ELT Machinery and Control Quiz 4

It is almost never desirable to have more than one start-stop push-button station to control a motor.

False

When a component is used to perform the function of stop in a control circuit, it will generally be a normally ____ component and be connected in ____ with the motor starter coil.

Closed series

Some control components, such as limit switches, photodetectors, or flow switches, may be located on the machine itself, while other components such as control relays and motor starters may be located inside a cabinet.

True

____________________ prevents some action from taking place until some other action has been performed.

Interlocking

A(n) ____________________ switch can be employed to provide jogging. The switch is used to break the connection to the holding contacts.

Selector

Because the motor is connected to the power line regardless of which direction it operates, ____ contactor(s) is (are) needed for each direction.

Separate

Inching control requires the use of ____ contactor, because the power supplied to the motor must be different from full line voltage.

Separate

A(n) ____________________ box indicates terminal numbers for the relay and these numbers should not be confused with wire numbers.

Square

What is the primary difference between the point-to-point and terminal strip methods?

The primary difference between the two methods is that wires from the different components are brought to the terminal strip and connection is made at that location

How can you reverse the direction of rotation of a single-phase split-phase motor?

To reverse the direction of rotation of a single-phase split-phase motor, either the starting winding leads or running winding leads, but not both, are interchanged.

___________________ can be used to reduce the amount of voltage applied to the motor during inching, or reactors or resistors can be connected in series with the motor to reduce the current supplied by the power line.

Transformers

Notation is generally used to help the electrician interpret the meaning of certain components and find contacts that are controlled by coils.

True

Schematics in industry are often complicated and may contain several pages.

True

Terminal strips are used as connection points between the control wiring inside the cabinet and inputs or outputs to the machine or control panel.

True

The direction of rotation of any three-phase motor can be reversed by changing any two motor T leads.

True

Hand-off-automatic controls are used to prevent an operator from selecting between automatic or manual operation of a motor.

False

How do jogging circuits work?

As with many other types of control circuits, there are different ways in which jogging can be accomplished but, basically, jogging is accomplished by preventing the holding contact from sealing the circuit around the start push button when the motor starter energizes. It should also be noted that jogging circuits require special motor starters rated for jogging duty.

True reversing controllers contain two separate contactors and _____ overload relay(s).

One

When a component is used to perform the function of start, it is generally normally ____________________.

Open

When a component is used to perform the function of start, it is generally connected in ____________________ with the existing start button.

Parallel

In the point-to-point method, components are connected from one point to another depending on the ____________________ of one component to another.

Proximity

A ____ switch permits power to be supplied to the circuit or not.

Stop-run

What letter indicates a connection between terminals?

X

If only one motor is in operation, only one overload relay is needed to protect the motor.

True

The addition of a(n) ____ to the jog circuit eliminates the problem of the holding contacts making connection before the normally closed section of the jog push button reconnects.

Control relay

A(n) ____________________ line indicates that two switches are mechanically connected.

Dashed

In the schematic, the connections made inside the MCC are shown with ____ lines.

Dashed

The term inching actually means to start a motor with short jabs of power at full voltage.

False

The term jogging means to start a motor with short jabs of power at reduced voltage.

False

Most reversing controllers contain ____________________ interlocks as well as electrical interlocks.

Mechanical

The notation (2300V 3 60 Hz) means that the motor is

Three Phase

After wire numbers are placed on the schematic, corresponding numbers are placed on the control components.

True

Most control schematics are numbered to aid the electrician in troubleshooting.

True

Why is practice important for reading schematic diagrams?

The old saying "Practice makes perfect" certainly applies to reading schematic diagrams. Although there are notations that are common to many industrial control schematics, nothing is standard. Many manufacturers use their own numbering and notation system, specific to their company. Some use the NEMA symbols that are discussed in this text and others do not. With practice and an understanding of basic control logic and schematics, most electricians can determine what these different symbols mean and the way they are used in a circuit.

A flow switch can be used to detect the flow of water to ensure that a fan motor cannot run if there is no flow of cooling water.

True

What is the advantage of connecting components to a terminal strip?

Although connecting components to a terminal strip generally involves using a greater amount of wire, it can be the less expensive method when it is necessary to troubleshoot the circuit. If the electrician needs to know if the normally open switch on float switch FS1 is open or closed, he or she can test it from the terminal strip without having to find FS1, remove the cover, and check the condition of the contacts.

Consider a circuit needing a flow switch with two separate contacts, one normally open and the other normally closed. When one switch changes position, the other switch changes position. What happens if a flow switch with two separate switches cannot be obtained?

If a flow switch with two separate switches cannot be obtained, it is possible to use a single-pole double-throw switch with a common terminal, a normally open terminal, and a normally closed terminal.

Current transformers produce an output current of 5 amperes under

Short Circuit

One terminal of both a normally open switch and normally closed switch are connected together. This forms a common point for both switches and could be used as the common terminal for a flow switch that contains a ____ switch.

Single pole double throw

When the HOA switch is placed in the Auto position, a(n) ____ controls the action of the fan.

Thermostat

What is the meaning of the notation (200A 5000V DISCONNECT SWITCH)?

This notation indicates that there is a 200-ampere disconnect switch, rated at 5,000 volts, that can be used to disconnect the motor from the power line.

What are the two methods of electrical interlocking?

Two methods of electrical interlocking are available. One method is accomplished with the use of double-acting push buttons. The second method of electrical interlocking is accomplished by connecting the normally closed auxiliary contacts on one contactor in series with the coil of the other contactor.

A(n) ____________________ lamp indicates that there is no flow of water when the circuit is energized.

Warning

____________________ diagrams can be misleading in that they show all components grouped together.

Wiring

Discuss the differences in the numbering of schematics.

Although most control schematics are numbered to aid the electrician in troubleshooting, several methods are used. Regardless of the method used, all numbering systems use the same principles. An electrician who learns this method of numbering a schematic will have little difficulty understanding a different method.

Why are the terms jogging and inching often used interchangeably?

Although the two terms mean different things, they are often used interchangeably because both are accomplished by preventing the holding contacts from sealing the circuit.

When M coil energizes, all M contacts ____.

Change position

When the M coil energizes, what happens to the normally open auxiliary contact?

When the M coil energizes, the normally open auxiliary contact connected in parallel with the two Start buttons closes to maintain the circuit to M coil when the Start button is released.

When the M coil energizes, what happens to the load contacts?

When the M coil energizes, the three load contacts connected between the three-phase power line and the motor close to connect the motor to the line.

What happens when the hand-off-automatic switch is set in the Hand position?

When the hand-off-automatic switch is set in the Hand position, connection is made between terminals 1 and 2. This permits the motor to be controlled by a start-stop push-button station. In this mode, the fan will run continuously until the Stop button is pressed.