study guide 2
They are usually controlled by how many push buttons which are what
3 Forward, Reverse, and Emergency Stop
WARM POSITION BALANCED OVERCURRENT what side of the bimetals and operators on what is the % of the tripping current
3 bi-metals and the operators move to the left trips the overcurrent relay. Tripping current is 125%
three main contacts for a contactor and relay
Fixed contact Movable contact Sometimes an arc blow-out device
Direct-On-Line Reversing 70-74 what is used when it is desired to reverse the direction of rotation of a three-phase squirrel-cage motor.
Motor Starters
Coil: 55-58 The coil does what to the magnetic flux which is the result of current flow
Produces
what Laboratories evaluates fuses under specific conditions, regulatory codes and other standards including international standards?
Underwriter's Laboratories
fuses classes Safety/Standards Organizations assigns what
assign classifications to fuses based on the criteria of safety and performance.
Contactor and Relay purpose of contactor and relays
automatic operation of a machine from a remote location.
RETURN SPRING This spring insures that the moveable core rapidly moves _________ from for the stationary core when the coil is de-energized. This rapid opening insures that the contacts, both main and auxiliary ______ as quickly as possible.
away open
dual fuses overload circuit Overload Operation - On a low overload current the short circuit fuse link remains entirely (inactive,together, or none) The overload element consists of a center mass of copper on which is mounted a spring and a short connector. This connector is held in place by a low melting point solder joint, which connects the center mass of copper to the fuse link. When overload current flows long enough to _______ the temperature of the center mass to the melting point of the solder, this connector is pulled out of place by the spring, thereby opening the circuit.
inactive raise
OPERATING PRINCIPLES OF FUSES increase what
increased fuse element temperature caused by an overcurrent flowing through them Fuses remain safe and accurate since age does not increase their current carrying capacity nor lengthen their opening time. After a fuse has been used to clear a short-circuit or overload, it is replaced by a new safe, factory calibrated unit, as accurate and dependable as the original.
The magnetic coil provides what kind of trip on high or short circuit currents
instant
CASE or HOUSING is used for what
insulation necessary to isolate individual contacts.
A circuit breaker (CB) will automatically do what to the current flow when the conditions are abnormal without damage o itself and current at a particular overload value and it can interrupt a short circuit current.
interrupt
Is Continuous Current Rating the fuse intended to normally carry
is the current the fuse is intended to normally carry. true
By opening quickly, the instantaneous peak short circuit current is li__________ to a value much less than the peak that would otherwise occur.
limited
The moveable core concentrates magnetic flux radiating from the what of the stationary core.
mating surfaces
Interrupting Rating National Electric Code, Section 110-9 typical short circuit current rating
max short circuit current that a fuse can safely interrupt without rupturing interrupting rating sufficient for the current that must be interrupted available from a 500KVA, 480 Volt transformer is approximately 50,000 amperes.
Voltage Rating is what
maximum circuit voltage in which the fuse can be safely applied. The fuse also may not safely clear the fault. For instance, a 250volt fuse could safely be used in a 208volt system but not in a 480volt system.
dual fuses short circuit During a short circuit condition the fuse link vaporizes the surrounding filler aids in extinguishing the arc. This fuse element has current-limiting ability for short circuit currents thereby reducing what three things
mechanical, thermal, and arching
single fuses Short Circuit Operation On a short circuit several sections of the link _____-instantly. Arcing across the vaporized portions of the link commences, and the arc extinguishing filler quickly aids in quenching these arcs, and thus clearing the circuit. ---- Although the fuse opening operation is caused by an ______ in the link temperature, the fusing opening operation is safely contained in the fuse casing and the circuit is interrupted in a fraction of a second. The total operating time of current limiting fuses during short circuit conditions can be less than a ______- cycle (less than 8/1000 of a second). ---- For high short circuit currents the total clearing time can be _____ than a quarter cycle. It is this fast clearing speed which enables current limiting fuses to protect system components from damage due to high short circuit currents that may occur.
melt increase half less
Single fuses Overload Operation - If an overload current is more than the current and is left running for a sufficiently long period of time, the fuse link will what which can cause an ___________ across the resulting gap burns back the metal, lengthening the gap. The arc is quenched and the circuit is _________ when the break is of sufficient length. The surrounding filler aids the arc quenching process.
melts arc interrupted
this core's surface, which mates with what kind of core, is polarized and attracts the core
moveable
The mating surfaces of the moveable core are attracted to the stationary core resulting in the what of the moveable core against the stationary core.
movement
Magnetic Circuit Breaker does a magnetic circuit breaker have a thermal device magnetic breaker is used whenever instant action is ____________ to open a faulted circuit.
no required
which This does _______ trip the breaker. The breaker trips only when the excessive c__________ through the overload strip causes it to bend more than the compensating strip. The ambient-compensated circuit breaker is used in areas where _________ temperatures are encountered
not current high
what are the 2 differrent type of contacts
open and close same time as the main contact
When the moveable part of the magnetic circuit is pulled against the return spring, the moveable part of the contacts either op________ or cl__________ relative to the stationary set of corresponding contacts. This is a mechanical representation of the contactor.
open or closes
how many cycles does it take for Current Limitation to work
operates quickly in less than one half of a cycle.
