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Transcript of Electrical Safety
SAFETY Clifford Almazan Basic Concepts
of Electricity Zenia Concepcion Effects of Electricity
on the Human Body Charlie Zulueta Electrical Hazards Rochelle Monsayac Electrical Safety Devices Arra Tuason Electrical Safety Work Practices Electricity is the set of physical phenomena associated with the presence and flow of electric charge. Electricity gives a wide variety of well-known effects, such as lightning, static electricity, electromagnetic induction and the flow of electrical current. In addition, electricity permits the creation and reception of electromagnetic radiation such as radio waves. Basic Concepts of Electricity In Electrical Engineering, electricity is used for:
Electric power where electric current is used to energize equipment.
Electronics which deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies. Basic Concepts of Electricity
The word electricity is from the New Latin ēlectricus, "amber-like", coined in the year 1600 from the Greek ήλεκτρον (electron) meaning amber, because electrical effects were produced classically by rubbing amber.
The earliest recorded observations about electricity date from about 600 BC and are attributed to the Greek philosopher Thales of Miletus. He noted that when amber, a fossil resin, was rubbed it would attract feathers or bits of straw.
In 1951, Jerome Cardam distinguished the difference between the attractive properties of amber and magnetite. He also envisioned electricity as a type of fluid. English physician William Gilbert in 1600 published his book about magnets. He gave a proof that attraction exhibited by amber was not magnetic. He also proposed that the earth is a huge magnet. About 1736, the French chemist Charles-Francois Du Fay learned that rubbing glass and rubbing resinous substances seemed to produce charges of different kinds. He found that two charges of the same kind repel while unlike charges attract. He suggest that electricity may consist of two kinds of invisible fluid which he named vitreous and resinous. History In 1747, the statesman and inventor Benjamin Franklin of United States who is credited with the invention of the lightning rod, proposed a single fluid theory of electricity. According to his theory only one kind of charge is mobile. The two types of electric behaviour that found on rubbed amber and that found on rubbed glass are due to a deficiency or an excess of the more mobile kind of charge, transferred during rubbing. Franklin designated the effect produced by rubbing glass as positive electricity and that produced by rubbing amber as negative electricity.
The quantitative development of electricity began late in the 18th century. In 1753, the Englishman Henry Cavendish and Charles Augustin de Coulomb of France(1785) discovered independently the inverse-square law for stationary charges. An Italian physicist Alessandro Volta invented the battery as a source of electricity in 1800. The magnetic effect arising from electric currents was demonstrated in 1820 by a Danish physicist Hans Christian Oersted. In 1826, the German physicist Georg Simon Ohm announced discoveries concerning voltage, current, and resistance in circuits. The unit of current ampere was named after the French scientist Andre-Marie Ampere who worked out many fundamental laws of electrodynamics. History The production of induced electric currents by changing magnetic field was demonstrated by an English chemist Michael Faraday in 1831. Scottish physicist James Clerk Maxwell presented his theory of electromagnetic field in 1865. History BRANCHES OF ELECTRICITY
-Electrostatics or Static Electricity –the study of interactions that occur when electricity is at rest.
-Electrodynamics or Current Electricity –the study of the relations between electrical, magnetic, and mechanical phenomena when electricity is in motion. Basic Concepts of Electricity
(Charge on a gold-leaf electroscope causes the leaves to visibly repel each other)
Electric charge is a property of certain subatomic particles, which gives rise to and interacts with the electromagnetic force, one of the four fundamental forces of nature. Charge originates in the atom, in which its most familiar carriers are the electron and proton. It is a conserved quantity, that is, the net charge within an isolated system will always remain constant regardless of any changes taking place within that system. Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as a wire. The informal term static electricity refers to the net presence (or 'imbalance') of charge on a body, usually caused when dissimilar materials are rubbed together, transferring charge from one to the other.
