Chapter 2.7, 2.8, 2.9 Flashcards
drive exhaust/ ventilation fans, air handling unit blowers, refrigeration equipment
ELECTRIC MOTORS
electric motor are rated in
horsepower
at start up consumes substantially more electric power
Inrush current
the highest amperage that a motor pulls
electric motor’s locked rotor amperage
It is a fractional horsepower motor designed to operate on both AC and DC power.
Universal motor
It operates at high speeds under light load and
low speeds with a heavy load.
It can free idle at up to 20 000 rpm.
It is used on appliances such as blenders and vacuum cleaners and power tools such as routers and electric drills.
Universal motor
The motor windings are configured so that single phase AC power is split into two phases that are 1;2 out of phase. Available in sizes up to 1/3 horsepower.
This type of motor starts slowly with low torque, so it cannot begin to heavy loads.
Split-phase motor
These motors use electromagnetic induction to cause the motor rotor to turn.
Repulsion-start induction motors are capable of handling heavy starting loads.
Induction motors
This type of motor operates on single-phase AC only.
Capacitor-start motors have a capacitor that stores and discharges energy to help start the motor rotor.
Capacitor motor
_________________have one or more capacitors to help start and run the motor.
Capacitor-run motors
Large motors operate more efficiently on three-phase AC power.
A single-phase motor rated at 7112 hp draws a large amount of instantaneous current at startup (up to 200 A on a 240 V single-phase circuit).
Three phase motors
Motors above 1/4 hp are designed to operate on one of two different line voltages such as 115 V or 230 V.
Larger motors operate more efficiently on a higher line
voltage because of lower 12R losses. So, if a higher line voltage
is available, it is used.
DUAL-VOLTAGE MOTORS
a switching deice designed to start, stop, and protect the motor
provide functions such as jogging, plugging, operating at several speeds or reduced current and motor torque levels
motor controllers
a centrally located, sheet metal, a cabinet-like enclosure that houses starters and controls that control and protect several motors.
MOTOR CONTROL CENTERS (MCC)
The ___________________ contains operator controls and gauges.
front panel of an MCC
The __________________ contains plug-in units such as starters, controls, and specialized units.
interior of the MCC
a solid-state electronic power conversion device used for controlling the rotational speed of an AC electric motor
Variable Frequency Drive
occurs when a small amount of electrical current flows through the heart for 1-3 secs
Electrocution
resemble regular receptacles, but they’re so much more.
provide a permanent solution to
childhood shock caused by tampering with electrical outlets.
feature built-in safety shutters that block foreign objects from being inserted into the receptacle.
Tamper Resistance Receptacle
unintentional flow of electrical current between a power source such as a ungrounded wire and a grounded surface
Ground Fault Interruption
Occurs when electrical current leaks or escapes to the ground.
A ground fault becomes
Ground Fault Interruption
an electrical device that detects an extremely low leak (6 mA) of electrical
current (called ground faults} and acts quickly to shut off the power.
Ground Fault Circuit Interrupter
an electrical device that detects an extremely low leak (6 mA) of electrical
current (called ground faults} and acts quickly to shut off the power.
It works by comparing the amount of current going to and returning from equipment along the circuit conductors
Ground Fault Circuit Interrupter
generally used in place of standard duplex convenience outlets that are commonly found throughout the house.
Receptacle outlet type
The most often used “receptacle type” GFCI, similar to a common wall outlet, is the type with which most consumers are familiar.
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can be installed in the panelboard in buildings equipped with circuit breakers.
gives protection to the entire branch circuit.
Circuit Breaker type
frequently used in construction and outdoor settings with electric
tools mowers, trimmers,
and similar devices
It should not be used as a
permanent alternative to a regular GFCI.
Portable type
They are intended to be used when you must bring power from an unprotected outlet into a hazardous situation
Portable type
unintentional electrical discharge characterized by the low and erratic current.
Arc Fault
arcing generates high-intensity heat and expels burning particles, which can easily ignite combustible materials.
caused by loose, damaged, or corroded wires and terminals.
Current residential breakers only detect and react to power overloads, not arc faults
Arc Fault
Occur across the break of a single conductor
For example, in the case of an electrical wire cut by a nail or
screw used to mount a wall hanging.
