UNIT 5 TEST Flashcards
Factors of electric shock
- amount a path of current
- type of voltage (AC or DC)
- value of voltage
- length of time the body is energized
- condition of the skin
- area of contact
Amount of current on the body (lethal and non lethal)
Non lethal: 1-50mA, 1-8 the shock is felt but not painful, the victim can let go
20-50mA the shock is very painful, victim cannot let go. There are severe contractions
Lethal: 50-200mA severe muscular contractions and nerve damage. Possible ventricular fibrillation of the heart causing death
Over 200mA severe burns and muscular contractions occur
Most common voltage that causes death, threshold is considered high voltage
-Contact with 120 volts AC the common household voltage has led to more deaths than with any other voltage
-AC voltage of above 750 volts are considered high voltage
-DC voltages can be very dangerous, industrial voltages as small as 42 volts DC can be lethal
-Victims of high voltage shock usually respond well to artificial respiration, because the low voltage shock causes twitching of the walls of the heart which interferes with sudden restoration of normal pulses
Rescuing shock victims
- most important is to ACT FAST, the resistance of the victim decreases with time and the victim can die in just a few seconds
- protect yourself (DO NOT touch the energized victim)
- free the victim from electrical contact
- apply CPR or artificial respiration
Proper locking out and tagging procedures
- lock out must involve more than disconnecting the power source, electrically denergized machinery that has its hydraulic systems still pressurized has killed workers
- make all energy sources including; electrical, pneumatic hydraulic or gravitational inoperative (this is what you call zero mechanical state)
- you should have your own lock and key, these are only used to lock out energy sources
- only person permitted to remove lock is the individual who placed the lock on the machinery
Who is responsible for a permit and when an electrical permit is required
- It is the responsibility of the electrical contractor or others responsible for carrying out the work to obtain a permit from the local electrical inspection department before commencing work
- a copy of the electrical permit must remain posted in a place on the site of the work until completion of the electrical inspection
- responsible persons must notify the inspection department in writing that work is ready for inspection
- permit completion of the electrical inspection before concealing any work
Atomic structure
- Neutrons
- Protons
- Electrons
Electrical charges of subatomic particles
- the electron carries the basic unit of electrical charge
- electrons charge is considered to be a negative charge, because its free to move an electron actively participates in the transfer of electrical energy
- protons carry a positive charge, opposite to that of an electron
- it has the same size of charge as the electrons negative one
- protons are not directly active in the flow of electrical energy, but they do influence the flow of electrons
Difference between good conductor and good insulator
- materials like copper and aluminum have electrons that are easy to free, they re said to have many free electrons and are conductors
- materials like glass and rubber have electrons that are very difficult to free. They are said to have few free electrons and are insulators
Insulators block the transfer of electrical energy
Law of electrical charges
Negatively charged particles repel other negatively charged particles. They tend to move away from each other
Positively charged particles repel each other
Negatively charged particles attract positively charged particles, they tend to move to each other
Because of this law:
Protons (+) and electrons (-) attract each other
Protons repel other protons
Electrons repel other protons
Electrons repel electrons
Five ways electricity is produced and example of each type
- Heat = thermoelectrcity
- Magnetism = electromagnetism
- Chemicals = electrochemistry
- Pressure = piezoelectricity
- Light = photoelectricity
Good insulators and good insulating materials
- household wiring consists of pure copper conductors a plastic layer of insulation, this insulation provides protection from electric shock and prevents short circuiting of the system
- plastics, glass and porcelain at high voltages function as insulators
- glass is a good insulator and in long lengths it provides adequate insulation for very high voltages
Good conductors and good conducting materials
- most metals are good conductors such as silver is the best pure metal conductor, with copper in second
- techs also use aluminum, for high voltage transmission lines
- conductors heat up when current is flowing through them
Difference between alternating and direct current
Direct current: current that flows in a constant direction
Alternating current: regularly reverses direction and occurs during reversal of polarity of each of the conductor, which is always the case with house current
Electromotive force (EMF)
Potential difference of an energy source
Ex. Battery or generator
Potential: positive or negative, measured at one point with respect to another
Potential difference: difference in potential between any two points in a circuit
Voltage: alternative term for potential difference
Components of electrical circuit
- an energy source (battery or a wall plug)
- conductors (connecting wires)
- load (device that uses electrical energy to do work)
Voltage in electrical circuits compares to pressure in water circuit
- Electric current is the movement of electrons along a conductor
- an electric circuit is like the flow of water through a piping system
- in a piping system you can measure the pressure of the water and the volume of water flowing through the system at any point
- for the water to flow through the pipe, there must be a difference in pressure,the water flows several points in the piping system, it will be lower at each point as measured in the direction of flow
Amperage in electrical circuit compares to flow in water circuit
- you use a pump to pump water through the piping and back to the tank
- the piping system has a valve that you can open and close to control the amount of water to flow
- if the pump is running and the valve is fully open, there is very little restriction to the flow of water through the piping system
- if you partially close the valve to increase the restriction, expect a reduced amount of water flowing (gallons per minute)
Electrical circuit: a battery is connected to a variable electrical resistance. In a DC circuit, a battery acts like the pump in a water circuit
Circuit protection devices
- Fuses
- Circuit breakers
- Thermal and magnetic overloads
