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
