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.