EMC Chapter 12

Question 1

Originally, most knife switches were made of ___, which required replacement after repeated arcing, heat generation, and mechanical fatigue.

Answer 1

copper

Question 2

A(n)___ was an improvement made to the original design of a knife switch.

Answer 2

operating spring

Question 3

A ___ is a device used only periodically to remove electrical circuits from their supply source.

Answer 3

disconnect

Question 4

Manual contactors are normally used ___.

Answer 4

with lighting circuits

Question 5

The T-frame used with a 3phase manual contactor is activated by a ___ mechanism.

Answer 5

pushbutton

Question 6

An advantage of ___ contacts is that the oxide (rust) that forms on the metal is an excellent conductor of electricity.

Answer 6

silver alloy

Question 7

A(n)___ is the arrangement of contacts in such a way that both sets of contacts cannot be closed at the same time.

Answer 7

mechanical interlock

Question 8

A ___ rotor is a condition when a motor is loaded so heavily that the motor shaft cannot turn.

Answer 8

locked

Question 9

A motor that is starting draws a tremendous ___ current (normally six to eight times the running current) when the circuit is closed.

Answer 9

inrush

Question 10

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.

Answer 10

1

Question 11

A(n)___ coil converts the excess current drawn by a motor into heat, which is used to determine whether the motor is in danger.

Answer 11

heater

Question 12

A ___ alloy is a metal that has a fixed temperature at which it changes directly from a solid to a liquid state.

Answer 12

eutectic

Question 13

AC manual starters are selected based on phasing, voltage, starter size, enclosure type, and ___.

Answer 13

number of poles

Question 14

A ___ V, 1 phase power source has two hot wires, L1 and L2 (ungrounded conductors), and no neutral.

Answer 14

230

Question 15

___ action is the principal operated mechanism for magnetic contractors.

Answer 15

Solenoid

Question 16

Two-wire control is normally used for ___ installations where an immediate return to service after a power failure is required.

Answer 16

remote or inaccessible

Question 17

___ control provides low-voltage release and low-voltage protection.

Answer 17

Three-wire

Question 18

AC contactor assemblies are made of laminated ___, while DC assemblies are solid.

Answer 18

steel

Question 19

___ are used to reduce the distance required and yet quench arcs quickly.

Answer 19

Magnetic blowout coils

Question 20

___ overload relays are extremely quick to reset because they do not require a cooling-off period before being reset.

Answer 20

Magnetic

Question 21

A(n)___ overload relay is an overload relay that resets automatically.

Answer 21

bimetallic

Question 22

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.

Answer 22

red

Question 23

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.

Answer 23

current transformer

Question 24

If a motor has an FLC rating of 10 A with an SF of 1.15, the excess short-term current equals ___A.

Answer 24

11.5

Question 25

Overload relay devices are normally rated to trip at a specific current when surrounded by an ambient temperature of ___degrees C.

Answer 25

40

Question 26

For fully reliable motor protection, heat coils should be selected based on the motor ___ rating shown on the motor nameplate.

Answer 26

full-load current.

Question 27

A(n)___ motor protector is an overload device located directly on or in a motor to provide overload protection.

Answer 27

inherent

Question 28

A ___ is an overcurrent protection device with a mechanism that automatically opens the circuit when an overload condition or short circuit occurs.

Answer 28

circuit breaker

Question 29

Contactor and magnetic motor starter modification devices include additional electrical contacts, power poles, pneumatic timers, transient suppression modules, and ___.

Answer 29

control circuit fuse holders

Question 30

Additional NC contacts are used to turn on additional loads anytime a connector or starter is OFF, as well as to provide electrical ___.

Answer 30

interlocking

Question 31

Normally, only one ___ unit with one or two contacts is added per contactor or motor starter.

Answer 31

power pole

Question 32

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.

Answer 32

200

Question 33

Loose connections in the power circuit of contactors and motor starters cause ___.

Answer 33

overheating

Question 34

When troubleshooting a contactor or motor starter, the voltage is acceptable if the voltage reading is within ___% of the motor voltage rating.

Answer 34

10

Question 35

___ state a problem, its possible causes, and corrective actions that may be taken.

Answer 35

Troubleshooting guides.