Chapter 15: Reversing Motors

How is a DC permanent-magnet motor wired to the starter?

A2 is positive and A1 is negative for forward and vice versa for reverse.

What diagram is used to properly wire a DC compound motor for reversing?

Wiring Diagram

What diagram is used to properly wire a DC permanent-magnet motor for reversing?

Wiring Diagram

What diagram is used to properly wire a DC series motor for reversing?

Wiring Diagram

What diagram is used to properly wire a DC shunt motor for reversing?

Wiring Diagram

What two circuits are required when using motor starters or motor drives?

a power circuit and a control circuit

Reversal of a DC compound motor is accomplished by reversing the ___ connections only.

armature

The direction of rotation may be reversed in a DC motor by reversing the direction of the current through the armature without changing the direction of the current through the ___.

fields

Drum switches are totally enclosed and a(n) ___ provides the means for moving the contacts from point to point.

insulated handle

How do you reverse a single-phase motor?

interchanging the leads of the starting or running windings.

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

interlock

A ___ circuit allows the operator to start a motor for short times without memory.

jogging

If several connections of a given number are required, ___ can be added to the terminal strip to provide multiple connection points to one given terminal number.

jumpers

A drum switch is used only as a means of controlling the direction of a motor by switching the ___ of the motor.

leads

In a DC compound motor, the series and shunt field relationship to the armature must be _________

left unchanged. the shunt field and the series field must be connected in series with the armature.

A ___ is used to illustrate circuit logic.

line diagram

What are the differences between manual and magnetic reversing starters?

magnetic reversing starters have the addition of forward and reverse coils and the use of auxiliary contacts.

What two ways does a drum switches contacts come in?

maintained contacts or spring return contacts

A ___ starter is a contactor with an added overload protective device.

manual

What can be used to reverse the direction of current flow through the armature of all DC motors?

manual starter

How do you determine the leads of a single phase motor if a manufacturer's wiring diagram is not available?

measure the resistance of the starting winding and running winding to determine which leads are connected to which windings.

A(n) ___ interlock is normally factory-installed by the manufacturer.

mechanical

To reverse a running motor using a drum switch, the handle must first be moved to the center position until the motor ___ and then moved to the reverse position.

stops

How many manual starters are connected together to create a manual reversing starter?

two

When is a drum switch usually used?

where an operator's eyes must remain on a particular operation such as when a crane is raising and lowering a load

A ___ diagram is used to locate the actual test points at which a DMM is connected to the circuit.

wiring

Always consult the manufacturer ___ to ensure proper wiring.

wiring diagram

How is a DC compound motor wired to the starter?

A2 is positive and A1 is negative for forward and vice versa for reverse. F1 is always negative and F2 and S2 are always positive.

How is a DC shunt motor wired to the starter?

A2 is positive and A1 is negative for forward and vice versa for reverse. F1 is always negative and F2 is always positive.

How is a DC series motor wired to the starter?

A2 is positive and A1 is negative for forward and vice versa for reverse. S1 is always negative and S2 is always positive.

___ lines are used between the manual starters in a wiring diagram to indicate a mechanical interlock.

Crossing dashed

What is the oldest and most straightforward motor control wiring method used?

Direct Hardwiring

In a DC shunt motor, regardless of whether the forward contacts or reverse contacts are closed, ___ is always positive.

F2

Although any two lines may be interchanged to reverse a 3Φ motor, the industry standard is to interchange L1 and ___.

L3

___ switches may be used to provide automatic control of reversing circuits.

Limit

What is the first step to troubleshooting reversing power circuits?

Measure the incoming voltage between each pair of power leads. Incoming voltage must be within 10% of the voltage rating of the motor. Measure the voltage at the main power panel feeding the control cabinet if no voltage is present or if the voltage is not at the correct level.

What is the first step to troubleshooting reversing control circuits?

