Book #5 Flashcards
Which type of three-phase motor has a high starting torque?
Wound-rotor motor
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?
one resistor bank is open
When shall only pylons and protective tape be acceptable for protection of hazards?
Open trench
How is the thermostat connected in a force flow electric furnaces control circuit?
In series with the coil
What is the preferred voltage and current ratings for the secondary of instrument transformers
120v, 5a
When batteries are used as a source of supply, the batteries shall be kept:
Fully charged at all times
What type of contact is the fan limit control in a forced air furnace
Normally open, closes on temperature rise
What type of dc motor is effective for constant speed characteristics
Shunt Motor
What type of control is required to be part of a motors installation, when automatic restarting of the motor would not create a hazard
Low-voltage release
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?
Series motor
Why are some components of a PLC circuit hard-wired instead of going through the controller?
Safety
If the high limit switch in a gas furnace control is interchanged with the fan control, what would happen?
Fan would run constantly
What type of gas is released in a battery storage room?
Hydrogen
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?
Open lead in the rheostat
What characteristics will a shunt field winding have?
High resistance, few turns
The centrifugal switch of a resistance-start induction-run split-phase motor is stuck closed. what will likely happen to the motor?
Start windings will burn out
When using a GFCI circuit, what should be done to prevent nuisance trips?
Separate the bonding and the identified in the circuit
What would be the reason that a synchronous motor has not yet synched up?
Has not been excited with DC
An ohmmeter reads infinity across the leads of a capacitor, what is the status of the capacitor?
Good
What is the result of a cadweld connection when damp or wet mould is used on a weld in a ground electrode installation
Weld would be porous
A prony brake is used to measure:
Torque
The DC generator terminals marked F1 and F2 are:
Shunt field leads
In order to increase the DC generator voltage:
The field current should be increased
The function of the brushes in a DC generator is to:
carry the current to the external circuit
The DC compound generator is a combination of:
a series and shunt generator
Armature reaction is main field distortion caused by:
Armature current
The DC generator will normally use brushes that are constructed from which of the following material?
Carbon
The main purpose of commutating poles or inter-poles in a DC motor is to:
Counteract armature reaction and thus reduce sparking at the brushes
An example of a non-automatic pilot device would be a:
Momentary push button
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?
Broken porcelain on the igniter
Gloves used for protection when working with high voltages should be tested:
before every use
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
8 to 20 seconds
