• SkillCat Team

Electrical Wiring Symbols

Updated: Apr 22

Wiring Diagrams: Chapter 2


Basic Symbols


In this module, we will introduce you to some of the basic symbols you will find on a wiring diagram. Skip to quiz!


The Legend


A symbol on a wiring diagram represents a specific electrical component within the circuit. Before you can learn how to read a diagram, you must understand what each symbol represents.


Recall that wiring diagrams include a legend. The legend explains what certain symbols on the diagram represent. The legend does not explain what every symbol means.

The picture to the right shows the legend of a wiring diagram. You can see that each line of the legend is made of a symbol and a description. The symbol is what you will see in the diagram. The description is what that symbol means.


For example, look at the first symbol on the legend. The first symbol shows a thin solid line. Next to the line, it says “factory power wiring”. Any thin solid lines you see on a diagram are factory power wiring.


Symbols


Recall that a resistor is a component that reduces the current and voltage flow through a circuit. A zig zag symbol represents a resistor on a wiring diagram. You can see the resistor symbol in the picture to the right.


Recall that a capacitor is used to store electrical energy within a circuit. A “-|(-” symbol represents a capacitor on a wiring diagram. You can see an example of the capacitance symbol in the picture to the right.


Recall that there are two types of capacitors:

  • Polarized capacitors, and

  • Non-polarized capacitors

Polarized capacitors have a positive and a negative end. Non polarized capacitors do not have a positive and a negative end.


In the picture to the right, you can see the symbol for a polarized capacitor. The polarized capacitor has a “+” sign and curved lines.


In the picture to the right, you can see the symbol for a non-polarized capacitor. The non polarized capacitor is on the left side of the picture. It has two straight lines and no “+” sign.


An inductor is a coil that stores electrical energy in the form of magnetic energy. A spiraling line on a wiring diagram represents an inductor.


Recall that there are two types of current: AC and DC. AC and DC power supplies will have different symbols.


A power supply is a device that supplies power to the system. The symbol for an AC power supply is a circle with a wave in it.


The symbol for a DC power supply is a circle with a “+” and “-” sign within the circle.


A switch is a device that can disconnect or complete the flow of current in a circuit.


There are two symbols used for switches on a wiring diagram:

  • A symbol for an open switch,

  • A symbol for a closed switch

The symbol for an open switch is a straight line between two circles. The line is not touching both circles.


The symbol for a closed switch is a straight line between two circles. The line is touching both circles.


On a diagram, you will see switches in open or closed states. If the diagram shows an open switch, the switch should be open for the circuit to function. If the diagram shows a closed switch, the switch should be closed for the circuit to function.


In this module, you learned the electrical wiring symbols for common elements on a wiring diagram. The legend will define certain symbols on the diagram. It is important to memorize symbols so that you can quickly and effectively read basic wiring diagrams.


In the next module, we will go through some more complex circuit symbols.



Complex Symbols


In this module, we will introduce you to some of the symbols you might see a on complex wiring diagram. Skip to quiz!


The Legend


Recall that wiring diagrams use symbols to indicate a specific electrical component. Before you can learn how to read a diagram, you must understand what each symbol means.

Recall that wiring diagrams include a legend. The legend lists what some symbols on the diagram represent.


For example, the picture to the right shows the legend of a wiring diagram. You can see that each line of the legend has a symbol and a description. The symbol is what you will see in the diagram. The description is what that symbol means.


Symbols


Recall that a contactor is a relay used for higher current circuits.

Contactors have two states:

  • Closed

  • Open

You can see the symbol for a closed contactor switch in the picture to the right. Recall that the controls within a circuit can open or close switches.


You can see the symbol for an open contactor switch in the picture to the right.


Contactors will be shown in an open or closed state on the wiring diagram. The state of the contactor on the diagram is the state the contactor must be in for the circuit to work. For example, if the diagram shows an open contactor then the contactor must be open for the circuit to function.

A relay is a type of switch. A controller can remotely open or close a relay. For example, a thermostat turning on a heater is an example of a relay. The thermostat sends a signal to the relay to open or close. The relay opening or closing turns on the heat.


