Elements of Electrical Engineering & Electronics


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Elements of Electrical Engineering & Electronics

  1. 1. EEE-201 28.02.2014 1 | P a g e Elements of Electrical Engineering & Electronics Electric motor An electric motor is an electric machine that converts electrical energy into mechanical energy. Found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives, electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as from the power grid, inverters or generators. Small motors may be found in electric watches. General-purpose motors with highly standardized dimensions and characteristics provide convenient mechanical power for industrial use. The largest of electric motors are used for ship propulsion, pipeline compression and pumped-storage applications with ratings approaching a megawatt. Electric motors may be classified by electric power source type, internal construction, application, type of motion output, and so on. Working Principle of Electric Motor An electric motor is a device which converts electrical energy into mechanical energy. A common motor works on direct current. So, it is also called DC motor.When a rectangular coil carrying current is placed in a magnetic field, a torque acts on the coil which rotates it continuously.When the coil rotates, the shaft attached to it also rotates and thus it is able to do mechanical work. Armature A D.C. motor consists of a rectangular coil made of insulated copper wire wound on a soft iron core. This coil wound on the soft iron core forms the armature. The coil is mounted on an axle and is placed between the cylindrical concave poles of a magnet.
  2. 2. EEE-201 28.02.2014 2 | P a g e Elements of Electrical Engineering & Electronics Working of a DC Motor When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn towards the right, causing rotation.When the coil turns through 900, the brushes lose contact with the commutator and the current stops flowing through the coil. However the coil keeps turning because of its own momentum. Now when the coil turns through 1800, the sides get interchanged. As a result the commutator ring C1 is now in contact with brush B2 and commutator ring C2 is in contact with brush B1. Therefore, the current continues to flow in the same direction. Electric generator Electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric current to flow through an external circuit. The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, awind turbine, a hand crank, compressed air, or any other source of mechanical energy. Generators provide nearly all of the power for electric power grids. How Generators Work Generators are useful appliances that supply electrical power during a power outage and prevent discontinuity of daily activities or disruption of business operations. Generators are available in different electrical and physical configurations for use in different applications. In the following sections, we will look at how a generator functions, the main components of a generator, and how a generator operates as a secondary source of electrical power in residential and industrial applications. It is important to understand that a generator does not actually ‘create’ electrical energy. Instead, it uses the mechanical energy supplied to it to force the movement of electric charges present in the wire of its windings through an external electric circuit. This flow of electric charges constitutes the output electric current supplied by the generator. This mechanism can be understood by considering the generator to be analogous to a water pump, which causes the flow of water but does not actually ‘create’ the water flowing through it.The modern-day generator works on the principle of electromagnetic induction discovered by Michael Faraday in 1831-32. Faraday discovered that the above flow of electric charges could be induced by moving an electrical conductor, such as a wire that contains electric charges, in a magnetic field. This movement creates a voltage difference between the two ends of the wire or electrical conductor, which in turn causes the electric charges to flow, thus generating electric current.