Series Arcing Faults
Result from direct contact of two wires of opposite polarity.
Frayed/ruptured appliances or
extension cords
staples or other fasteners that pierce or
pinch insulation on construction wire and appliance or extension cords
Cracked wire or cord insulation caused by age, heat, corrosion, or bending stress
Parallel Arcing Faults
Arcs between a single conductor and ground, such as:
wire or cords that touch vibrating metal;
in appliances, wall plugs, or switches where the internal wires are not installed correctly
where connections became loose
Ground Arcing Faults
provides enhanced protection from fires resulting from arc faults.
Arc Fault Circuit Interrupter (AFCI)
It uses electronics to recognize an arc fault and interrupts the circuit when the fault
Arc Fault Circuit Interrupter (AFCI)
detects low level arc faults
Arc Fault Circuit Interrupter (AFCI)
A branch/feeder AFCI breaker with protection provided to branch-circuit wiring in the form of a circuit breaker.
Photocourtesy to pinterest.p
CIRCUIT BREAKER TYPE
An outlet AFCI for protecting connected cord sets and power supply cords in the form of an outlet receptacle.
CONVENIENCE OUTLET TYPE
portable AFCI for protecting connected cord sets and power supply cords that can be moved from outlet to outlet
Portable TYpe
cord mounted AFCI for protecting the power-supply cord connected to it (in the form of an attachment plug on a power-supply cord}.
Photocourtesy to elprocus.com
Cord Mounted TYpe
the tendency of GFCIs and AFCIs to trip frequently because both of them are extremely sensitive.
Nuisance Tripping
for this reason, it is not recommended practice to connect essential equipment and appliances that contain perishable products into an outlet with GFCI or AFCI protection.
Lightning
silent, invisible magnetic fields produced any time electricity runs through a wire, an appliance, or piece of equipment.
Extremely Low-Frequency Electromagnetic Fields
Produced by high levels of EMF.
Are visible screen jitter in video displays,
humming in telephone/audio equipme t and data errors.
Higher levels of EMF can cause comput r monitor interference and raise potenti
health concerns
Electromagnetic Interference
In the United States, EMF is measured in units called ____________
milligauss (mG)
In most of the world and in scientific community, it is measured in ___________
microtesla (µT).
Instrument used in measuring EMF radiation levels
from fans, electrical appliances, wiring, and power lines.
The most significant exposure to EMFS is from household appliances
or business equipment, not power lines in the US.
ELF (extremely low-frequency) meter
by using a conductive sheet material in front of the appliance or equipment
Passive shielding
uses a system that senses the existence of a magnetic field in the building area to be shielded.
Active shielding
designed to detect and rapidly interrupt low level equipment ground faults.
operates on the same principle as GFCI
(ground fault circuit interrupter) protection by monitoring the current drawn through the conductors of an electrical circuit and quickly shutting off power when the current is not equal.
Ground Fault Protection (GFP)
A particular type of sensing transformer. It
encircles the conductors in the switchboard
or panel board and produces a low-current
output signal if all current flowing to the
load does not return to the source through
the phase or neutral conductors.
Current Transformer (CT)
The low-current output is sensed by a
ground fault relay with adjustable
sensitivity and time delay settings. When
a signal above the sensitivity setting
persists beyond the time delay setting,
the relay operates to open the switch or
circuit breaker
Current Transformer (CT)
A sudden increase in electrical current or voltage that is very short in duration.
The said increase may be caused by a lightning strike or sudden power spike caused by a problem in the utility transmission and generating system.
May damage sensitive equipment
Power surge
A measure of the level of surge that an SPD can withstand
Surge rating
They work by instantly limiting the transient voltage from a power surge to a safe level for the equipment they protect by diverting the large surge current safely to the ground
Surge protection device (SPD)
A semiconductor device used mainly on AC power applications with surge ratings ranging from a few hundred to many thousands of amps.
METAL OXIDE VARISTOR (MOV)
A primary surge protection component with a surge rating of several thousand amps comprises a sealed tube containing a particular gas that breaks down at a given voltage rise time.
GAS DISCHARGE TUBES (GDT)
A secondary surge protection component used for ,accurate clamping of surge voltages.
