Second Year Electrical Lab

The labelling of the coil terminals of different relays may vary depending upon rating agency and manufacturer

True

A contactor coil and its moveable contacts are physically linked together

False

In a relay, a set of normally open contacts are in the open position when the relay coil is

De-energized

What is the main difference between a relay and a contactor?

The current rating of their contacts

Which type of relay has an open-type exposed contacts?

Power relay

What is the function of the mechanical interlock block in a reversing contactor?

To prevent both armatures from closing at the same time

Which form identifies a single-pull, single throw , normally closed bridge contact?

Form Y

What is the moveable portion of a relay called?

Armature

How are eddy currents reduced in a contactor?

By laminating the core material

What would be the effect on a contactor if the contact springs were too loose?

They would not maintain proper pressure on the contacts after they come together

What is the approximate seal-in voltage of a 120 V rated relay coil?

102 V

What is the function of shading coils in a contactor?

They reduce contact chatter while the coil is energized

What is the main disadvantage of using copper contacts in a contactor?

They are prone to pitting and oxidation

Which type of timer is best suited for a bathroom fan?

Spring wound interval timer

Which timing relay function always requires a start signal?

One-shot

Which statement best describes the normally open (NO) contacts of a TDOE timing relay at the instant the relay coil is energized?

Open, timing to close

An interval timing relay is set for 5 seconds. If the relay coil for this timer has been energized for 12 seconds, what must happen for the contacts to change state again?

The relay coil must be de-energized and then re-energized

What is the difference between a smart relay and a timing delay?

Smart relays can be programmed to provide many timing functions

In a smart relay, which timing function would be used to delay an action for a set period of time after an input signal is received?

On-delay timing

Automatically operated pilot devices detect a change and convert this change to the opening or closing of a set of contacts

True

When drawing a pressure switch in a diagram, the symbol is drawn as though there is _____ pressure in the system

No

A short-circuit path has a ____ impedance than a normal circuit path

Lower

What is the function of the holding contacts in a basic stop/start control circuit?

To keep the motor running when the start button is released

If an additional stop button is to be connected to an existing stop/start control circuit, how would it be connected?

In series with the other stop button

What is a start push button an example of?

Manually operated, momentary control device

Which of the following is a non-contact pilot device?

Proximity switch

What will an inverse-time circuit breaker protect a general-purpose circuit from?

Overloads and short circuits

What is meant by the term “trip-free” when applied to a circuit breaker?

The breaker must trip, even if locked or held in the closed position

Which of the following is not a factor in determining the maximum available short-circuit current in a system?

Ampacity of the supply conductors

A motor is expected to 

Draw a high current at the start up

What is the fault current caused by

A low impedance path to ground

Which type of diagram provides information about the system and the relative location of each component without going into detail

Block

Electrical drawings are never a combination of drawings

False

Which is not a type of electrical wiring

Elementary

Which type of diagram shows the connection of devices with respect to physical location?

Wiring

What other name is a schematic diagram sometimes referred to as?

Ladder

Which is a feature of a schematic diagram?

Shows the sequence of operation of an electrical system

Which type of diagram shows all the wires carried between electrical components?

Wiring

Contacts are always drawn as if the coil is 

De-energized

Interchanging push buttons that are connected in series electrically alters a circuit

False

Which type of electrical diagram shows the detailed wiring of electrical equipment

Wiring

Which is the most common type of interconnection diagram?

Termination schedule

Which type of drawing shows the sequence of operation in its simplest form, which can aid in troubleshooting the circuit?

Schematic

A schematic diagram is shown in what condition?

With the power off and the mechanical system empty

How are the contacts on a schematic labelled?

To identify which relay coil or contactor controls them

What advantage does a schematic diagram have over a wiring diagram?

It is easier to understand the sequence of operation of the circuit

The NC contacts of a thermal overload relay are connected in the

Control circuit

Which type of device is a bimetallic overload relay?

Thermal

Which of the following examples best describes an overload condition?

A motor with excess mechanical load

A motor has an ambient temperature rating of 40 degrees Celcius and a temperature rise rating of 60 degrees Celcius. What is the expected internal temperature of this motor at full load conditions?

100 degrees Celcius

Which circuit are the overload heaters connected in?

The power circuit

What is another name for manual motor circuit switches?

Manual motor starters

What can a motor with a high service factor do?