Definition of terms Electric current
(An electric arc provides an energetic demonstration of electric current)
The movement of electric charge is known as an electric current, the intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Definition of terms Electric field
(Field lines emanating from a positive charge above a plane conductor)
Electric field is an especially simple type of electromagnetic field produced by an electric charge even when it is not moving (i.e., there is no electric current). The electric field produces a force on other charges in its vicinity. Moving charges additionally produce a magnetic field. Definition of terms Electric potential
(A pair of AA cells. The + sign indicates the polarity of the potential difference between the battery terminals)
Electric potential is the capacity of an electric field to do work on an electric charge, typically measured in volts. This definition of potential, while formal, has little practical application, and a more useful concept is that of electric potential difference, and is the energy required to move a unit charge between two specified points. The volt is so strongly identified as the unit of choice for measurement and description of electric potential difference that the term voltage sees greater everyday usage. Definition of terms Electromagnets
(Magnetic field circles around a current)
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off. Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnets for picking up and moving heavy iron objects like scrap iron. Definition of terms
The electric motor exploits an important effect of electromagnetism: a current through a magnetic field experiences a force at right angles to both the field and current. Definition of terms Electric circuit
(A basic electric circuit. The voltage source V on the left drives a current I around the circuit, delivering electrical energy into the resistor R. From the resistor, the current returns to the source, completing the circuit.)
An electric circuit is an interconnection of electric components such that electric charge is made to flow along a closed path (a circuit), usually to perform some useful task.
Definition of terms Types of circuits
There are two types of electrical circuits – series and parallel.
A series circuit is defined as a circuit in which the elements in a series carry the same current, while voltage drop across each may be different.
Definition of terms
A parallel circuit is defined as a circuit in which the elements in parallel have the same voltage, but the currents may be different. Definition of terms The components in an electric circuit can take many forms, which can include elements such as resistors, capacitors, switches, transformers and electronics. Electronic circuits contain active components, usually semiconductors, and typically exhibit non-linear behaviour, requiring complex analysis. The simplest electric components are those that are termed passive and linear: while they may temporarily store energy, they contain no sources of it, and exhibit linear responses to stimuli.
The resistor is perhaps the simplest of passive circuit elements: as its name suggests, it resists the current through it, dissipating its energy as heat. The resistance is a consequence of the motion of charge through a conductor: in metals, for example, resistance is primarily due to collisions between electrons and ions. Ohm's law is a basic law of circuit theory, stating that the current passing through a resistance is directly proportional to the potential difference across it. The resistance of most materials is relatively constant over a range of temperatures and currents; materials under these conditions are known as 'ohmic.' The ohm, the unit of resistance, was named in honour of Georg Ohm, and is symbolised by the Greek letter Ω. 1 Ω is the resistance that will produce a potential difference of one volt in response to a current of one amp. Definition of terms
The capacitor is a development of the Leyden jar and is a device capable of storing charge, and thereby storing electrical energy in the resulting field. Conceptually, it consists of two conducting plates separated by a thin insulating dielectric layer; in practice, thin metal foils are coiled together, increasing the surface area per unit volume and therefore the capacitance. The unit of capacitance is the farad, named after Michael Faraday, and given the symbol F: one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected to a voltage supply initially causes a current as it accumulates charge; this current will however decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit a steady state current, but instead blocks it.
The inductor is a conductor, usually a coil of wire that stores energy in a magnetic field in response to the current through it. When the current changes, the magnetic field does too, inducing a voltage between the ends of the conductor. The induced voltage is proportional to the time rate of change of the current. The constant of proportionality is termed the inductance. The unit of inductance is the henry, named after Joseph Henry, a contemporary of Faraday. One henry is the inductance that will induce a potential difference of one volt if the current through it changes at a rate of one ampere per second. The inductor's behaviour is in some regards converse to that of the capacitor: it will freely allow an unchanging current, but opposes a rapidly changing one. Definition of terms In each plant, the mechanical movement of different equipment is caused by an electric prime mover (motor). Electrical power is derived from either utilities or internal generators and is distributed through transformers to deliver usable voltage levels.
Electricity is found in two common forms:
• AC (alternating current)
• DC (direct current)
Basic Electrical Concepts
Electrical equipment can run on either of the AC/DC forms of electrical energies. The selection of energy source for equipment depends on its application requirements.