  3. 3. EEE-201 28.02.2014 3 | P a g e Elements of Electrical Engineering & Electronics Main components of a generator The main components of an electric generator can be broadly classified as follows (refer to illustration above): (1) Engine (2) Alternator (3) Fuel System (4) Voltage Regulator (5) Cooling and Exhaust Systems (6) Lubrication System (7) Battery Charger (8) Control Panel (9) Main Assembly / Frame A description of the main components of a generator is given below. (1) Engine The engine is the source of the input mechanical energy to the generator. The size of the engine is directly proportional to the maximum power output the generator can supply. There are several factors that you need to keep in mind while assessing the engine of your generator. (2) Alternator The alternator, also known as the ‘genhead’, is the part of the generator that produces the electrical output from the mechanical input supplied by the engine. It contains an assembly of stationary and moving parts encased in a housing. The components work together to cause relative movement between the magnetic and electric fields, which in turn generates electricity. (3) Fuel System The fuel tank usually has sufficient capacity to keep the generator operational for 6 to 8 hours on an average. In the case of small generator units, the fuel tank is a part of the generator’s skid base or is mounted on top of the generator frame. For commercial applications, it may be necessary to erect and install an external fuel tank. All such installations are subject to the approval of the City Planning Division. Click the following link for further details regarding fuel tanks for generators. (4) Voltage Regulator As the name implies, this component regulates the output voltage of the generator. The mechanism is described below against each component that plays a part in the
  4. 4. EEE-201 28.02.2014 4 | P a g e Elements of Electrical Engineering & Electronics cyclical process of voltage regulation. This cycle continues till the generator begins to produce output voltage equivalent to its full operating capacity. As the output of the generator increases, the voltage regulator produces less DC current. Once the generator reaches full operating capacity, the voltage regulator attains a state of equilibrium and produces just enough DC current to maintain the generator’s output at full operating level. When you add a load to a generator, its output voltage dips a little. This prompts the voltage regulator into action and the above cycle begins. The cycle continues till the generator output ramps up to its original full operating capacity. (5) Cooling & Exhaust Systems Continuous usage of the generator causes its various components to get heated up. It is essential to have a cooling and ventilation system to withdraw heat produced in the process. Raw/fresh water is sometimes used as a coolant for generators, but these are mostly limited to specific situations like small generators in city applications or very large units over 2250 kW and above. Hydrogen is sometimes used as a coolant for the stator windings of large generator units since it is more efficient at absorbing heat than other coolants. Hydrogen removes heat from the generator and transfers it through a heat exchanger into a secondary cooling circuit that contains de-mineralized water as a coolant. (6) Lubricating System Since the generator comprises moving parts in its engine, it requires lubrication to ensure durability and smooth operations for a long period of time. The generator’s engine is lubricated by oil stored in a pump. You should check the level of lubricating oil every 8 hours of generator operation. You should also check for any leakages of lubricant and change the lubricating oil every 500 hours of generator operation. (7) Battery Charger The start function of a generator is battery-operated. The battery charger keeps the generator battery charged by supplying it with a precise ‘float’ voltage. If the float voltage is very low, the battery will remain undercharged. If the float voltage is very high, it will shorten the life of the battery. Battery chargers are usually made of stainless steel to prevent corrosion. They are also fully automatic and do not require any adjustments to be made or any settings to be changed. The DC output voltage of the battery charger is set at 2.33 Volts per cell, which is the precise float voltage for lead acid batteries. (8) Control Panel This is the user interface of the generator and contains provisions for electrical outlets and controls. The following article provides further details regarding the generator control panel. Different manufacturers have varied features to offer in the control panels of their units (9) Main Assembly / Frame
