Do You Know How to Read Basic Electrical Plans?

Estimated Completion Time
4 min
Do You Know How to Read Basic Electrical Plans?
Image: Busakorn Pongparnit / Moment / Getty Images

About This Quiz

Trying to build a house without blueprints is like trying to build a giant puzzle without looking at the picture as a guide. While a good contractor might be able to puzzle out things like walls and floors, it's impossible to install a complete electrical system without a well-prepared set of plans. 

Of course, these plans won't do you much good if you don't know how to read them. Designed by electrical engineers or pro electrical companies, these plans reveal everything from how the main source of power should enter the building, to the path wires should take throughout the structure, to the location of each and every light fixture, outlet, switch and piece of equipment. 

Electrical plans also reveal how electrical components will interact with other systems in the home. This includes where special power sources are needed, how air handling units and HVAC equipment will be powered, how fire alarms and smoke detectors will receive power and so much more required for a complete, safe and comfortable dwelling. 

Think you can interpret the various symbols and sayings on a standard electrical plan or blueprint? Prove your basic blueprint reading knowledge with this quiz!

Reflected ceiling plan
Wiki Commons by US Gov
Which drawing will give you locations for light fixtures?
Floor plans
Reflected ceiling plan
HVAC plan
Power riser diagrams
Correct Answer
Wrong Answer

The reflected ceiling plan is like a floor plan to show you what's happening on the ceiling. It's the perfect place to look when laying out light fixtures or other components that will be installed on the ceiling.

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CSI-spec-book
Tiffany / HSW
Which CSI spec book division covers electrical work?
12
18
26
49
Correct Answer
Wrong Answer

No set of electrical plans is complete without the accompanying set of spec books. For all the information you need as an electrician, check out Division 26, which is based on the widely-used Constructions Specification Institute system and covers all things electrical.

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Recessed fluorescent light
Wiki Commons by Dmitry G
If you see this figure on the plans, you should plan to install...
Recessed fluorescent light
Down light
Wall sconce
HVAC wiring
Correct Answer
Wrong Answer

This symbol is used on electrical plans to indicate a recessed fluorescent light fixture. If the fixture is meant to be surface-mounted rather than recessed into the ceiling, it is shown without the diagonal line passing from corner to corner.

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Panelboard-or-breaker-panel
Tiffany / HSW
This critical piece of electrical equipment is indicated by the symbol shown here.
Transformer
Thermostat
Switch
Panelboard
Correct Answer
Wrong Answer

A panelboard, or breaker panel, is the hub of a home's electrical service. It's where the power that has been fed into the building is divided among various circuits. This symbol indicates a surface-mounted panelboard when it is unfilled, or a flush-mounted panelboard when it is colored in.

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120-volts-single-receptacle
Tiffany / HSW
In the United States, this symbol is used to represent a single receptacle with this voltage.
30 volts
60 volts
120 volts
420 volts
Correct Answer
Wrong Answer

When you see this symbol, you should install a single 120-volt receptacle. If the symbol shows two lines passing through the circle, the intention is for the installer to use a duplex receptacle instead.

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Transformer-symbol
Tiffany / HSW
A solid box with a letter "T" inside on a set of electrical plans stands for this piece of equipment.
Thermostat
Terminal
Transit hub
Transformer
Correct Answer
Wrong Answer

Indicated on electrical plans via a box with the letter "T" inside, a transformer is an important piece of equipment for any home or building. This device increases or decreases the main power coming from the electrical grid, transforming it into a safe voltage for everyday use.

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Weatherproof-symbol
Tiffany / HSW
The letters WP in the notes on electrical plans usually mean....
Weatherproof
Wind-powered
Without purpose
Wisconsin proud
Correct Answer
Wrong Answer

The letters WP in the electrical notes indicate that the equipment in question should be rated as weatherproof. For instance, a weatherproof outlet comes with corrosion-resistant hangers, screws and contacts to hold up in outdoor use.

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GFCI-symbol
Tiffany / HSW
What does the G in GFCI stand for?
Good
Grey
Ground
Giant
Correct Answer
Wrong Answer

A ground fault circuit interrupter, or GFCI, is a special safety feature used on electrical outlets and other equipment. Required in almost all outdoor settings, and many indoor ones -- like bathrooms -- the GFCI feature stops the flow of power in a fraction of a second when a fault is detected.