Basic Electrical Concepts
Industrial AC voltage levels are roughly defined as LV (low voltage) and HV (high voltage) with frequency of 50–60 Hz. An electrical circuit has the following three basic components irrespective of its electrical energy form:
1. Voltage (measured in volts) is defined as the electrical potential difference that causes electrons to flow.
2. Current (measured in amperes) is defined as the flow of electrons.
3. Resistance (measured in ohms) is defined as the opposition to the flow of electrons.
All three are bound together with Ohm’s law, which gives the following relation between the three: V = I × R
Basic Electrical Concepts Power
In DC circuits, power (watts) is simply a product of voltage and current: P =V × I
For AC circuits, the formula holds true for purely resistive circuits; however, for the following types of AC circuits, power is not just a product of voltage and current.
Apparent power is the product of voltage and ampere, i.e., VA or kVA is known as apparent power. Apparent power is total power supplied to a circuit inclusive of the true and reactive power.
Real power or true power is the power that can be converted into work and is measured in watts
Reactive power. If the circuit is of an inductive or capacitive type, then the reactive component consumes power and cannot be converted into work. This is known as reactive power and is denoted by the unit VAR.
Basic Electrical Concepts Relationship between powers
Apparent power (VA) = V × A
True power (Watts) = VA × cosφ
Reactive power (VAR) = VA × sinφ
Power factor is defined as the ratio of real power to apparent power. The maximum value it can carry is either 1 or 100(%), which would be obtained in a purely resistive circuit.
Power factor = True power / Apparent power
Basic Electrical Concepts
A transformer is a device that transforms voltage from one level to another. Transformer working is based on mutual emf induction between two coils, which are magnetically coupled. When an AC voltage is applied to one of the windings (called as the primary), it produces alternating magnetic flux in the core made of magnetic material (usually some form of steel). The flux is produced by a small magnetizing current which flows through the winding. The alternating magnetic flux induces an electromotive force (EMF) in the secondary winding magnetically linked with the same core and appears as a voltage across the terminals of this winding. Cold rolled grain oriented (CRGO) steel is used as the core material to provide a low reluctance, low loss flux path. The steel is in the form of varnished laminations to reduce eddy current flow and losses on account of this.
Basic Electrical Concepts Transformer
Basic Electrical Concepts There is a very simple and straight relationship between the potential across the primary coil and the potential induced in the secondary coil. The ratio of the primary potential to the secondary potential is the ratio of the number of turns in each and is represented as follows: N1/N2 = V1/V2
When the transformer is loaded, then the current is inversely proportional to the voltages and is represented as follows: N1/N2 = V1/V2= I2/I1
Basic Electrical Concepts TYPES OF ELECTRICAL INJURY reflex response possible involving trauma which occurs when electrical current passes over or through a worker’s body. ELECTRIC SHOCK Occurs when electrical current passes over or through a worker’s body resulting in a fatality. ELECTROCUTION Electric shock may cause muscles to contract causing a worker to lose his or her balance and fall. FALLS occur when a worker contacts energized electrical wiring or equipment.
they most often occur on the hands and feet. BURNS SEVERITY OF THE SHOCK 1. The path of the current through the body.
2. The amount of current flowing through the body.
3. The length of time the body is in circuit. The severity of the shock depends on three factors: THE HUMAN BODY RESISTANCE MODEL CURRENT AND ITS EFFECT ON THE HUMAN BODY -Improper grounding
-Exposed electrical parts
-Wet conditions Electrical hazards A ground is a physical
electrical connection to the earth. Grounding is the process used to eliminate unwanted voltage. Electrical hazards Improper grounding Grounding reduces the risk of being shocked or electrocuted. Electrical equipment must
be properly grounded. Electrical hazards Improper grounding Never remove the
ground pin. The ground pin safely
returns leakage current
to ground. Electrical hazards Improper grounding If you contact exposed live electrical parts, you will be shocked Exposed wires or terminals are hazardous. Electrical hazards Exposed Electrical parts You can get shocked! Removing the ground pin removes an important safety feature. Electrical hazards Improper grounding Electrical hazards Exposed Electrical parts On construction sites, temporary lighting must be properly guarded and protected to avoid contact with broken bulbs and avoid potential shocks. Make sure your power tools are being used with a properly rated extension cord. Use properly rated extension cords. Electrical hazards Inadequate wiring DIFFERENT TYPES OF WIRES WITH THEIR ELECTRICAL
CURRENT RATING Electrical hazards Inadequate wiring Never use tools or extension cords with damaged insulation. Insulation prevents conductors from contacting each other or you. Defective or inadequate
insulation is a hazard. Electrical hazards Damaged Insulation Never attempt to repair a damaged cord with tape. Electrical hazards Damaged Insulation Do not run extension cords through doors or windows. Never hang extension cords from nails or sharp objects. Electrical hazards Damaged Insulation Wires and other components
in an electrical system or circuit have a
maximum amount of current they can
carry safely Overloaded circuits
can cause fires. Electrical hazards Overloaded Circuits Wet conditions are hazardous. Damaged insulation increases the hazard. Electrical hazards Wet Conditions Electrical hazards Wet Conditions Water increases the risk
of electric shock. Always avoid using tools
in wet locations. An overcurrent protective device consisting of a metal strip, ribbon, or wire which is designed to open an electric circuit by melting if a predetermined current is exceeded. Fuses interrupts an electric current in a circuit when the current becomes too high
a pair of contacts conducting the current are separated by preloaded springs or some similar mechanism.