CIRCUIT BREAKERS The function of the circuit breaker corresponds basically to that of a switch in combination with a fuse. When the current is above the normal rating, either on overload or short circuit current, the circuit breaker is an automatic ______________ protective device.
overcurrent An example of this is motor control systems. Circuit breakers would also be used if sufficient space is available and if standard current ratings are required, such as, 20 A, 30A etc. Fuses would be used in preference to circuit breakers where accurate current values are required, such as, 1.6A, 10.4A. Fuses (Rectifier/semi-conductor) would also be used in rapid response situations such as electronic circuits or Silicon Controlled Rectifier (SCR) Circuits found in D.C. Drives and other precise control circuits. Fuses are normally used when no disconnect means is required.
Ambient Compensating Circuit Breaker The ambient-compensated circuit breaker has an what two type of bimetallic strip.
overload and compensating bimetallic strip.
The moveable core is attached through what 2 things to the contacts.
plastic or insulated assembly
Thermal Circuit Breakers Thermal (heat) type air circuit breakers are used primarily for ______________ against overcurrent. A typical thermal circuit breaker operates on the principle of metal expanding when heated. The bimetallic strip, having resistance, heats in proportion to the line current. If the current becomes excessive for a prolonged period of time, the bimetallic strip becomes ______ and bends because of different expansion rates of the two metals as When the strip bends sufficiently, it trips the _________ and opens the contacts Thermal circuit breakers provide overload protection at voltages up to _________ volts A-C and _______ volts D-C, from 10 to 60 amperes.
protection hot latch 600 250
The magnetic trip also does what for the bimetallic strip from excessive overheating that can destroy it.
protects
THE DIGITAL MULTI-METER (DMM)
replaced the analog-type multi meter by being easier to read and more accuracy performs all standard VOM measurement functions of a-c and d-c
The connections of one contactors does what to the supply voltage to two of the three motor terminals.
reverses
A contactor belongs to both control circuit and the power circuit by which two things
seal-in or provide electrical interlock
two basic types of current-limiting fuses
single and dual element
Semiconductor or Rectifier type is what kind of applications
special applications on electronic equipment such as power supplies. very fast acting and are sized just like the single element type used for a control transformer secondary.
As the moveable core is pulled against the stationary core, the contacts change what
state
The electromagnet is ultimately responsible for doing what to the state of the contacts.
switching
Measuring voltage
1. Select volts AC (V~), volts DC (V---), mvolts (V---) as desired 2. Plug the black test lead into the COM jack and the red test lead into the V jack 3. Touch the probe tips to the circuit across a load or power source as shown (parallel to the circuit to be tested) 4. View the reading being sure to note the unit of measure Note: For DC readings of the correct polarity (+ or -), touch the red test probe to the positive side of the circuit, and the black test probe to the negative side of the circuit ground. If you reverse the connections, a DMM with auto-polarity will merely display a minus sign indicating negative polarity. With an analog meter you risk damaging the meter.
Measuring resistance
1. Turn off power to the circuit 2. Select resistance 3. Plug the black test lead into the COM jack and the red test lead into the ohms jack 4. Connect the probe tips across the component or portion of the circuit for which you want to determine the resistance 5. View the reading and be sure to note the unit of measure, , K, M, etc. ohms
Measuring current
1. Turn off the power to the circuit 2. Disconnect, cut or unsolder the circuit 3. Select amps AC (A~), or amps DC (A---) as desired 4. Plug the black test lead into the COM jack and the red test lead into 10 amp (10A) or 300 milliamp (300mA) jack depending on the expected value of the reading 5. Connect the probe tips to the circuit across the bread as shown so that all current will flow through the meter (a series connection) 6. Turn the circuit power back on 7. View the reading being sure to note the unit of measure Note: If test leads are reversed a negative (-) sign will be displayed The measurement of current is rarely performed when troubleshooting, as the circuit path has to be opened to insert the DMM in series with the current flow. However, if current is to be measured, the red lead is inserted into one of the ampere jacks, 10 amp (10A) or 300 milliamp (300 mA) input jack depending on the expected value of the reading.
Short Circuit is how many times greater than the normal current level short circuit can great enough to produce what which can result in what
100x times greater than normal current levels The heat energy produced by a short circuit current can be great enough to vaporize metal, melt conductors, and cause severe insulation damage. Arcing produces ionized gases Short circuit currents can result in destroying cable trays, warping bus bars and completely disconnecting the bus bars from their retaining supports.
The standard arrangement consists of a set of #'s of poles which are what
2,3 poles contactors operated electro-magnetically and mechanically linked together.
