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2nd Period Electrical Lab > Pilot and Overcurrent Devices 030204c > Flashcards

Pilot and Overcurrent Devices 030204c Flashcards

1
Q

What are holding contacts also referred to as?

Pilot and Overcurrent Devices ILM

A

Seal-in contacts.
Sealing contacts.
Maintaining contacts.

Pilot and Overcurrent Devices ILM
Page 6

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2
Q

What is a pilot device?

Pilot and Overcurrent Devices ILM

A

Signals a change in condition by opening or closing a set of contacts.
Can be either a maintained or momentary type switch.

Pilot and Overcurrent Devices ILM
Page 11

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3
Q

What are automatically operated pilot devices?

Pilot and Overcurrent Devices ILM

A

Change states without requiring a person to operate them.

Pilot and Overcurrent Devices ILM
Page 14

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4
Q

Automatic pilot devices can be used to detect changes in:

Pilot and Overcurrent Devices ILM

A

Temperature.
Pressure.
Liquid levels.
Thickness of materials.
Light.
Rotation.
Specific gravity.
Vibration.
Linear movement.
Flow of liquid.

Pilot and Overcurrent Devices ILM
Page 14

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5
Q

What are some examples of temperature sensors?

Pilot and Overcurrent Devices ILM

A

Thermocouples.
Resistance temperature detectors (RTDs).
Thermistors.
Infrared sensors.
Bimetallic devices.
Silicon diodes.

Pilot and Overcurrent Devices ILM
Page 15

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6
Q

What is a thermocouple?

Pilot and Overcurrent Devices ILM

A

A device that measures temperature by producing a change in voltage.
As temp goes up voltage goes up.
Flame proving device.

Pilot and Overcurrent Devices ILM
Page 16

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7
Q

How do infrared sensors function?

Pilot and Overcurrent Devices ILM

A

Do not need to touch the surface being measured.
Measures the temperature of the surface by its thermal radiation.

Pilot and Overcurrent Devices ILM
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8
Q

What type of sensor can measure the temperature of moving objects?

Pilot and Overcurrent Devices ILM

A

Infrared Sensors.

Pilot and Overcurrent Devices ILM
Page 16

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9
Q

How do Bimetallic devices work?

Pilot and Overcurrent Devices ILM

A

Two metals are bonded together and mechanically linked to a set of contacts.
When heated one side of the strip will expand more causing the strip to bend and activate the contacts.

Pilot and Overcurrent Devices ILM
Page 16

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10
Q

What type of sensors can be used in a wide range of temperatures including cryogenic temperatures of -150°C?

Pilot and Overcurrent Devices ILM

A

Silicon Diode sensors.

Pilot and Overcurrent Devices ILM
Page 16

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11
Q

What is the difference between a limit switch and a proximity switch?

Pilot and Overcurrent Devices ILM

A

Limit switches require the actuator, lever, cam, or rod to contact the object or material being sensed.
Proximity switches can detect the object or material without contacting it.

Pilot and Overcurrent Devices ILM
Page 17

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12
Q

What are some types of proximity switches?

Pilot and Overcurrent Devices ILM

A

Magnetic.
Inductive.
Capacitive.
Photoelectric.

Pilot and Overcurrent Devices ILM
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13
Q

How does a magnetic proximity switch work?

Pilot and Overcurrent Devices ILM

A

Detects the presence of an external magnetic field.

Example: Security system sensors or hall effect sensors.

Pilot and Overcurrent Devices ILM
Page 17

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14
Q

How do Inductive proximity switches work?

Pilot and Overcurrent Devices ILM

A

Operate by creating a magnetic field and then sensing when a conductive metal object enters that field.

Example: Sensors under road construction materials at traffic lights.

Pilot and Overcurrent Devices ILM
Page 17

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15
Q

How do capacitive proximity switches work?

Pilot and Overcurrent Devices ILM

A

Create an electrostatic field and then sense when an object enters that field.

Pilot and Overcurrent Devices ILM
Page 18

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16
Q

How do photoelectric proximity switches work?

Pilot and Overcurrent Devices ILM

A

Sense light reflected off an object or sense when an object interrupts a light beam.