Withstand a longer duration of overload

Which of the following does not affect the selection of motor branch circuit overcurrent devices?

Motor service factor

What is the maximum overload rating for a 25 A, 460 V, three-phase motor with a service factor of 1.1?

28.75 A

An ohmmeter measures 150 ohms between Terminal 3 and L2 of a NEMA starter when the armature is pushed in by hand. What does this reading indicate?

A normal condition

Which of the following is not a section of a basic stop/start control circuit?

The power circuit

Two pressure switches, one for high-pressure and one for low-pressure, control a compressor motor to maintain high pressure in a vessel. Which of the following statements best describes the high-pressure switch?

Normally-closed, used to stop the compressor motor

A pressure switch is required to prevent a three-phase motor from being started, but it will not stop the motor if it is already running. In which circuit would the contacts of the pressure switch be located?

The start circuit

A limit switch is required to prevent a three phase motor from being started, and it will also stop the motor if it is already running. In which circuit would the contacts of the limit switch be located?

The stop circuit

The pilot light is required to indicate when the control circuit of a NEMA motor starter is energized. To which terminals should the pilot light be connected?

Terminals L1 and L2

Which statement best describes low-voltage release?

The motor may or may not restart automatically upon restoration of power

When would a 3-wire control circuit not provide low-voltage protection?

When the control devices are automatic pilot devices

How is the direction of rotation of a three-phase motor reversed?

By interchanging any two lines to the motor

How many power contacts does a reversing motor starter requre?

6

Which interlock in a reversing motor starter prevents both armatures from being able to pull in at the same time?

Mechanical

A pilot light to indicate that a motor is running in the reverse direction would be connected across Terminals ____ and L2 in a NEMA reversing motor starter

7

Which numbers are used to identify the reverse holding contacts in an IEC reversing motor starter?

13 and 14

Where should a pilot device that will affect both the starting and running of a motor in only the reverse direction be connected?

Reverse stop circuit

A pilot light allows a motor to be started but stops the motor from running in the forward direction. Where should this device be connected?

Forward holding circuit

Conduction is the way heat is transferred by

Solids

Automatic control systems can monitor and respond to which variable conditions in the environment?

All of the above

Which bimetal temperature sensing device is best used in high current applications?

Disk

Which thermostat contact is the most used?

Mercury contacts

The measurement of 1 Btu is the amount of energy to raise what?

1 pound of water 1 degree Farenheit

The transfer of heat energy can be achieved through three methods: radiation, convection, and

Conduction

What are the four factors of human comfort?

Humidity, air movement, radiation, temperature

A bimetal strip in a thermostat consists of two different metals, one of which has a high rate of thermal ______ compared to the other

Expansion

What is the best type of temperature-sensing devices for monitoring the temperature in a pipe of tank?

Liquid bulb

What is a solid state temperature-sensing device that has a negative temperature coefficient?

Thermistor

In a cooling thermostat, the anticipator is connected in _____ with the contacts

Parallel

Where is the best location to install a thermostat?

In a hallway

What class of power does a step-down transformer used in a furnace provide?

Class 2

The combustion air blower forces air directly into the

Plenum

The primary high limit switch is a normally closed device that opens if excessive temperature is sensed

In the heat exchanger compartment

What voltage does an intermittent pilot ignition system require?

A very high stepped up voltage

Which furnace terminal does the interlocking relay connect to?

R and G

Which component of an electric heating system is responsible for controlling the temperature of the space?

Thermostat

What is the purpose of the step open gas valve opening in two stages?

To reduce the ignition explosion in the heat exchanger

Where is a 120 V heating system most commonly used?

Commercial garages

What does the thermocouple in a gas-fired furnace provide power for?

Power unit

What is the open circuit voltage for the thermocouple?

26-32 mV dc

Which device is operated through manipulation of gas pressure?

Diaphragm gas valve

How should the summer switch be wired?

Parallel to the fan controller

What should the fan off setting be set between on a basic forced air system?

32-38 degrees Celcius

What is a furnace with an efficiency rating of 82% classified as?

Mid-efficient

What is the purpose of the combustion air blower?

To move air through the heat exchanger

Where would the sensing portion of a secondary high limit device be placed?

Blower compartment

What is the purpose of an HRV?

To recover the heat from the exhaust fan

What condition is the refrigerant in when leaving the compressor in the discharge line?

Hot, high pressure, and a vapour