Electrical Final Flashcards by D K

What is AWG?

American Wire Gauge.

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What does NEC stand for?

National Electric Code

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What ohmic value shows continuity?

0.1 Ohms or above

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What is a load center?

The central location which distributes power.

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What should you do before making any electrical repair?

Check for source voltage

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What does NEMA stand for?

National Electrical Manufacturers Association

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What does IEC stand for?

International Electrotechnical Commission

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How are IEC relays sized?

Numbers

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What are the rings of magnetism called around the wire?

Lines of flux.

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Depending on design, relays normally do not control power-consuming devices directly, except for small loads which draw less than ___ A.

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The two major types of relays are the ___ relay and the solid-state relay.

Electromechanical

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A(n) ___ relay is a switching device that has no contacts and switches entirely by electronic means.

Solid State

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___ relays are designed for commercial and industrial applications where economy and fast replacement are high priorities.

General Purpose

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A ___ is the number of completely isolated circuits that a relay can switch.

Pole

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A double-throw contact can control ___ circuits.

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___ relays are the backbone of electromechanical control circuitry and are expected to have a long life and a minimal amount of problems.

Machine Control

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A(n) ___ relay is a fast-operating, single-pole, single-throw switch with NO contacts hermetically sealed in a glass envelope.

Reed

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Because they are sealed, ___ relays are unaffected by dust, humidity, and fumes and have a long life expectancy.

Reed

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___ contacts have an open contact resistance of several million ohms.

Reed

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A ___ magnet is the most common actuator for a reed relay.

Permanent

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___ motion is not a method of proximity motion operation.

Rotating

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A ___ switch contains a float, a moving magnet, and a magnetically operated reed switch to detect the level of a liquid.

Magnetic Level

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Typical ___ life ratings for electromechanical relays are 1,000,000 to 10,000,000 operations.

Mechanical

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A contact protection circuit may contain a(n) ___ or a metal-oxide varistor (MOV).

Diode

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___ has the highest electrical conductivity of all metals.

Fine Silver

Sulfidation increases the ___ of the contacts.

Resistance

___ contacts are used in high-voltage applications because they have high melting temperatures and are less affected by arcing.

Tungsten

Overvoltage or undervoltage conditions of more than ___% in relays should be corrected.

0.1

Are relays usually used to control higher current loads, such as a 20A electric motor?

No, 15A or lower.

Does the load controlled by the contacts need to be the same voltage as the coil?

Can 1 relay control several different contacts?

Yes

Can a relay with multiple contacts use the different contacts to control different loads, each with different voltages?

Yes

What does DPST-DB stand for?

Double Pole, Single Throw, Double Break

Which relay type has convertible contacts which can be placed in NO or NC condition?

Machine Control Relay

Are reed relays usually used for loads between .1A to 10A?

Why are gold-flashed silver contacts used in automobile air bag activation control systems?

Resists sulfidation

Should relay contacts be filed when showing signs of wear?

In a 120 V circuit, is it acceptable when 2 V are measured across a closed contact operating a load?

In a 120 V circuit, is it acceptable when the full 120 V are measured across an open relay contact?

Yes

What is the definition of a relay?

A device that controls 1 electrical circuit by opening and closing contacts in another circuit.

A small voltage applied to a relay results in ___

A larger voltage being switched.

It's the current rating for DC higher or lower than AC?

Lower

What is a pole?

Number of completely isolated circuits that a relay can switch.

What is a throw?

The number of closed contact positions per pole.

What is a break?

The number of separate places on a contact that open or close in an electrical circuit.

__ ___ ___ are designed where economy and fast replacements are high priority.

General Purpose Relays

Does the iron core of electromagnet increase or decrease the magnetic lines of force?

Increase

In an electromagnet, what determines the strength of the magnetic field?

Current

What is the left hand rule used to determine when the direction of current flow is known?

Polarity

What is the movable part of a solenoid?

Armature

Why are solenoid armatures laminated?

Reduce Eddy Current (which creates heat)

Why is a shading coil added to the armature of a solenoid?

Hold onto the armature when magnetic flow drops.

What is the initial current draw of a solenoid called?

Inrush Current

What is the operating current of a solenoid called?

Sealed Current

If the voltage applied to a solenoid is higher than the rating of the solenoid, will the current draw increase, or decrease?

Increase

What is the number of times a solenoid can operate in a given time period called?

Duty Cycle

What type of valve is used to direct the flow of fluid?

DCV (Directional Control Valve)

What is the number of locations within a valve in which a spool is placed to direct fluid through the valve called?

Positions

What is a flow path through a valve?

Ways

What does an electrical control valve use to change position of a valve spool?

Actuator

What is the acceptable voltage range that should be applied to a solenoid?

±10% of the rated value

What device is used to reduce transient produced by solenoids?

Snubber Circuits

What is the acceptable resistance range that should be measured when testing a solenoid?