Since the moveable core is made to move, it is often referred to as the what This core is also constructed of laminated steel to reduce what current
Armature eddy
Forward-Reverse Contactor with Limit Switches controls what
Control Stopping of the Opposing motions
curcuit breaker disadvantages
Cost - Size - Handling and Weight when disconnect is required
Only the what resistance of the coil limits the current in a DC circuit.
DC
where would the Selective Coordination occur or open
If distribution systems protective devices are selective, only the protective device nearest the faulted circuit will open maintained between upstream and downstream continuous current ratings. The ratio is specified by the fuse manufacturer and depends on the type of fuse.
The coil's impedance is mainly what kind of reactance since the coil usually has a very low internal resistance.
Inductive
Class Types To overcome this problem a feature is built into the end ferrules of class RK1 and RK5 fuses. The "R" in the class designation indicates a rejection type fuse with a minimum interrupting rating of ___#____ amperes. Rejection type fuses will fit only into what kind of blocks The fuse block rejects what class fuse
K5 fuse rating of 50,000 to 200,000 amperes class H fuse has a rating of 10,000 amperes. rejection feature 200,000 fuse block H
what are three fuses classes underwriter laboratories might put a fuse in
Rk1 h J
WARM POSITION NORMAL BALANCED CURRENT what side are the bimetals and operators on
The 3 bi-metals and the operators move to the left the same distance d.
Over current relay DIFFERENTIAL Operation COLD POSITION what side are the bimetals and operator on
The differential operators are hard over to the right
Fuses purpose is to prevent what what does it minimize the damage on
a fault that prevent damage to equipment. components such as conductors, transformers, motors, motor starters, etc.
what is the U.L. Classifications for Low Voltage Fuses rating
a fuse with a voltage rating of 600 volts or less.
SINGLE ELEMENT FUSES
a link or several links contained in a tube filled with arc-quenching filler
Both elements ___________ with an increase in ambient heat but only the ______________ element responds to the current. Figure A illustrates the ambient compensating circuit breaker in a normal ambient temperature of _____ to ______- degrees C.
bend overload 18-21
Curcuit breaker advantages
breakers being reset used as switching devices adjustable
WARM POSITION UNBALANCED CURRENT what is the bimetals and operators on what is the % of the tripping current
causes unequal deflection of the 3 bi-metal strips. The tripping current is 80%
look at sheet Both contain a c________ that has terminal numbers ________ The contactor has three main contacts numbered _______________ which are designed to carry he______________ to motors, heaters, etc. The darker lines show these main contacts. The contactors ____________ contacts are shown with smaller lines and numbered 13 - 14. The ______ has all smaller auxiliary type contacts with different numbers. look at sheet
coil A1 and A2. L1 -T1, L2 - T2, L3 - T3, heavy loads auxiliary 13 - 14 relay 43-44
The electromagnet consists of the following:
coil, moveable and stationary core
Stationary Core: 59-61 The stationary core does what with magnetic flux
concentrates
The Moveable Core 62-68 The moveable core also does what to magnetic flux
concentrates
A relay is always used in the what circuit
control
This core is constructed of laminated steel to reduce what currents.
eddy
ELECTROMAGNET 52-54 The main feature of a contactor that distinguishes it from a manual starter is the use of an what
electromagnet
Overcurrent excess current from what
excess current from a short circuit or an overload.
Overload is excess current from what
excess current from the normal current one to six times the normal current. becomes harmful only when it is sustained.
Auxiliary contacts does what for a contactor and relay
fixed contact Movable contact
.The what of the coil limits the current in an AC circuit.
impedance
Dual element fuses The th__________ cutout gives dual element fuses a time delay on overloads, such as motor starting current. This d_________ allows the motor starting current to be disregarded during that time as long as the current is within five to ________ times normal running current. The f_______ link in dual element fuses provides current limiting, short circuit protection just as single element fuses. two fusible elements which are The magnitude of the o___c_______ determines which element functions. The thermal cutout element is designed to o_______ on overcurrents of up to approximately 500% of the fuse ampere rating. The fuse link or short circuit element is designed to o________ on heavier overloads and short circuit currents.
thermal delay 6 fuse thermal cutout and fuse link overcurrent open open The thermal cutout element has a built-in time delay which permits momentary harmless surge currents such as motor starting current to flow without opening the fuse. If the overload current persists too long, the thermal cutout element clears the circuit, thus protecting the components and equipment. These fuses are ideal for motor, transformer and other circuits with harmless start-up current.
The automatic circuit opening action of a circuit breaker is accomplished in several ways. which are
thermal release, magnetic action, the combination of thermal release and magnetic actions, hydraulic means, and pneumatic means.
Thermal-Magnetic Circuit Breaker A thermal-magnetic circuit breaker incorporates both a _______ strip and a _________ coil.
thermal strip and a magnetic coil.
The thermal strip provides a what delay for momentary overloads.
time
