrical device being supplied: T: Direct connection of a point with earth. N: Direct connection to neutral at the origin of installation, which is connected to the earth.   TT: transformer neutral earthed, and frame earthed,  TN: transformer neutral earthed, frame connected to neutral,  IT: unearthed transformer neutral, earthed frame

19. In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer. The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N).

20.  TN-S: separate protective earth (PE) and neutral (N) conductors from transformer to consuming device, which are not connected together at any point after the building distribution point.

21. TN-C: combined PE and N conductor all the way from the transformer to the consuming device.

22. TN-C-S earthing system: combined PEN conductor from transformer to building distribution point, but separate PE and N conductors in fixed indoor wiring and flexible power cords.

24. IT network In an IT network, the distribution system has no connection to earth at all, or it has only a high impedance connection. In such systems, an insulation monitoring device is used to monitor the impedance.

25. The main objectives of the earthing are to :  Provide an alternative path for the fault current to flow so that it will not endanger the user.  Ensure that all exposed conductive parts do not reach a dangerous potential.  Maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment.  To protect the human being from disability or death from shock in case the human body comes in contact with the frame of any electrical machinery due to leakage or fault.  To protect tall buildings and structures from atmospheric lightning.

26.  Neutral Earthing is connecting 3 phase star points of transformers and 3 phase generators and neutral bus/wire to station earthing system.  Equipment Earthing is connecting a non-current carrying metallic parts of electrical plant to station earth.(earth electrode/earth mat.)

27.  Any pipe, plate or wire embedded in the earth is called earth electrode.  The earth is conventionally considered to be an infinite storehouse of charges and is therefore at zero potential for all practical purposes.  Therefore any current which is excess can be sent to the earth, this is earthing.  Earthing needs to be done specific to the situation and location of the building for which it is done.

28.  Good conductor of electricity  Should not be corrodible or oxidized easily  Lesser length in comparison to area of cross section  Dependence of conductance is on depth.  Burying it too deep will result in faults in wiring.  Conductive substances like coke and salt in alternate layers.

29.  Plate earthing  Pipe earthing  earthing through water main  Horizontal Strip earthing  Rod earthing

30.  Copper or G I plate of dimensions (60 cm X 60 cm X 3.18 mm) or (60 cm X 60 cm X 6.3 mm)  Faces vertical.  Buried in 15 cm thick layers of coke alternately with soil.  G.I. Pipe of diameter 15 cm and length 60 cm encases the earth wire  Salt water is regularly poured through a funnel to increase conductivity.  Drawback -faults in the earth wire cannot be observed easily resulting in huge losses.

31.  G I Pipe of diameter around 38mm and length 2m is embedded in the ground at depth 4.75 metres.  Leading wire has large diameter to carry fault current safely and is enclosed in G I tube.  Periodic checks for faults in the wire possible.  Advantage over plate earthing- circular cross section. More surface area is in contact with the soil and so it can handle greater leakage current.  Disadvantage - more material and you have to put in more excavation work.

32.  Earthing connected through the pipes that supply water itself.  Possible only if water supply pipe is made of G I.  Main copper lead for the wire fanned out, soldered with lead pipe and bent around entire main pipe.  Drawbacks- lot of faults, shocks and electrolytic conduction. Not very affordable.

33.  Basic construction is the same.  Only shape of the electrode differs as the name suggests.  Not very efficient. Require more volume of metal for construction.  Need to be buried deeper as they are not able to easily overcome soil resistance.  Hence it is difficult to check faults as well.

34. Neutral Wire Earth Wire  Neutral is connected to the neutral point of the transformer and is earthed only at the substation.  Carries return current in single phase and out of balance current in 3 phase load  Earth wire originates from the earth electrode and during transmission, every 1.6 km it is earthed at 4 equally spaced points.  Earth wire carries current only in case of a fault. If the neutral wire is broken, do NOT be tempted to replace it with earth wire. This is giving the earth wire a non zero potential and it is extremely dangerous if there is an excess current.