±15%

In a truth table, X represents what contact condition?

Closed Contact

In a truth table, O represents what contact condition?

Open Contact

If the moving part of a limit switch is drawn below the contacts in the symbol, is the switch NO/NO held closed or NC/NC held open?

NO/NO held closed

If the moving part of a limit switch is drawn above the contacts in the symbol, is the switch NO/NO held closed or NC/NC held open?

NC/NC Held Open

If a pressure switch is used to maintain a set pressure, are NO or NC contacts used to control the compressor motor starter?

If a temperature switch is used in a heating system to maintain a set temperature, are NO or NC contacts used to control the heating contactor?

If a temperature switch is used in a cooling system to maintain a set temperature, are NO or NC contacts used to control the cooling contactor?

If a flow switch is used to sound an alarm when there is no flow, are NO or NC contacts used to control the alarm?

If a flow switch is used to detect flow in an automatic sprinkler system that had detected a fire and opened the sprinklers to flow, are NO or NC contacts used to control the alarm?

If a level switch is used in a charging system, are NO or NC contacts used to control the pump motor starter?

If a level switch is used in a disharging system, are NO or NC contacts used to control the pump motor starter?

Is a diode used to help protect electrical contacts in an AC or DC load switching circuit?

If voltage is measure on the incoming side of a switch, but not on the outgoing side, what is the state of the switch?

It is open

If voltage is measured on both sides of a switch, what state is the switch in?

Closed

What does CEMF stand for?

Counter Electro-Motive Force

Can 1 push-button operate both NO and NC contacts?

Yes

What are the two windings of a transformer called?

Primary and Secondary

If a transformer has a turns ratio of 1:4, what is the voltage ratio?

4:1

If a transformer has a turns ratio of 1:4, what is the current ratio?

1:4

If a transformer has a turns ratio of 1:4, what is the power ratio?

1:1

Why are transformer iron cores laminated?

Minimize Eddy Current Losses, which produce heat

What type of electrical service is most common for residential dwellings?

120V/240V single phase

Why do control transformers usually have two primary coils?

So you can use different voltages (Tyically 240V or 480V)

What do "X" markings on a transformer represent?

Lower Voltage

What do "H" markings on a transformer represent?

High Voltage

When connecting the primary of a control transformer to high voltage, are the coils connected in series or parallel?

Series

When connecting the primary of a control transformer to low voltage, are the coils connected in series or parallel?

Parallel

Is a transformer's VA rating based on the primary ot secondary of a the transformer?

Secondary

What information is needed to size a transformer?

•Input Voltage Available •Output Voltage Desired •Output Current Required

Can you use a transformer for DC voltage?

What stays the same in a series circuit?

Current

What stays the same in a parallel circuit?

Voltage

What adds in a series circuit?

Resistance and Voltage

What adds in a parallel circuit?

Current

What is the formula for resistance in a parallel circuit?

(R1xR2) ________ (R1+R2) OR 1/R1+1/R2...

What is needed to keep a motor running after pressing a momentary push button?

Normally Open Aux Tips in parallel with the button. AKA Normally Open Seal in Tips

What are the 5 components that create a circuit?

1. Source Voltage 2. Wire 3. Switching Device 4. Load 5. OCPD (Fuse/Breaker)

What is a solenoid?

Electrical device which converts electrical energy to linear mechanical motion.

What do bold lines in a circuit’s diagram identify?

Power Circuit

What do light lines in a circuit’s diagram identify?

Control Circuit

What is the symbol for an LED?

Diode with 2 arrows pointing out. ▶️|↗️↗️

What is ghost voltage?

Voltage created from magnetic energy generated by conductors, lights, etc. Can be measured in the air.

What is the minimum rating for DMMs in the mill?

Cat 3

What is it called when a 3 phase connection/motor loses 1 phase?

Single Phasing

How is a 3 phase motor wired?

1-L1 2-L2 3-L3 4-7 5-8 6-9

What does ESD stand for?

Electro Static Discharge

Which diagram shows the relationship between components but not their locations?

Ladder Diagram

What does OCPD stand for?

Over Current Protection Device

What protects a running motor?

Thermal Overloads

What protects a motor when starting?

Fuses

What shows length, width, and height in 1 view?

Pictorial View

What is a manual circuit?

A circuit which requires an actual person to actuate/energize it

How do you check a fuse with power off?

Ring it out for continuity

How do you check a fuse with power on?

Meter fuse for voltage. (Should show 0V)

What should you read if you meter 480VAC phase to ground?

277VAC

What's the formula for Voltage(E)?

E=IxR

What's the formula for Resistance(R)?

R=E/I

What's the formula for Current(I)?

I=E/R

What is the formula letter for SPST-NO?

What is the formula number for SPST-NC?

What is the form letter for SPDT?

C (Most common)

Electrical Final Flashcards

(124 cards)