Example: Garage door sensors.

Pilot and Overcurrent Devices ILM
Page 18

17
Q

What are two types of float switches?

Pilot and Overcurrent Devices ILM

A

Lever actuated by a mechanical float and rod.

Tethered bulb.

Pilot and Overcurrent Devices ILM
Page 18

18
Q

When does an overcurrent condition occur?

Pilot and Overcurrent Devices ILM

A

Occurs when the current in the circuit exceeds the normal continuous operating amount.

Pilot and Overcurrent Devices ILM
Page 21

19
Q

What is an overload condition?

Pilot and Overcurrent Devices ILM

A

When current is a moderate percentage above the normal current for the circuit for long enough to cause damage.

Pilot and Overcurrent Devices ILM
Page 22

20
Q

What ratings do all overcurrent devices, fuses and circuit breakers need to have?

Pilot and Overcurrent Devices ILM

A

Voltage rating.
Continuous current rating.
Interrupting rating.

Pilot and Overcurrent Devices ILM
Page 22

21
Q

What does the continuous current rating indicate?

Pilot and Overcurrent Devices ILM

A

Indicates the amount of current the device can carry without exceeding a specified temperature rise.

Pilot and Overcurrent Devices ILM
Page 23

22
Q

What does the interrupting rating indicate?

Pilot and Overcurrent Devices ILM

A

Indicates the maximum amount of current the device can safely interrupt when it opens during a short-circuit condition.

Pilot and Overcurrent Devices ILM
Page 23

23
Q

What are the two basic types of overcurrent devices?

Pilot and Overcurrent Devices ILM

A

Fuses.
Circuit breakers.

Pilot and Overcurrent Devices ILM
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24
Q

What are the two basic types of cartridge and plug fuses?

Pilot and Overcurrent Devices ILM

A

Non-time delay fuses. (Single-element)
Time-delay. (Dual-element)

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Page 25

25
Q

What type of fuse is also known as a single-element fuse?

Pilot and Overcurrent Devices ILM

A

Non-time delay fuses.

Pilot and Overcurrent Devices ILM
Page 25

26
Q

What type of fuses are also known as dual-element fuses?

Pilot and Overcurrent Devices ILM

A

Time-delay fuses.

Pilot and Overcurrent Devices ILM
Page 26

27
Q

What are the two parts of a time-delay/dual-element fuses?

Pilot and Overcurrent Devices ILM

A

A thermal cut-out.
Fuse element or link.

Pilot and Overcurrent Devices ILM
Page 26

28
Q

What are the two types of circuit breakers?

Pilot and Overcurrent Devices ILM

A

Instantaneous-trip.
Inverse-time. (Thermal-magnetic)

Pilot and Overcurrent Devices ILM
Page 28

29
Q

Which type of circuit breaker has both a bimetallic tripping element as well as an electromagnetic element?

Pilot and Overcurrent Devices ILM

A

Inverse-time

Protect against overload and short-circuit conditions.

Pilot and Overcurrent Devices ILM
Page 29

30
Q

What type of condition do instantaneous-trip circuit breakers only respond to?

Pilot and Overcurrent Devices ILM

A

Short-circuit conditions.

Pilot and Overcurrent Devices ILM
Page 28

31
Q

What is a trip-free mechanism on a circuit breaker?

Pilot and Overcurrent Devices ILM

A

Allows circuit breaks to still trip and de-energize even if they are locked in the on position.

Pilot and Overcurrent Devices ILM
Page 32

32
Q

What factors affect the maximum available fault current?

Pilot and Overcurrent Devices ILM

A

kVA rating of the transformer.
Voltage rating of the transformer secondary supplying the circuit.
Percent impedance voltage of the transformer.

Pilot and Overcurrent Devices ILM
Page 36

33
Q

How does the distance of a short circuit from the source impact the fault current?

Pilot and Overcurrent Devices ILM

A

The closer the short circuit occurs to the source the lower the impedance and greater the fault current.

Pilot and Overcurrent Devices ILM
Page 36

2nd Period Electrical Lab (13 decks)

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