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Circle-square-triangle-star
Tiffany / HSW
Which shape is used to indicate telecommunications fixtures on an electrical plan?
Circle
Triangle
Star
Square
Correct Answer
Wrong Answer

Telecommunications fixtures are indicated by tiny triangles on electrical plans. On larger projects, they may be included on a separate Telecommunications drawing. Blank triangles indicate data ports, while blackened triangles indicate phone ports.

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Circle-square-triangle-star
Tiffany / HSW
Which shape is used to indicate a junction box on an electrical drawing?
Circle
Square
Star
Triangle
Correct Answer
Wrong Answer

A junction box is a metal or plastic casing that is used to keep wire connections protected. These elements are indicated on electrical plans by a circle with the letter "J" inside.

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AFF-48-symbol
Tiffany / HSW
What do the letters AFF mean on an electrical plan?
Above finished floor
After filling fixtures
All fresh fixtures
Altered flux fixtures
Correct Answer
Wrong Answer

The letters AFF are commonly seen on building and electrical plans. When you see 48" AFF next to the symbol for a light switch, it means the switch should be installed 48 inches above finished floor.

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Plot plan
Wiki Commons by National Park Service
Which of these drawings is most likely to show wiring requirements outside of the home or building?
Reflected ceiling plan
Hardware schedule
Floor plan
Plot plan
Correct Answer
Wrong Answer

Plot plans show the electrician what is going to happen outside of the structure. This includes things like wiring locations and where equipment such as the transformer should be installed.

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Switch-letter-symbol
Tiffany / HSW
The letter "S" on an electrical drawing stands for...
Standard
Sideways
Switch
Solo
Correct Answer
Wrong Answer

The letter "S" on an electrical drawings simply stands for a single pole switch. A number after the S, such as S4, means that the installer should use a four-way switch.

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Wiring diagram
Machiner Restorer via YouTube
A number next to a wire helps you match the wire to the correct...
Breaker
Outlet
Switch
Transformer
Correct Answer
Wrong Answer

The number next to a wire on an electrical plan helps you match the wire to the correct breaker. These numbers, and the paths the wires will take, are shown on wiring diagrams.

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OS-symbol
Tiffany / HSW
The letters "OS" on an electrical plan stand for....
Otherwise shown
Over side
Other signs
Occupancy sensor
Correct Answer
Wrong Answer

The letters "OS" on an electrical plan stand for occupancy sensors. They may be listed in notes, or shown contained within a circle indicating where the sensor should be placed.

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Dimmer-switch-symbol
Tiffany / HSW
Which of these represents the typical symbol for a dimmer switch?
L-D
L-S
S-D
D-M
Correct Answer
Wrong Answer

The letter "S" on its own indicates a standard electrical switch. When the letter "D" is placed next to it, it indicates that the switch should be equipped with a dimmer function.

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Fluorescent-Fixture-tied-to-emergency-power-symbol
Tiffany / HSW
If the rectangular symbol indicating a fluorescent fixture is split diagonally, and one half is shaded, it means...
Fixture tied to emergency power
Fixture must be installed on wall
Fixture must have a shade on it
Fixture must have only one bulb
Correct Answer
Wrong Answer

A rectangular symbol split diagonally and shown on electrical drawings always indicates a fluorescent fixture. When half of the fixture is shaded and half is not, that means the fixture should be tied to emergency power. This means that the fixture will be powered by a backup supply if the main power goes out.

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Doorbell-pushbutton
Tiffany / HSW
What does a square symbol with a small black circle inside represent?
Thermostat
Doorbell pushbutton
Smoke alarm
Three-way switch
Correct Answer
Wrong Answer

A small square with a solid black circle inside indicates a doorbell pushbutton. Because this device relies on electricity, it is shown on the electrical plans so that it will be wired correctly.

