MOTORS MOTORS MOTORS B55a > Chapter 8 > Flashcards

Chapter 8 Flashcards

(43 cards)

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1
Q
  1. The magnetic contactor is similar in operation to the electromechanical

_________________________ .

  1. Contactors are designed to make and break electric circuit loads of higher currents than relays.___________________ (True or False)
A

relay

true

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2
Q

Identify the components of the contactor shown in Figure 6-1.

a) ________________________________
b) ________________________________
c) ________________________________

A

coil

power contacts

auxiallry contact

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3
Q
  1. The coil is part a magnetic contactor’s ______________________ circuit.
  2. The contacts of a contactor are activated any time voltage is applied to the:

a. Coil
b. Power contacts
c. Auxiliary contacts
d. All of these

Answer: ________

A

control

a

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4
Q
  1. A __________________________ - pole contactor would be required to switch power to a three-phase load.
  2. Contactors may be used for switching motor loads when separate

__________________________________ protection is provided.

A

3

overload

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5
Q
  1. If the control circuit is connected directly to the same line wires as the load, then it must be rated for a lower voltage.___________________ (True or False)
  2. Pilot lights operating in conjunction with a contactor are normally controlled by auxiliary contacts.___________________ (True or False)
A

F

T

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6
Q

Identify the line side, load side, and parts of the contactor as shown in Figure 6-2.

A 
a plunger
b moveable contacts
c stationary contacts
d line side
e load side
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7
Q

Complete the wiring for the circuit drawn in Figure 6-3 connected so that the ON/OFF pilot switch switches the current to the three-phase heater load.

A

f

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8
Q
  1. With an _______________________ held contactor, the coil needs to be energized continuously all the time the main contacts are closed.
  2. A mechanically held contactor:
    a. Requires only a pulse of coil current to change state.
    b. Operates more efficiently than electrically held types.
    c. Is quieter than electrically held types.
    d. All of these

Answer: ________

A

electrically held

pulse of current

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9
Q

Complete the wiring for the lighting contactor circuit drawn in Figure 6-4 with the additional ON/OFF control station wired into the circuit.

A

f

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10
Q

The type of contact or operating mechanism shown in Figure 6-5 is the:

a. Clapper type
b. Bell-crank type
c. Seal-in type
d. Horizontal-action type

Answer: ________

Figure 6-5

A

horizonatal action

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11
Q
  1. A defective contactor coil will read zero or infinity, indicating a

_______________ or ______________ coil, respectively.

  1. Contactor coils are designed to operate:
    a. On AC only
    b. On DC only
    c. Over a range of 85 to 110 percent of rated voltage
    d. At rated voltage only
A

closed or open

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12
Q
  1. Operating contactor coils at either lower or higher than their rated voltage may result in a high level of contact bounce.

___________________ (True or False)

  1. AC and DC contactor coils with the same voltage ratings are normally interchangeable.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (True or False)
A

True

False

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13
Q
  1. The hold-in voltage rating of a contactor coil is normally:
    a. The same as the pickup voltage rating
    b. Less than the pickup voltage rating
    c. Greater than the pickup voltage rating
    d. The same as the dropout voltage rating
  2. Current flow through an AC coil is limited by both ______and _________________ .
A

b

resistance and reactance

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14
Q
  1. An AC contactor coil has a:
    a. High resistance (in Ohms)
    b. High inrush current
    c. A non-laminated steel core and armature
    d. All of these
  2. Whenever current to a contactor coil is turned off, a high-voltage spike is generated.___________________ (True or False)
A

B

True

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15
Q
  1. A broken or open shading coil will cause a contactor to become extremely noisy.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (True or False)
A

True

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16
Q

Identify the parts of the contactor assembly shown in Figure 6-7.

a. _________
b. _____________

Figure 6-7

A

shading coil

Core Laminations

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17
Q
  1. The core and armature of AC contactor assemblies are made of laminated steel to:
    a. Reduce chatter
    b. Reduce the size of the contactor
    c. Reduce eddy-current flow
    d. All of these
A

C

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18
Q
  1. A contactor fails to seat properly when energized. This may result in:
    a. Hum coming from the contactor
    b. Higher than normal current flow through the coil
    c. Overheating of the contactor coil
    d. All of these
  2. Contacts are silver-coated to reduce contact ____________________________ .
19
Q
  1. Auxiliary contacts are used to switch high-current load circuits.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (True or False)
  1. Silver contacts should never be filed.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (True or False)
  1. Arc current flow produces additional heat, which can damage
\_\_\_\_\_\_\_ surfaces.
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A

False

True

Contact

20
Q
  1. On opening under load, as the distance between contacts increases, the:
    a. Resistance of the arc remains the same
    b. Resistance of the arc increases
    c. Voltage required to sustain remains the same
    d. Voltage required to sustain the arc deceases
  2. An AC arc is self-extinguishing, as the arc will normally extinguish as theAC cycle passes through _______________________________ .
21
Q
  1. A motor would be classified as a(n):
    a. Resistive load
    b. Nonlinear load
    c. Inductive load
    d. Capacitive load
  2. Identify the parts of the contactor shown in Figure 6-8.
    a. ___________________
    b. _________________

Figure 6-8

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A

C

Arc Chute

Blowout coil

22
Q
  1. Blowouts are connected in series with the contacts.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (True or False)
  1. Worn contacts should always be replaced in pairs.