You can see an example of the relay symbol in the picture to the right.


A transformer is an electrical device that transfers voltage and current between circuits.


Recall that an overload switch is used to protect a circuit from surges in current/voltage. The symbol for an overload switch looks like two C’s touching.


A high pressure switch opens the circuit when too high of a pressure is detected. It is common to find high pressure switches in HVAC units.


A low pressure switch opens the circuit when the system has too low of a pressure.


Some switches have a time delay between opening and closing. A switch with a time delay will have a vertical line into the switch and a branch at the bottom. The branch at the bottom indicates that it is a time delay switch.


The symbol for a motor is a circle with an M in the middle of it.


The symbol for a winding is a spiraling coil. Windings can be found within components like motors or compressors.


Recall that a fuse is a device used to protect circuits from surges in current or voltage. The symbol for a fuse looks like a wave symbol (~).


Lines between symbols on a diagram represent wiring. Dashed and solid lines represent different types of wiring on a diagram. The legend will have a definition for each type of wiring in a circuit.


Field wiring is wiring that the technician or installer must do in the field. A dashed line represents field wiring on diagrams.


Factory wiring is wiring that the factory has done before they sold the product. You do not need to wire anything that is labeled factory wiring. A solid line represents factory wiring on a diagram.


We have covered a lot of symbols. What should you do if you forget one? Generally, the best method is to google wiring diagram symbols. There are images on Google that show common wiring diagram symbols.


In this module, you learned some of the complex symbols you will see on a wiring diagram. It is important to memorize these symbols so you can quickly read a diagram.



Question #1: There is only one type of capacitor.

  1. True

  2. False

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Answer: False

There are two types of capacitors. Capacitors can be polarized or non polarized.


Question #2: A polarized capacitor will have a “+” and a “-” at each end of the capacitor.

  1. True

  2. False

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Answer: True

True, a polarized capacitor has a positive and a negative terminal. The + and - sign will mark which end of the capacitor is positive or negative.


Question #3: A circle with a wave (~) inside the circle represents an AC power supply.

  1. True

  2. False

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Answer: True

True, an AC power supply will have a circle with a wave inside of it. Recall that the ~ symbol means AC current.


Question #4: A DC power supply will have a circle with a “+” and a “-” sign in the circle.

  1. True

  2. False

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Answer: True

True, a DC power supply will have a circle with a +/- in the center. The +/- represents the polarity of a DC power supply. Recall that DC current only flows in one direction so each component has a positive and negative end.


Question #5: An open switch has two circles with a line that does not touch both circles.

  1. True

  2. False

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Answer: True

True, the symbol for an open switch is two circles with a line between them. If the line touches both circles, then the switch is closed. If the line does not touch both circles, it is open.


Question #6: Contactors have two symbols: one for an open contactor and one for a closed contactor.

  1. True

  2. False

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Answer: True

True, contactors can be shown in two states on a wiring diagram. The contactor symbol can show that the circuit is open or closed.


Question #7: The position of the contactor in the diagram is the position the switch must be in for the circuit to function properly.

  1. True

  2. False

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Answer: True

True, the symbol for the contactor on the diagram represents the position the contactor must be in for the circuit to function correctly.


Question #8: What components will you find windings in?

  1. Motors

  2. Compressors

  3. All of the above

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Answer: All of the above

You will find windings inside of motors and compressors.


Question #9: Field wiring is wiring that:

  1. A technician must perform in the field

  2. The manufacturer wired

  3. Can be ignored

  4. All of the above

Scroll down for the answer...
















Answer: A technician must perform in the field

Field wiring is wiring that the technician must perform in the field. Generally, a dashed line represent field wiring.


Question #10: Factory wiring is wiring that:

  1. A technician must perform in the field

  2. The manufacturer wired

  3. Can be ignored

  4. All of the above

Scroll down for the answer...












Answer: The manufacturer wired

Factory wiring is wiring that the manufacturer has done. The technician does not need to worry about wiring factory wiring. Generally, a solid line represents factory wiring.


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