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Recessed-fixture-symbol
Tiffany / HSW
A simple circle with a letter "R" inside on the reflected ceiling plan represents a...
Recessed fixture
Reversed fixture
Right-sized fixture
Fluorescent fixture.
Correct Answer
Wrong Answer

Circles shown on the reflected ceiling plan indicates round light fixtures called downlights. When there is an "R" inside the circle, that means the fixture should be recessed into the ceiling.

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Circuit-breaker-symbol
Tiffany / HSW
What does this common electrical symbol represent?
Copper wire
Exposed wiring
Wire turning up
Circuit breaker
Correct Answer
Wrong Answer

Circuit breakers are represented by various incarnations of this symbol. These breakers are designed to automatically stop the flow of current if a problem, such as a fault, is detected.

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Refrigrator-appliance-symbol
Tiffany / HSW
If you see this symbol next to the letters "Ref," plan your installation around a...
Reduced wire size
Refrigerator
Clothes washer
Dishwasher
Correct Answer
Wrong Answer

This symbol showing a circle with a triangle inside is used to represent a piece of equipment. Letters placed next to the symbol reveal what type of equipment will be used. Ref, for example, stands for refrigerator.

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Floor-outlet
Tiffany / HSW
This symbol on an electrical plan means an outlet should be installed here.
In the wall
In the ceiling
In the floor
Wherever it fits
Correct Answer
Wrong Answer

Electrical engineers and designers use symbols to not only indicate what type of equipment should be installed, but also where it should be placed. This symbol is always used for an outlet in the floor, which will usually be covered to keep dirt out and prevent the outlet from becoming a trip hazard.

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Branch-circuit-line
Tiffany / HSW
A continuous, uninterrupted line illustrating a branch circuit reveals that the circuit is...
For future use
Concealed in the floor
Concealed in the wall or ceiling
Exposed
Correct Answer
Wrong Answer

Branch circuits are used to divide and transfer power coming from the panel into various fixtures and equipment throughout a home or building. When the branch is shown as a continuous line on the drawings, that means it is meant to be concealed within the ceiling or wall.

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Branch-circuit-floor-symbol
Tiffany / HSW
Where should a branch circuit be installed if it's shown as a line segmented into a pattern of alternating short and long segments?
Inside ductwork
In the ceiling
In the floor
In the walls
Correct Answer
Wrong Answer

Branch circuits represented by a line broken into alternating long and short dashes should be concealed in the floor. These branch circuits are usually placed under access flooring or some form of panel so they can be accessed at a later time.

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Smoke-detector-symbol
Tiffany / HSW
What do the letters "SD" indicate on an electrical plan?
Smoke detector
Standard dimensions
Swinging door
Six dimmers
Correct Answer
Wrong Answer

Smoke detectors are often hard-wired in, which eliminates issues with dead batteries. This means they must be wired by the electrician so they will function properly. Most are indicated on drawings using either a circle or square with the letters SD inside.

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Thermostat-symbol
Tiffany / HSW
What should you install if you see the letter "T" in a circle on the electrical plans?
Transformer
Television
Timeclock
Thermostat
Correct Answer
Wrong Answer

The letter "T" enclosed in a circle is the standard symbol for a thermostat. To properly install this device, electricians must also reference wiring diagrams, which may be found on a separate details page.

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SP-special-purpose-outlet-symbol
Tiffany / HSW
The letters "SP" next to an outlet symbol stand for...
South paw
Special purpse
Standard dimension
Simple pair
Correct Answer
Wrong Answer

Many electrical outlets are designed for general use. Those with a special function may require extra amps or other modifications, and are indicated on the drawings by the letters "SP."

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TMGB-Symbol
Tiffany / HSW
Why would you want to use a TMGB?
It's a fire alarm.
It cuts energy costs.
It protects computer and data gear.
You probably wouldn't.
Correct Answer
Wrong Answer

A telecommunications main grounding busbar, or TMGB, is a critical device to help protect computer, phone and data equipment. This equipment is too sensitive to simply use standard grounding techniques, so a TMGB is added to protect the equipment in case of a fault or power surge.

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NEC-book-cover
Tiffany / HSW
When in doubt about electrical standards, refer to...
NEC
NDHA
EWO
MDOT
Correct Answer
Wrong Answer

The National Electric Code provides the minimum standards used in the electrical industry. Many electrical plans include NEC notes and references, which all electricians should be familiar with.