It has a quicker response time than the GDTs and provides a more accurate clamping voltage than MOVs.
ZENER DIODE
A circuit comprising different types of surge protection components, taking advantage of each component’sstrengths. A hybrid may combine the high surge capability of a GDT with the accurate voltage clamping of a surge diode
HYBRID CIRCUIT
it refers to the peak instantaneous current, measured in amperes, drawn by an electrical appliance or piece of equipment
Inrush current or input surge current
An inrush current can also be reduced by an ___________________, which protects circuits that encounter high inrush loads.
inrush current limiter
Photocourtesy to watelectronics.c.om
are the most used inrush current limiter for power supplies and motors.
NEGATIVE TEMPERATURE COEFFICIENT (NTC) THERMISTORS
a thermally sensitive resistor with a resistance that changes significantly and predictably due to temperature changes.
When equipment is first turned on, the NTC thermistor is cooled, and its resistance is high, limiting current flow.
Thermistor
Resistance decreases rapidly as the thermistor self-heats, allowing near-full current to flow (at 61 0).
A disadvantage is that when the NTC thermistor is switched off, it initially retains heat, so it offers little resistance and cannot limit the inrush current until heat is dissipated.
The cooldown time varies according to the
device, its mounting method, and ambient temperature.
Thermistor
Lightning discharges have been measured from 2000 A to more than 200 000 A, with rise times to peak current of less than 10 microseconds (10 millionths of a second). As a result, lightning causes more damage, injuries, and deaths each year than tornadoes, hurricanes, or floods.
LIGHTNING PROTECTION
Lightning discharges have been measured from 2000 A to more than 200 000 A, with rise times to peak current of less than 10 microseconds (10 millionths of a second}. As a result, lightning causes more damage, injuries, and deaths each year than tornadoes, hurricanes, or floods.
LIGHTNING PROTECTION
He first suggested protecting buildings and other structures from the effects of direct lightning strikes by the use of protective conductors.
Benjamin Franklin
His theory stated that lightning protection must provide a direct path for the lightning bolt to follow to the ground, and it must prevent destruction, injury, or death as the current travels that path.
Benjamin Franklin
sometimes called air terminals, are placed at the top of the protected structure. These lightning rods have equally spaced a maximum of 20 ft, apart from the structure’s high points.
VERTICAL LIGHTNING RODS
A network of conductive copper or aluminum tape (thick, flat cable) bonds the rods to grounding electrodes driven into the earth. Metal roof vents in the proximity of the lightning rods are also connected to the conductive tape
The system of vertical rods, tape, and ground electrodes is designed to present a
VERTICAL LIGHTNING RODS
impedance (resistance) path to the lightning current that diverts current away from the building’s structural parts.
A _________________ can minimize the damaging effects of a lightning strike. Additionally, power passing through electrical circuits can generate relatively high magnetic fields that damage electronic equipment. ________ the wiring can minimize damage.
spitting facts,surge protection device, Shielding
EQUIPMENT FOR HAZARDOUS LOCATIONS
Ina hazardous location, such as a gasoline station, paint spray booth, or factory, explosion-proof or explosion resistant equipment and wiring must be used.
A _____________ is when fire or explosion hazards may exist because of flammable gases or vapors, flammable liquids, combustible dust, or quickly ignited fibers under regular operation or abnormal operating conditions.
hazardous location
Types of hazardous locations are grouped by class and division or by zone. Buildings or building spaces identified as hazardous locations must meet regulations specific to the group it falls into.
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Incontrast, explosion-resistant equipment is designed to prevent the ignition of explosive or flammable material. A Nationally Recognized Testing Laboratory (NRTL), such as UL, accomplishes testing explosion-proof or explosion-resistant equipment and wiring components.
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The _____________of an electric motor are typically listed on the ____________.
specifications, nameplate
___________ is a serious workplace hazard resulting in serious injuries and even fatalities.
Electricity
_______________only detect and react to power overloads, not arc faults.
Current Residential Breakers
A ______________ minimize the damaging effects of a lightning strike. Additionally, power passing through electrical circuits can generate relatively high ___________.
Surge Protection Device, magnetic fields.