  5. 5. EEE-201 28.02.2014 5 | P a g e Elements of Electrical Engineering & Electronics All generators, portable or stationary, have customized housings that provide a structural base support. The frame also allows for the generated to be earthed for safety. Transformer A transformer is a static electrical device that transfers energy by inductive coupling between its winding circuits. A varying current in the primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux through the secondary winding. Figure 1-1 structural schematic diagram of transformer A wide range of transformer designs are used in electronic and electric power applications. Transformers are essential for the transmission, distribution, and utilization of electrical. No-load state of Transformer: viz. the disconnecting state between he secondary winding and load (Figure 1-2). Connect the primary winding and the power supply of AC voltageU1, and then it will produce alternating current I0, this current is called no-load currents. This current set up alternating magnetic flowφ0 which is closed along iron core magnetic circuit. At the same time, it traverses the primary winding and secondary winding, and then produces inducting electromotive forceE2 (secondary no-load voltage). Working Principle of transformer The working principle of transformer is very simple. It depends upon Faraday’s laws of Electromagnetic Induction. Actually mutual induction between two or more winding is responsible for transformation action in an electrical transformer. Faraday’s laws of Electromagnetic Induction According to these Faraday’s laws, "Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or coil". Basic Theory of Transformer
  6. 6. EEE-201 28.02.2014 6 | P a g e Elements of Electrical Engineering & Electronics Say you have one winding which is supplied by an alternating electrical source. The alternating current through the winding produces a continually changing flux or alternating flux surrounds the winding. If any other winding is brought nearer to the previous one, obviously some portion of this flux will link with the second. As this flux is continually changing in its amplitude and direction, there must be a change in flux linkage in the second winding or coil. According to Faraday’s laws of Electromagnetic Induction, there must be an EMF induced in the second. If the circuit of the latter winding is closed, there must be an electric current flows through it. This is the simplest form of electrical power transformer and this is most basic of working principle of transformer.Naturally emf will be induced in it as per Faraday’s laws electromagnetic induction. This is the most basic concept of theory of transformer The winding which takes electrical power from the source, is generally known as Primary Winding of transformer. Here in our above example it is first winding. The winding which gives the desired output voltage due to mutual induction in the transformer, is commonly known as Secondary Winding of Transformer. Here in our example it is second winding The above mentioned form of transformer is theoretically possible but not practically, because in open air very tiny portion of the flux of the first winding will link with second so the electric current flows through the closed circuit of latter, will be so small that it may be difficult to measure. Circuit breaker A switch that automatically interrupts the flow of electric current if the current exceeds a preset limit, measured in amperes. Circuit breakers are used most often as a safety precaution where
  7. 7. EEE-201 28.02.2014 7 | P a g e Elements of Electrical Engineering & Electronics excessive current through a circuit could be hazardous. Unlike fuses, they can usually be reset and reused. How They Work In a circuit breaker, electricity generates a current in an electromagnet. The electromagnet is strong enough to pull down on a lever that is connected either to a spring or to another electromagnet. When the electrical flow exceeds design tolerances, the bar snaps down, thus cutting off electrical flow. Simple Domestic Circuit Breakers Simple domestic circuit breakers are designed to prevent damage to home wiring. Damage is usually caused by plugging too many high power devices, like electric heaters, appliances and high power lights, in to a circuit. When the circuit breaker senses the overload, it trips interrupting the flow of electricity and preventing damage to home wiring. Ground Fault Circuit Breakers Ground fault, or GFI, circuit breakers are designed more to prevent shocks to people. A GFI circuit breaker is a solid state device that senses when there is a ground fault. Ground faults often occur when an electrical device is dropped in water or the user is standing in water. GFI breakers are usually found in kitchens, bathrooms and other rooms where water is often found. Commercial Circuit Breakers
  8. 8. EEE-201 28.02.2014 8 | P a g e Elements of Electrical Engineering & Electronics Commercial circuit breakers are designed to protect extremely high voltage circuits. The basic working principles are the same, but some large commercial breakers include digital or solid state circuitry to sense and calculate pre-defined safety criterion in commercial applications. Switch In electrical engineering, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is non conducting. A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another work piece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used to automatically control a system. For example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be padlocked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock.Practical switches fall short of this ideal; they have resistance, limits on the current and voltage they can handle, finite switching time, etc. The ideal switch is often used in circuit analysis as it greatly simplifies the system of equations to be solved, however this can lead to a less accurate solution. Theoretical treatment of the effects of non-ideal properties is required in the design of large networks of switches, as for example used in telephone exchanges.