Can be reset (Automatically or manually) Circuit breakers designed to prevent electrical shock by quickly breaking the circuit when there is a difference in the currents in the hot and neutral wires.
The GFCI continually measures electricity flowing within a circuit to detect any loss of current. If the current passing through the circuit fluctuates a minute amount from that returning (to complete the circuit) , the GFCI instantaneously switches the power off to the affected circuit. The GFCI interrupts power within milliseconds to prevent a lethal dose of electricity. Ground Fault Circuit Interrupters (GCFIs) protects electrical equipment against voltage spikes
to limit the voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold Surge protectors Safety First Always "De-energized parts." Live parts to which an employee may be exposed shall be de-energized before the employee works on or near them.
"Energized parts." If the exposed live parts are not de-energized (i.e., for reasons of increased or additional hazards or infeasibility), other safety-related work practices shall be used to protect employees who may be exposed to the electrical hazards involved. "Lockout and Tagging." While any employee is exposed to contact with parts of fixed electric equipment or circuits which have been de-energized, the circuits energizing the parts shall be locked out or tagged or both in accordance with the standard requirements.
"Overhead lines." if work is to be performed near overhead lines, the lines shall be deenergized and grounded, or other protective measures shall be provided before work is started. "Illumination." Where lack of illumination or an obstruction precludes observation of the work to be performed, employees may not perform tasks near exposed energized parts. Employees should not reach blindly into areas which may contain energized parts.
"Confined or enclosed work spaces." The employee shall use, protective shields, protective barriers, or insulating materials as necessary to avoid inadvertent contact with exposed energized parts.
"Conductive materials and equipment." Conductive materials and equipment that are in contact with any part of an employee's body shall be handled in a manner that will prevent them from contacting exposed energized conductors or circuit parts. Electrical injuries Alternating current (AC) and Direct Current (DC) electrical supplies can cause a range of injuries including:
Loss of muscle control
Thermal burns Electric shock
A voltage as low as 50 volts applied between two parts of the human body causes a current to flow that can block the electrical signals between the brain and the muscles. Effect is dependent upon a large number of things including the size of the voltage, which parts of the body are involved, how damp the person is, and the length of time the current flows.
When an electrical current passes through the human body it heats the tissue along the length of the current flow. This can result in deep burns that often require major surgery and are permanently disabling Loss of muscle control
People who receive an electric shock often get painful muscle spasms that can be strong enough to break bones or dislocate joints. This loss of muscle control often means the person cannot ‘let go’ or escape the electric shock. The person may fall if they are working at height or be thrown into nearby machinery and structures.
Overloaded, faulty, incorrectly maintained, or shorted electrical equipment can get very hot, and some electrical equipment gets hot in normal operation. People can receive thermal burns if they get too near hot surfaces or if they are near an electrical explosion. Work precautions There are some simple precautions that can be taken that will significantly reduce the risk of electrical injury to you:
Work near electricity
Work using electrically powered equipment
Maintaining electrical equipment
Electricity in potentially explosive atmospheres Work near electricity
-Do a risk assessment for the work you are planning, and make sure this covers electrical hazards.
-Learn how to recognise electrical wires.