___________________ (True or False)

  1. A vacuum provides a better environment than free air for breaking the arc produced by opening contacts under load.

___________________ (True or False)

  1. A vacuum contactor does not use a coil to operate the contacts.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (True or False)
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A

tTrue

True

True

Fasle

23
Q

The contactor shown in Figure 6-9 would be classified as a

___________________________ type.

Figure 6-9

24
Q
  1. The NEMA size categorizes a contactor on the basis of

___________________, ___________, and

_____________ .

  1. Which of the following NEMA size contactors would have the greatest current carrying capacity?
    a. 0
    b. 3
    c. 6
    d. 9
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A

Current rating
Motor HP rating
Volt Rating

d

25
Name the contactor load utilization category for each of the following: a. Transformer: ________________ b. Incandescent lighting installation: ______________________ c. Electric furnace heater: ____________ d. Power factor correction bank: __________________________
Inductive Non-linear resistive Resitive Capacitive
26
4. NEMA contactors, as compared to IEC types, generally are physically downsized to provide higher ratings in a smaller package. ___________________ (True or False) 5. NEMA contactors are categorized by ___________________, while IEC types are categorized by ____________________________ categories.
T Standard sizes application
27
6. The two general classifications for NEMA contactor enclosures are ___________________________ location and _____________________ location. 7. Which of the following NEMA-type enclosures would be selected to ensure that an internal explosion would be confined to the inside of the enclosure? a. Type 1 b. Type 4X c. Type 9 d. Type 12
non hazard and hazard C
28
8. The IEC method for specifying the enclosures of electrical equipment is the same as that used by NEMA. ___________________ (True or False) 9. Solid-state switching refers to interruption of power by ____________ means. 10. A solid-state contactor: a. Has no contacts b. Is silent in operation c. Produces no arc d. All of these
F non- mechanical elctronc D
29
11. Identify the leads of the SCR solid-state switch shown in Figure 6-10. a. _______________ b. ____________ c. _____________ Figure 6-10
gate anode cathode
30
12. With reference to the SCR testing circuit shown in Figure 6-11, identify the SCR fault, if any, commonly associated with each of the following scenarios: a. Light turns on as soon as the power is applied. ____________ b. Light turns on when the on button is pressed and remains on when the button is released. ____________________________________________ c. Light fails to turn on when the ON button is pressed and power is applied. ____________________
SCR is shorted Normal operation SCR is faulted open
31
3. Zero-fired control of an SCR refers to triggering the SCR on at the maximum point of the sine wave so that no current is being switched under load. ___________________ (True or False)
T
32
2. In its most common form, a motor starter is a contactor with: a. An overload protection device b. An armature c. A circuit breaker d. A push button 3. The main purpose of an enclosure is to protect people from electric shock. ___________________ (True or False)
A t
33
Identify the major NEC requirements for the motor installation shown in Figure 6-13. a. _______________ b. ____________ c. ___________ d. __________ e. ________ Figure 6-13
``` DISCONNECT SHORT AND GROUND CONNECTION CONTACTOR ol PROTECTION DEVICE MOTOR DISCONNECT ```
34
6. A Class ___ overload relay will trip an overloaded motor offline within 20 seconds at six times full-load amperes. a. 20 b. 10 c. 40 d. 35 7. Once tripped, overload relays normally require a cooling-off period before they can be reset. ___________________ (True or False)
A t
35
8. Overload relays can be classified as being __________, _________, or _________. 9. External overload protection devices, which are mounted in the starter, attempt to simulate the heating and cooling of a motor by sensing the ________________________ flowing to it. 10. A thermal overload relay uses a heater element connected in parallel with the motor supply. ___________________ (True or False)
THERMAL MAGNETIC ELECTRONIC CURRENT f
36
A thermal overload relay protecting a three-phase motor requires __ heaters. a. 1 b. 2 c. 3 d. 4
c
37
Identify the parts of the thermal overload Figure 6-14. a. ______________________________________ b. ______________________________________ Figure 6-14
OL HEATER OL NC CONTACT
38
Identify the parts of the eutectic overload relay shown in Figure 6-15. a. b. ________
SOLDER POT HEAT PRODUCING ELEMENT
39
dentify the parts of the bimetallic overload relay shown in Figure 6-16. a. ______________________________________ b. ______________________________________ c. ______________________________________
HEATER ELEMENT BIMETALLIC STRIO TERMINAOLS
40
15. Selection tables for thermal overload relays normally list OL heaters according to motor ______________________________ . 16. Ambient temperatures will not normally affect the tripping time of a thermal overload relay. ___________________ (True or False) 17. Normally, in selecting OL heater sizes from a manufacturer's table, it is assumed that the motor: a. Has a minimum service factor of 1.1 b. Temperature rise is not over 104° F c. Will be protected up to 125 percent of the nameplate FLC rating d. All of these
FULL LOAD CURRENT f c
41
18. An electronic overload relay measures motor current directly through a current _____________________________ . 19. Electronic overload relays: a. Can be connected directly to the contactors b. Are easily adjustable to a wide range of full-load motor currents c. Reduce the amount of heat generated by the starter d. All of these
TRANSFORMER | D
42
20. Dual-element fuses, when properly sized, provide: a. Short-circuit protection b. Ground fault protection c. Overload protection d. All of these Answer: ________
D
43
Identify the elements of the dual-element fuse shown in Figure 6-18. a. __________________ b. ________________ Figure 6-18
short circuit element Overload Element
MOTORS MOTORS MOTORS B55a
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