Measure the supply voltage of the control circuit by connecting a DMM set to measure voltage between line 1 (hot conductor) and line 2 (neutral conductor). Test the power circuit if the voltage is not correct. The control circuit voltage rating is determined by the voltage rating of the loads used in the control circuit (motor starter coils, etc.).

What is the fourth step to troubleshooting reversing power circuits?

Measure the voltage at the motor terminals. The voltage must be within 10% of the motor rating and equal on each power line. There is a problem with the motor or mechanical connection if the voltage is correct and the motor does not operate.

What is the third step to troubleshooting reversing control circuits?

Measure the voltage into and out of the control switch or contacts. NC switches (stop pushbuttons, etc.) should have a voltage output before they are activated. NO switches (start pushbuttons, memory contacts, etc.) should have a voltage output only after they are activated.

What is the third step to troubleshooting reversing power circuits?

Measure the voltage our of the motor starter. The voltage should be present when either the forward power contacts or reverse power contacts are closed. The contacts can be closed manually at most motor starters if the power contacts cannot be closed by using the control circuit push buttons. Disconnect the incoming power and check the motor starter contacts for burning or wear if the voltage is not at the correct level.

What is the second step to troubleshooting reversing power circuits?

Measure the voltage out of each fuse or circuit breaker. The fuse or circuit breaker is open if no voltage reading is obtained. Replace any blown fuse or tripped circuit breaker.

What is the second step to troubleshooting reversing control circuits?

Measure the voltage out of the overload contacts to ensure the contacts are closed. The contacts are tripped or faulty if no voltage is present. Reset the overloads if they are tripped. Overloads are installed to protect the motor during operation. The control circuit does not operate when the overloads are tripped.

___ wiring is wiring in which each component in a circuit is connected (wired) directly to the next component as specified on the wiring and line diagrams.

Point-to-point

___ windings are made of a heavier gauge wire than starting windings, so they have a much lower resistance than starting windings.

Running

How do you tell which windings resistance you are reading when trying to find the leads of a single phase motor?

Running windings have much heavier gauge wire making them having much less resistance then the starting windings which have much smaller gauge of wire.

How do you reverse a three-phase motor?

Swap the L1 and L3 power lines

Some DC motors have _____________ that are used to prevent sparking at the brushes in the motor.

commutating windings (interpoles)

A ___ circuit does not operate when the overloads are tripped.

control

The ___ circuit includes the required circuit inputs (pushbuttons, limit switches, etc.), motor starter coils, motor starter auxiliary contacts, overload contacts, timers, and counters.

control

The disadvantage of a(n) ___ circuit is that circuit troubleshooting and circuit modification are time consuming.

direct hardwired

A _________ is a manual switch made up of moving contacts mounted on an insulated rotating shaft

drum switch

A _________ is used only as a means of controlling the direction of a motor by switching the leads of the motor.

drum switch

Although most magnetic reversing starters provide mechanical interlock protection, some circuits are provided with a secondary backup or safety backup system that uses auxiliary contacts to provide ___ interlocking.

electrical

In direct hardwiring, the power circuit and the control circuit are wired ___.

point-to-point

Troubleshooting reversing ___ circuits normally involves determining the point in the system where power is lost.

power

Drum switches are not motor starters because they do not contain ___.

protective overloads

What is the only way to reverse a DC compound motor?

reversing the armature connections only

How do you reverse a DC permanent-magnet motor?

reversing the direction of the current through the armature

Reversing the rotation of 1Φ motors is accomplished by interchanging the leads of the starting or ___ windings.

running

A(n) ___ switch and a basic start/stop station can be used to reverse a motor.

selector

How do you reverse a DC compound motor if the motor has commutating pole windings as well?

these windings are considered a part of the armature circuit and the current through them must be reversed when the current through the armature is reversed.

Although the power circuit and control circuit operate together to control a motor, they are electrically isolated from each other through a(n) ___.

transformer