  9. 9. EEE-201 28.02.2014 9 | P a g e Elements of Electrical Engineering & Electronics Electric Cable There are times when a power cord or cord set is not readily available for a given application. The plug may be unavailable in a molded configuration. There may be times when the designer or manufacturer would prefer to wait until just prior to shipping to install a plug on the equipment. If the equipment requires more than 3.0–3.5 KVA (kilovolts), or is using three-phase power, a molded-on plug/socket International cable is similar in appearance to North American cable, but there are a number of important differences. International cable is sometimes referred to as “harmonized,” or simply “HAR.” This comes from the European standards to which the cable is constructed: CENELEC publications HD-21 and HD-22. “HD” (Harmonized document), which is the European Union’s effort to provide consistency in manufacturing cable in Europe. HD-21 is the standard for PVC- jacket cable and HD-22 is the standard for rubber cable. Cable manufactured outside Europe cannot exhibit the “HAR” marking. In this case the cable must be manufactured to the IEC standards for cable: IEC 60227 for PVC jacketed cable and IEC 60245 for rubber jacketed cable. As is the case for North American cable, each jacket type offers advantages and disadvantages.The aluminum acts to pick up stray electrical charges, usually from “bleeding off” within the cable, where the charge may cause interference. Commonly, the aluminum is attached to the ground of the cable to facilitate dispersal of the stray charge. It is important to note that international standards do not call for, nor do they recognize shielded cable. The cable may be built to harmonized standards, but it will not carry any approvals. North American shielded cable, on the other hand, will carry UL and CSA approvals. Custom Lengths Interpower is well equipped to provide cable packaged to your company’s specifications. We maintain a large inventory of most of the cable described in this catalog. We can deliver your order on spools in quantities that you specify. We can also deliver cable cut to length so that you eliminate scrap. This service is well suited with large cables that are expensive and difficult to handle. Stripping Interpower uses stripping equipment that makes it easy to strip all of the cables listed in this section. Our striping machines strip conductors up to 50cm. We can also cut and strip conductors to specified lengths and apply crimp terminations which one can specify from a wide variety that we maintain in stock. Standard stock terminations include: ultrasonic weld, ring terminals, spade terminals, straight-style disconnects, flag-style quick disconnects, and ferrules. Our cable stripping and crimp termination services are particularly attractive with large rubber jacketed cable that is difficult to strip and handle.
  10. 10. EEE-201 28.02.2014 10 | P a g e Elements of Electrical Engineering & Electronics Terminations Interpower can make your complete power cable assemblies by terminating the cable with any of the following: straight blade or locking type plugs and connectors, international plugs and connectors, IEC 60309 high power pin and sleeve devices, IEC 60320 connectors, and related devices. Manufacturing Our skilled assemblers work in a well-equipped, comfortable manufacturing facility that is ISO 9001 Certified. Continuous training enables our assemblers to perform the wide variety of work that moves through our shop. This assures a quick turnaround time and cable assemblies that will meet your specifications. Assuming that appropriate materials are specified, our power cable assemblies are UL recognized or listed and CSA certified. ElectricalWiring Electrical wiring can be as simple as following these tips. Connecting cords, circuit connections, device connections, and electrical panel connections all require some type of wiring connection. This tutorial is loaded with electrical wiring tips to make the job simple and easy to accomplish. Whether you're a first-timer or an old pro who just needs a few refresher tips, having a hands-on lesson will make the job that much easier. Sometimes, having the right tools for the job is just as important as knowing how to do the task. These electrical wiring tips will make your electrical projects a snap Appliance Wiring: Timothy Thiele
  11. 11. EEE-201 28.02.2014 11 | P a g e Elements of Electrical Engineering & Electronics Every appliance, whether it be a counter top appliance like a coffee pot or a major appliance like an electric range, has an electrical connection. Each has a specific outlet and certain breaker size that they are needed to be connected to. These connections are easy enough if you can follow these simple instructions. Electrical Wiring Connection - Good and Bad: There are good electrical connections and some that should never be made. Although manufacturers sometimes give you the choice of a couple of different connection points, like with switches and outlets, a closer look will reveal which connection should be your choice. Keep these connection tips in mind the next time you perform your next electrical wiring project. Electrical Service Wiring: Making the proper connections to the electrical service components will help keep the electricity flowing trouble-free. Before trying to wire an electric meter, disconnect, electrical panel, or sub- panel, be sure you know where to place the wires on each. Here's a look at just a few that will help you keep your wiring projects safe and functional for years to come. Electrical Device Wiring:
