EMC Chapter 12 Flashcards
Originally, most knife switches were made of ___, which required replacement after repeated arcing, heat generation, and mechanical fatigue.
copper
A(n)___ was an improvement made to the original design of a knife switch.
operating spring
A ___ is a device used only periodically to remove electrical circuits from their supply source.
disconnect
Manual contactors are normally used ___.
with lighting circuits
The T-frame used with a 3phase manual contactor is activated by a ___ mechanism.
pushbutton
An advantage of ___ contacts is that the oxide (rust) that forms on the metal is an excellent conductor of electricity.
silver alloy
A(n)___ is the arrangement of contacts in such a way that both sets of contacts cannot be closed at the same time.
mechanical interlock
A ___ rotor is a condition when a motor is loaded so heavily that the motor shaft cannot turn.
locked
A motor that is starting draws a tremendous ___ current (normally six to eight times the running current) when the circuit is closed.
inrush
It is estimated that every ___degress C rise over normal ambient temperature ratings for insulation can reduce the life expectancy of a motor by almost a year.
1
A(n)___ coil converts the excess current drawn by a motor into heat, which is used to determine whether the motor is in danger.
heater
A ___ alloy is a metal that has a fixed temperature at which it changes directly from a solid to a liquid state.
eutectic
AC manual starters are selected based on phasing, voltage, starter size, enclosure type, and ___.
number of poles
A ___ V, 1 phase power source has two hot wires, L1 and L2 (ungrounded conductors), and no neutral.
230
___ action is the principal operated mechanism for magnetic contractors.
Solenoid
Two-wire control is normally used for ___ installations where an immediate return to service after a power failure is required.
remote or inaccessible
___ control provides low-voltage release and low-voltage protection.
Three-wire
AC contactor assemblies are made of laminated ___, while DC assemblies are solid.
steel
___ are used to reduce the distance required and yet quench arcs quickly.
Magnetic blowout coils
___ overload relays are extremely quick to reset because they do not require a cooling-off period before being reset.
Magnetic
A(n)___ overload relay is an overload relay that resets automatically.
bimetallic
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.
red
A ___ is used to change the amount of current flowing to a motor but reduces the current to a lower valve for the overload relay.
current transformer
If a motor has an FLC rating of 10 A with an SF of 1.15, the excess short-term current equals ___A.
11.5
Overload relay devices are normally rated to trip at a specific current when surrounded by an ambient temperature of ___degrees C.
40
For fully reliable motor protection, heat coils should be selected based on the motor ___ rating shown on the motor nameplate.
full-load current.
A(n)___ motor protector is an overload device located directly on or in a motor to provide overload protection.
inherent
A ___ is an overcurrent protection device with a mechanism that automatically opens the circuit when an overload condition or short circuit occurs.
circuit breaker
Contactor and magnetic motor starter modification devices include additional electrical contacts, power poles, pneumatic timers, transient suppression modules, and ___.
control circuit fuse holders
Additional NC contacts are used to turn on additional loads anytime a connector or starter is OFF, as well as to provide electrical ___.
interlocking
Normally, only one ___ unit with one or two contacts is added per contactor or motor starter.
power pole
Transient suppression modules normally consist of resistance/capacitance (RC) circuits and are designed to suppress the voltage transients to approximately ___% of peak coil supply voltage.
200
Loose connections in the power circuit of contactors and motor starters cause ___.
overheating
When troubleshooting a contactor or motor starter, the voltage is acceptable if the voltage reading is within ___% of the motor voltage rating.
10
___ state a problem, its possible causes, and corrective actions that may be taken.
Troubleshooting guides.
