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Electrical > Book #5 > Flashcards

Book #5 Flashcards

1
Q

Which type of three-phase motor has a high starting torque?

A

Wound-rotor motor

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2
Q

An overhead hoist is operating with a wound rotor motor. The three-phase motor cannot lift the load and now some of the resistors are glowing red, what is the probable cause?

A

one resistor bank is open

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3
Q

When shall only pylons and protective tape be acceptable for protection of hazards?

A

Open trench

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4
Q

How is the thermostat connected in a force flow electric furnaces control circuit?

A

In series with the coil

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5
Q

What is the preferred voltage and current ratings for the secondary of instrument transformers

A

120v, 5a

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6
Q

When batteries are used as a source of supply, the batteries shall be kept:

A

Fully charged at all times

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7
Q

What type of contact is the fan limit control in a forced air furnace

A

Normally open, closes on temperature rise

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8
Q

What type of dc motor is effective for constant speed characteristics

A

Shunt Motor

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9
Q

What type of control is required to be part of a motors installation, when automatic restarting of the motor would not create a hazard

A

Low-voltage release

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10
Q

The load requirement of a dc motor is for an extremely high starting torque, if speed regulation is not important, what type of motor will satisfy the installation?

A

Series motor

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11
Q

Why are some components of a PLC circuit hard-wired instead of going through the controller?

A

Safety

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12
Q

If the high limit switch in a gas furnace control is interchanged with the fan control, what would happen?

A

Fan would run constantly

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13
Q

What type of gas is released in a battery storage room?

A

Hydrogen

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14
Q

A wound rotor motor fails to start, but will run when the three slip rings are short circuit. What is the likely condition indicated by this type of fault and troubleshooting?

A

Open lead in the rheostat

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15
Q

What characteristics will a shunt field winding have?

A

High resistance, few turns

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16
Q

The centrifugal switch of a resistance-start induction-run split-phase motor is stuck closed. what will likely happen to the motor?

A

Start windings will burn out

17
Q

When using a GFCI circuit, what should be done to prevent nuisance trips?

A

Separate the bonding and the identified in the circuit

18
Q

What would be the reason that a synchronous motor has not yet synched up?

A

Has not been excited with DC

19
Q

An ohmmeter reads infinity across the leads of a capacitor, what is the status of the capacitor?

A

Good

20
Q

What is the result of a cadweld connection when damp or wet mould is used on a weld in a ground electrode installation

A

Weld would be porous

21
Q

A prony brake is used to measure:

A

Torque

22
Q

The DC generator terminals marked F1 and F2 are:

A

Shunt field leads

23
Q

In order to increase the DC generator voltage:

A

The field current should be increased

24
Q

The function of the brushes in a DC generator is to:

A

carry the current to the external circuit

25
Q

The DC compound generator is a combination of:

A

a series and shunt generator

26
Q

Armature reaction is main field distortion caused by:

A

Armature current

27
Q

The DC generator will normally use brushes that are constructed from which of the following material?

A

Carbon

28
Q

The main purpose of commutating poles or inter-poles in a DC motor is to:

A

Counteract armature reaction and thus reduce sparking at the brushes

29
Q

An example of a non-automatic pilot device would be a:

A

Momentary push button

30
Q

A service call comes in that a gas-fired boiler shows a flame out on the annunciator panel. a new high-voltage igniter is installed and the problem is fixed. What was the original problem?

A

Broken porcelain on the igniter

31
Q

Gloves used for protection when working with high voltages should be tested:

A

before every use

32
Q

What period of time is a circuit breaker protecting a fire pump to carry locked rotor current of the fire pump, according to NFPA No. 20

A

8 to 20 seconds

Electrical (13 decks)

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