Ch 12 Test: Contactors and Magnetic Motor Starters
magnetic motor starter
Electronically operated switch (contactor) that includes motor overload protection
AC contactors
Which contractors assemblies are made from laminated steel?
To protect against inrush current, the dangerously high current of a shorted circuit or ground fault
Why must a motor be protected by an overload relay
One
It is estimated that every ___ degree celcius rise over normal ambient temperature ratings for insulation can reduce the life expectancy of a motor by almost year.
overload protection
What is a disconnect (safety switch) used for
230
A ___ V , 10 power has two hot wires, L1 L2 (ungrounded conductors ) , and no neutral.
heater
A ___ coil converts the excess current drawn by a motor into heat, which is used to determine whether the motor is in danger
circuit breaker
A ____ is an overcurrent protection device with a mechanism that automatically opens the circuit when an overload condition or short circuit occurs
mechanical interlock
A ____ is the arrangement of contacts in such a way that both sets of contacts cannot be closed at the same time.
current transformer
A ____ is used to change the amount of current flowing to a motor but reduces the current to a lower value for the overload relay
bimetallic
A ____ overload relay is an overload relay that resets automatically
locked
A ____ rotor is a condition when a motor is loaded so heavily that the motor shaft cannot turn.
Arc chute
A device that confines, divides and extinguishes arc draws between contacts opened under load
Higher
A double break contact has a ____ contact rating than a single break contact in a small place
inrush
A motor that is starting draws a tremendous ____ current (normally six to eight times the running current) when the circuit is closed
steel
AC contactor assemblies are made of laminated ___ while DC assemblies are solid.
number of poles
AC manual starters are selected based on phasing, voltage, starter size, enclosure type, and____.
disconnect
A____is a device used only periodically to remove electrical circuits from their supply source.
interlocking
Additional NC contacts are used to turn on additional loads anytime a contactor or starter is OFF, as well as to provide electrical _____
eutectic
An ____ alloy is a metal that has a fixed temperature at which it changes directly from a solid to a liquid state
inherent
An ____ motor protector is an overload device located directly on or in a motor to provide overload protection
operating spring
An ____was an improvement made to the original design of knife switch .
silver alloy
An advantage of ____ contacts is that the oxide (rust) that forms on the metal is an excellent conductor of electricity
less
As ambient temperature increases ___ current is needed to trip the overload devices
control circuit fuse holders
Contactor and magnetic motor starter modification devices include additional electrical contacts, power poles, pneumatic timers, transient suppression modules and ____
Double break contactors
Contactors that break the electrical circuit in two places
full-load current
For fully reliable motor protection, heat coils should be selected based the motor ____ rating shown on the motor nameplate.
AC: all three, DC: only one
How many phases should be broken in a three phase load
11.5
If a motor has an FLC rating of 10 A with an SF of 1.15, the excess short-term current equals ___ A.
overheating
Loose connections in the power circuit of contactors and motor starters cause ____
lighting circuits
Manual contactors are normally used with ____
Service factor rating
Number designated that represents the percentage of extra demand that can be placed on a motor for short intervals without damaging the motor
power pole
Normally, only one ____ unit with one or two contacts is added per contactor or motor starter.
copper
Originally, most knife switches were made of _ which required replacement after repeated arcing, heat generation, and mechanical fatigue.
40
Overload relay devices are normally rated to trip at a specific current when surrounded by an ambient temperature of ____ degrees Celsius
pushbutton
The T - frame contactor is activated by a ____mechanism .
red
The ____ indicator on a trip indicator informs the operator or electrician why the unit is not operating and that it is potentially capable of restarting with an automatic reset.
Service factor rating
The number designation that represents the percentage of extra demand that can be placed on a motor for short intervals without damaging the motor
Full load current rating, service factor, ambient temperature
Three general factors that must be considered when selecting overloads
200
Transient suppression modules normally consist of resistance/capacitance (RC) circuits designed to suppress the voltage transients to approximately ____ percent peak coil supply voltage.
remote or inaccessible
Two-wire control is normally used for ____ installations where an immediate return to service after a power failure is required.
10
When troubleshooting a contactor or motor starter, the voltage is acceptable if the voltage reading is within ____ percent of the motor voltage rating
Three-wire
____ control provides low-voltage release and low-voltage protection.
Magnetic
____ overload relays are extremely quick to reset because they do not require a cooling-off period before being reset.
Solenoid
_____ action is the principal operating mechanism for magnetic contactors
Magnetic blowout coils
_____ are used to reduce the distance required and yet quench arcs quickly
Magnetic
_____ overload relays are extremely quick to reset because they do not require a cooling-off period before being reset.
Troubleshooting guides
_____ state a problem, its possible causes, and corrective actions that may be taken.