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UPS-symbol
Tiffany / HSW
The letters "UPS" on electrical plans stand for...
United Parcel Service
Uninterruptible power supply
United Power Standards
Until Panic Subsides
Correct Answer
Wrong Answer

The letters UPS stand for uninterruptible power supply. This is a battery=powered backup used to supply continuous power in case of an outage or other issue.,

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Branch-circuit-exposed-symbol
Tiffany / HSW
Where should you install a branch circuit that is indicated by a dashed line?
Leave it exposed
In the wall
In the ceiling
In the floor
Correct Answer
Wrong Answer

A branch circuit shown as a dashed line on the plans is meant to be left exposed. That could mean installing it in conduit, without placing it in the wall, ceiling or floor.

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Air handling unit
Wiki Commons by P199
What is an AHU?
Average height use
Artificial height unit
Air handling unit
All hail universe
Correct Answer
Wrong Answer

Air handling units are generally supplied and installed by the mechanical contractor, but the electrician also plays a role in finalizing the process. This includes adding specialty wiring and running the wiring to the device, though the scope may be further expanded on some projects.

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Explosion-proof-outlet-symbol
Tiffany / HSW
Which of these is most likely to require an explosion-proof outlet?
Chemical warehouse
Residential bathroom
Office space
Bedroom
Correct Answer
Wrong Answer

An outlet or other fixture shown with the letters "EP" beside it on the drawings should be rated as Explosion-Proof. This means it is designed so that a potential fault or spark inside the fixture won't ignite surrounding substances like vapors, gas or chemicals.

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Ground-symbol
Tiffany / HSW
When you see the letter "G" next to any symbol on an electrical plan, it means...
Gated
Grounded
Generous
Giant
Correct Answer
Wrong Answer

Electrical grounding is critical for safety, and is represented on electrical plans by the letter "G" -- "UNG" stands for ungrounded. Grounding is accomplished by techniques like using a second neutral wire when pulling wires, or by using that third prong you see on things like an extension cord.

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Blank-outlet-symbol
Tiffany / HSW
What does it mean if an outlet is marked with a letter "B" on the plans?
Brand-new
Ballasted
Blank
Borrowed
Correct Answer
Wrong Answer

An outlet annotated with a letter "B" on the plans is meant to be blank. This means it should be wired for future use, but won't be used immediately and typically requires only a blank cover.

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Standard-conduit
Tiffany / HSW
What is the most common number of wires used in a standard conduit?
2
4
8
12
Correct Answer
Wrong Answer

A standard conduit contains two wires -- one that is live and one neutral wire for grounding. Circuits shown on the drawings with a number indicate that the installer should use that quantity of wires.

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Turn-wire-towards-ceiling
Tiffany / HSW
What should you do with a wire if you see this symbol?
Splice it
Replace it with copper
Turn it up toward the ceiling
Terminate it
Correct Answer
Wrong Answer

This symbol means that a wire should be turned up. The same symbol in which the circle is filled in means that the wire is meant to be turned down toward the ground.

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Amp-reads-current
Tiffany / HSW
What do amps measure?
Current
Voltage
Speed
Sound
Correct Answer
Wrong Answer

Amps measure current. A standard residential circuit measures 15 to 20 amps, which means it can accommodate 1800 to 2400 watts before it flips.

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DS-ES-M-NT-symbols
Tiffany / HSW
Which of these is not a symbol the electrician should be aware of when it comes to door hardware?
Box marked DS
Box marked ES
Box marked M
Box marked NT
Correct Answer
Wrong Answer

As door hardware becomes more advanced, the installation of this hardware requires a joint effort between the hardware installer and an electrician. Look out for hardware symbols like DS, ES and M, which stand for door switch, electric strike and mag lock.

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Security-camera-symbol
Tiffany / HSW
What does this symbol indicate on an electrical drawing?
TV speaker
Security camera
Standard outlet
Light switch
Correct Answer
Wrong Answer

This symbol represents a security camera. The number of cameras shown on the symbol generally equates to the number and pattern that should be installed.

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