-Work away from electrical wiring wherever possible. If you have to work near electrical wiring or equipment, ask for the electrical supply to be turned off. Make sure the power is off, and cannot be turned on again without you agreeing.
-Identify where it is safe to work. Put up danger notices where there are still live electrical circuits, and warn your co-workers where it is safe to work and where it is not safe. Remember to remove notices at the end of the work. Work using electrically powered equipment
You should make sure that electrical equipment used for work is safe. Here are a list of actions that should be taken to ensure this is so:
-Perform a risk assessment to identify the hazards, the risks arising from those hazards, and the control measures you should use.
-Check that the electrical equipment is suitable for the work and way in which it is going to be used.
-Check that the electrical equipment is in good condition.
-Make sure that the user of the equipment is trained to use it safely and can keep others safe.
-Make sure the user knows which personal protective equipment to wear, how to use it, and make sure they do. Maintaining electrical equipment safety
The law requires electrical equipment to be maintained to prevent danger. The type and frequency of user checks, inspections and testing needed will depend on the equipment, the environment in which it is used and the results of previous checks.
Electricity in potentially explosive atmospheres
Areas which may have explosive atmospheres
The use of electricity can generate hot surfaces or sparks which can ignite an explosive atmosphere. An explosive atmosphere could be present in a variety of different places including paint spray booths, near fuel tanks, in sumps, or many places where aerosols, vapours, mists, gases, or dusts exist. Equipment and explosive atmospheres
Electrical and non electrical equipment and installations in potentially explosive atmospheres must be specially designed and constructed so that the risks of ignition are eliminated or reduced.
Equipment for use in explosive atmosphere should be regularly inspected and maintained to ensure it does not pose an increased risk of causing a fire or explosion. Maintenance of the equipment should only be carried out by people who are competent to do so. Electrical Safety Precautions Gella Chavez -Unplug unused appliances
-Do not drape clothes, toys or other items over warm appliances.
-Always follow appliance instructions carefully
-Keep all electrical appliances away from water such as sinks, bathtubs, pools or overhead vents that may drip
-Do not operate any electrical appliance with wet hands or while standing in water
-Keep clothes, curtains, toys and other potentially combustible materials at away from radiators, space heaters, heating vents and other heat sources. Appliances -Check cords regularly for frays, cracks or kinks, including power tool cords, holiday lights and extension cords.
-Cords are not be jump ropes, clothes lines or leashes, and should never be used for anything other than their intended purpose.
-Cords should be firmly plugged into outlets
-Do not staple or nail cords in position at any time
-Cords should not be placed beneath rugs
-Use the proper weight and length of extension cord for the appropriate task, and be sure the cord is rated for indoor or outdoor use, whichever is required.
When unplugging a cord, pull on the cord at the outlet rather than tug on the cord itself. Cords -Block unused outlets by changing to a solid cover plate or using childproof caps.
-Do not overload outlets with multiple adaptors or power strips; relocate cords instead.
-Never put any object other than the appropriate size plug into an outlet.
-Keep all outlets properly covered with secure plates that cover all wiring. Outlets -Use bulbs that have the correct wattage requirements for each fixture.
-Consider switching to more efficient compact fluorescent (CFL) bulbs that provide the same level of light at a lower wattage level.
-Always screw bulbs in tightly
-Be sure to unplug or turn off a fixture completely before changing light bulbs. Light Bulbs -Keep trees pruned and away from power lines overhead as well as where the power lines approach the house.
-Do not fly kites, model aircraft or balloons near power lines.
-When using a ladder, carefully inspect the surrounding area to be sure it is free from power lines.
-Always assume that contact with a power line can be deadly.
-Do not approach a downed power line to see if it is live Outdoors -Do not allow children to play in proximity to small or large electric appliances.
-Replace any tools that put off even mild electric shocks.
-Replace any light switches that have a tendency to flicker.
-Replace any light switches that are hot to the touch.
-Avoid overloading extension cords, sockets and plugs.
-Do not every force a three-prong plug into a two-receptacle socket.
-Know where fuse boxes and circuit breakers are located as well as how to properly operate them.
-Never attempt electrical repairs or rewiring without proper certification and experience
-Do not put water on an electrical fire; use a dry fire extinguisher or baking soda instead. Electrical Fire Safety