  12. 12. EEE-201 28.02.2014 12 | P a g e Elements of Electrical Engineering & Electronics Electrical devices must be wired right to make electrical connections safe and secure. Some appliances need only 120-volt outlets, but others need 240-volt outlets. Just connecting wires to device terminals isn't enough. You need to know the proper way to strip, bend and tighten connections so they will provide you with a safe and functional connection for years to come. Wiring Size and Application: Before you can make electrical connections, you must first know what type wire to use for the installation, what color wire is needed for the application, and what is the proper size wire to handle the load of the circuit. For electricians, wire colors mean everything. They identify whether the wire is a hot, neutral, or a ground wire. Distribution board A distribution board (or panel board) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, in a common enclosure. Inside a North American panel
  13. 13. EEE-201 28.02.2014 13 | P a g e Elements of Electrical Engineering & Electronics The picture to the right shows the interior of a standard residential service, North American General Electric style breaker panel. The three power lines can be seen coming in at the top (One going to the neutral busbar to the left with all the white wires, the other two attached to the main breaker). Below it are the two rows of circuit breakers with the circuit's hot wire leading off. A line can be seen directly exiting the box and running to a NEMA 5-15electrical receptacle with a power cord plugged into it. This picture shows the interior of a typical UK distribution panel. The three incoming phase wires connect to the busbars via a main switch in the centre of the panel. On each side of the panel are two bus bars, for neutral and earth. The incoming neutral connects to the lower busbar on the right side of the panel, which is in turn connected to the neutral busbar at the top left. The incoming earth wire connects to the lower busbar on the left side of the panel, which is in turn connected to the earth busbar at the top right. The cover has been removed from the lower-right neutral bar; the neutral bar on the left side has its cover in place. The two-pole RCBOs in the picture are not connected across two phases, but have supply-side neutral connections exiting behind the phase bus bars. The illustrated panel includes a great deal of unused space; it is likely that the manufacturer produces 18- and 24-position versions of this panel using the same chassis. Location and designation A three phase service drop enters through the side of this main service panel consisting of three 100 ampere fuses. Large buildings or facilities with higher electric power demand may have multiple circuit breaker panels. In this case, the panels are often indicated by letters of the alphabet. One case is The Decon Gallery, a modern building in downtown Toronto, which has 11 breaker panels designated A, B, C, D, and so on. A backstage outlet is therefore labeled C27. In many such buildings, each outlet is on its own circuit breaker, and the outlets are labelled in the above specified manner to facilitate easy Distribution boards may be surface-mounted on a wall or may be sunk into the wall. The former arrangement allows for easier alteration or addition to wiring at a later date, but the latter arrangement may look neater, particularly in a residential situation. The other problem with recessing a distribution board into a wall is that if the wall is solid a lot of brick or block may
  14. 14. EEE-201 28.02.2014 14 | P a g e Elements of Electrical Engineering & Electronics need to be removed - for this reason recessed boards are generally only fitted on new-build projects when the required space can be built into the wall. Mobile operation Sometimes it is desired to have a portable breaker panel, for example, for special events. In this case, a breaker panel is mounted to a board, together with various sockets. The American one pictured at the right has a cord with an L21-30 plug to supply power. Power leaves the board through four three-phase circuits: three 15 ampere circuits; and one 20 A circuit. The 15 A circuits each go to a triplex-box. The 20 A circuit goes to an L21-20 receptacle, and one leg of it goes to a 20 A duplex receptacle shown at the upper left. The neon night-lights on the upper right triplex box are to show the phase presence. Overview The Restriction of Hazardous Substances (ROHS) Directive aims to minimize the environmental impact of waste electrical and electronic equipment, by reducing the quantities of four heavy metals and two brominated flame retardants that it may contain. Electricalsubstation A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. The word substation comes from the days before the distribution system became a grid.
