Chapter 15. Book 1 Introduction To Electricity. Flashcards
What is electricity?
 molecule is the smallest identifiable, particle or substance molecules are made up of smaller particles called atoms, which are neither protons or electrons. The structure of an atom consist of a center of protons, carrying a positive charge with a shell of electrons rotating around the protons, when a single electron is loosely attracted to the mass of protons, it can easily be freed from the atom, when a battery or generator can force an electron to move, allowing another electron from an adjacent atom to rush in and take its place flow of an electric current is made
Voltage drop
Whenever work is done, voltage drop results if large loads are placed in a circuit thicker wires must be used so that voltage will not drop to the point where it cannot force sufficient current through the wires. The rate at which current flows is expressed in amperes voltage drop and amperage is affected by wire length, size resistance, and condition of the wire.
Switches
A two way wall switch controls, lighting outlets at one location well, a three way switch provides control from two different locations. Like at the top and bottom of a stairway low-voltage switch in is a switch that merely needs to be touched slightly to control a relay that has sufficient amperage to turn the load on or off every switch has maximum current rating that should not be exceeded switch stamped 10 A at 125 V or 5 A at 2:50 V must not be used for more than 10 A at 115 V or 5 A at 2:30 V
Fuses
Any device that limits the number of amps to a predetermined flow is called an overcurrent device. The two main overcurrent devices are fuses and circuit breakers. These overcurrent devices protect the wires and the electrical device itself from overheating and overload the standard fuse that uses a short length of wire or flat metal strip are made up to 30 A when a larger fuse is needed. The cartridge fit fuse can be used up to 60 A and anything over 60 A needs a knife blade contact type fuse.
Circuit breaker
Circuit breaker opens itself and must be closed manually one single pole breaker protects a 115 V circuit one double pole breaker protects a 230 V circuit circuit. Breakers can be plug or bolt in devices that are easily replaced but they should never be replaced with a breaker of a higher rating than the wire is rated for, a breaker is made of it carefully calibrated by metallic strip when enough current flows through the strip, it tends to release a trip, and instantly interrupts the circuit circuit. Breakers are not designed to be used as a switch.
Grounds
Many appliances have a special grounding wire leading to the cold water piping system because the cold water pipe enters the building and is in contact with the ground. If not, a grounding rod is used all receptacles that are outdoors in bathrooms or supply power to feed. water appliances are required to be protected by a GFI GF eyes compare the current, leaving with the current returning to the electrical panel. Any less current is determined to be a fault, and the power is immediately disconnected.
Transformers
Lots of household things require less than 24 V a device called a transformer, decreases or transforms 115 household volts to the current that is required. The transformer consists of two windings of insulated wire on a metal core. The primary winding receives power from the 115 V supply, secondary wind in supplies proper voltage to the appliance that the transformer serves there is no metal connection between the primary and secondary winding low-voltage electrical codes, place reduced limitations on the type of wire used and the insulation on it
Electric motors
Motors up to, and including three-quarter horsepower, I referred to as fractional horsepower motors sizes, 1 hp and up are known as intra-goal, horsepower motors if you oversize a motor with a higher horsepower than needed it will run hotter than designed, because the work not taken off the shaft ends up in the heat for motor is too hot to hold with bare hands. It is either too small for the job or two enclosed to adequately dissipate it’s heat to the surrounding air.
Choosing a motor
The main drawback of electric motors is there low starting to work only after a motor has reached 75% of max speed. Does it become efficient? Small motors will have an extra winding added to the stater to give added torque until it reaches 75% of full speed at which the extra winding is disconnected when starting a motor with a medium load a capacitor start motor is preferred. The extra on this motor is a capacitor which enables the motor to start under a much heavier load, these are good up to about 6 hp in buildings first start in heavy loads the repulsion start motor is favored it draws a minimum amount of starting current and will operate on 115 or 230 V. It has brushes in other parts that have to be serviced. Periodically large electric motors can be started using a VFD or a step starter that covers for electric motors come in three designs. The first is the open drip proof housing, installed where there is clean and dry air second splashproof housing, which cost more but installed where liquids are liable to splash against the ends and three totally enclosed housing, which prevents dust and dirt from entering is also more costly, but saves on barons and motor windings.