  15. 15. EEE-201 28.02.2014 15 | P a g e Elements of Electrical Engineering & Electronics A 50 Hz electrical substation in Melbourne. This is showing three of the five 220 kV/66 kV transformers, each with a capacity of 150 MVA. This substation is constructed using steel lattice structures to support strain bus wires and apparatus.A 115 kV to 41.6/12.47 kV 5 MVA 60 Hz substation with circuit switcher, regulators, reclosers and control building at Warren. This substation shows elements of low-profile construction; apparatus is mounted on in dividual columns. Elements of a substation 1. A:Primary power lines' side B:Secondary power lines' side Primary power lines 2.Ground wire 3.Overhead lines 4.Transformer for measurement of electric voltage 5.Disconnect switch 6.Circuit breaker 7.Current transformer 8.Lightning arrester 9.Main transformer 10.Control building 11.Security fence 12.Secondary power lines
  16. 16. EEE-201 28.02.2014 16 | P a g e Elements of Electrical Engineering & Electronics Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Smaller distribution stations may use recloser circuit breakers or fuses for protection of distribution circuits. Substations themselves do not usually have generators, although a power plantmay have a substation nearby.Where a substation has a metallic fence, it must be properly grounded to protect people from high voltages that may occur during a fault in the network. Earth faults at a substation can cause a ground potential rise. Substations may be described by their voltage class, their applications within the power system, the method used to insulate most connections, and by the style and materials of the structures used. for example,Transmission substation. A transmission substation connects two or more transmission lines.The simplest case is where all transmission lines have the same voltage. In such cases, substation contains high-voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. A transmission station may have transformers to convert between two transmission voltages, voltage control/power factor correction devices such as capacitors, reactors or static VAR compensators and equipment such as phase shifting transformers to control power flow between two adjacent power systems. Transmission substations can range from simple to complex. A small "switching station" may be little more than a bus plus some circuit breakers. The largest transmission substations can cover a large area (several acres/hectares) with multiple voltage levels, many circuit breakers and a large amount of protection and control equipment (voltage and current transformers, relays and SCADA systems). Modern substations may be implemented using international standards such as IEC Standard 61850. Short circuit A low-resistance connection established by accident or intention between two points in an electric circuit. The current tends to flow through the area of low resistance, bypassing the rest of the circuit. an abnormal condition of relatively low resistance between two points of differing potential in a circuit, usu. resulting in a flow of excess current. An electrical path in a circuit that causes most of the current to flow around or away from some other path in the circuit. Accidental short circuits, especially between the high and low voltages of a power supply, can cause very strong current to flow, possibly damaging or overheating the circuit.
  17. 17. EEE-201 28.02.2014 17 | P a g e Elements of Electrical Engineering & Electronics Electric Shock & MedicalTreatment Electric Shock Introduction Electric current passing through the body, particularly alternating current at power frequencies of 50 Hz and 60 Hz, may disrupt the nervous system, causing muscular reaction and the painful sensation ofelectric shock. The most common reaction is to be thrown off the conductor as a result of the muscular contraction. However, in a small number of instances, the consequence is death from cardiac arrest, or from ventricular fibrillation (where the heart muscle beats in a spasmodic and irregular fashion) or from respiratory arrest. The impedance of the body is determined by the magnitude of the touch voltage (there being an inverse relationship between impedance and voltage) and other factors, such as the wetness of the skin, the cross-sectional area of contact with the conductors, and whether or not the skin is broken or penetrated by the conductors. As a general rule of thumb, at an applied voltage of 230 V at 50 Hz, the total body impedance for a hand-to-feet path will be in the range 1000 Ω to 2500 Ω for most of the population, falling to around 750 Ω at voltages in excess of about 1000 V.
  18. 18. EEE-201 28.02.2014 18 | P a g e Elements of Electrical Engineering & Electronics Figure: - Depiction of a typical indirect contact electric shock The path that the current takes through the body has a significant effect on the impedance. For example, the impedance for a hand-to-chest path is in the order of 50 per cent of the impedance for a hand-to-foot path. Moreover, the current’s path through the body is a significant determinant of the effect on the heart. Medical Treatment or Electric Shock Treatment Electrical shocks always need emergency medical attention -- even if the person seems to be fine afterward. Brief low-voltage shocks that do not result in any symptoms or burns of the skin do not require medical care. For any high-voltage shock, or for any shock resulting in burns, seek medical care at a hospital's Emergency Department. A doctor should evaluate electric cord burns to the mouth of a child. Treatment of electric shock depends on the severity of the burns or the nature of other injuries found.  Burns are treated according to severity. o Minor burns may be treated with topical antibiotic ointment and dressings. o More severe burns may require surgery to clean the wounds or even skin grafting. o Severe burns on the arms, legs, or hands may require surgery to remove damaged muscle or even amputation.  Other injuries may require treatment. o Eye injuries may require examination and treatment by an ophthalmologist, an eye specialist. o Broken bones require splinting, casting, or surgery to stabilize the bones. o Internal injuries may require observation or surgery.