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Wiring and Circuits (2019)
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Wiring and Circuits (2019)

Simple Switches

Electrical systems should be set up so they can be turned on and off easily. This is helpful to people who use the system, but also important for safety.

On / Off Switch

A simple switch (technical term: SPST switch) has two terminals. When the switch is ON, it conducts electricity across them. When the switch is OFF, it does not.

To understand how a switch works, use a multimeter and test the connections by touching the leads to the legs of the switch.

Click to reveal steps
Testing Wires with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Checking Continuity

A multimeter can be used to test for an unbroken electrical connection between two points. Something with no breaks is called "continuous", so this process is called "continuity" testing.

Selecting Continuity Testing Function

The continuity testing function of the multimeter tests for electrical continuity between two points that you touch the multimeter's leads to.

Tip: If there is a continuous connection, the multimeter will make a beep sound, so the icon for this mode usually looks like a "sound waves" symbol.

  • Some multimeters do not include this feature. If yours does not, follow the steps below but use the lowest-value Resistance test feature (Ω) on your multimeter instead, and instead of a beep, look for a resistance value of zero or near zero to be shown on the screen.
Safety Notice

The continuity tester does not work on circuits that have power running through them. Disconnect power from the portion of the circuit you are testing and test the parts individually. The multimeter may be damaged if you attempt to use this feature on a powered circuit.

Step 1: Plug black lead into multimeter

Plug the black lead of the multimeter into the COM terminal.

Step 2: Plug red lead into multimeter

Plug the red lead of the multimeter into the terminal with one of the following icons next to it:

  • Continuity Symbol Continuity Symbol
  • Ohms Symbol Resistance (Ohms) Symbol
  • Voltage (Volts) Symbol Voltage (Volts) Symbol
  • Diodes Symbol Diodes Symbol

Tip: The continuity test feature is electrically similar to several other multimeter functions, so it usually shares a plug and a spot on the dial with one of them. Different multimeters have it share with different modes.

Step 3: Turn dial to Continuity Testing setting

Turn the dial to the connectivity testing setting.

Some multimeters, like the orange one shown, have multiple functions on a dial setting. You may need to press the FUNC or function button to switch the multimeter to the connectivity testing setting. Look for the connectivity symbol on the screen of the multimeter.

Step 4: Touch leads together

Touch the metal parts of the multimeter leads together. The multimeter should make a sound while they are in contact (because the two leads are electrically connected to each other).

  • If no sound is played, check your connections and try again.
Step 5: Touch the leads to the wire

Touch the two leads to the ends of the wire you want to test. If you hear a sound, it means that there is a continuous electrical path between those two points.

  • This means there is no connection between the two points. Try to narrow down where the problem is by testing shorter portions of the wire. For instance, try touching the leads directly to the conductor in the wire -- if that part passes, then the problem must involve one of the connectors.
  • This either means you are trying to test for continuity across a component like an LED that cannot be tested using this mode (use Diode test mode instead), or it means the connection is loose.
  • The connector may be not be tightly crimped onto the wire conductor. Try tightening it.
  • You may also have damaged the conductor itself while attaching the connector -- for instance, you might have accidentally cut into the conductor while removing the wire insulation. This generally cannot be repaired, and you should remake that portion of the wire.
Step 5: Touch the legs of the switch in the ON position

Flip the switch to the ON position, and test for continuity across the terminals. There should be an electrical connection when the switch is ON, so the multimeter should beep.

Step 6: Touch the legs of the switch in the OFF position

Flip the switch to the OFF position, and test for continuity across the terminals. There should NOT be an electrical connection when the switch is OFF, so the multimeter should remain silent.

Step 7: Turn dial to Off

Turn the multimeter dial back to the OFF position when you are done.

Mini Project Adding a Switch

Adding a Switch
Project Goal:
  • Insert the switch into your existing simple LED circuit so that electricity will have to flow through it for the circuit to be complete. It should look like the example above when completed.

How To: Prepare Spade Connectors

Follow along with this module to prepare wires with spade connectors

Click to reveal steps
Attaching SPST Switch: Required items and tools

To begin attaching and crimping spade connectors, you will need the following:

  • 16 AWG Wire 16 AWG Wire
  • Wire Cutter / Stripper 1Wire Cutter / Stripper
  • Spade Connectors Spade Connectors
  • Toggle Switch Toggle Switch
  • Phillips #2 Screwdriver Phillips #2 Screwdriver
Step 1: Prepare wire for spade connectors

The switch will need to be connected on both ends, so prepare two wire-ends to have connectors crimped on to them. Make sure you have enough length of wire.

Step 2: Expose the conductive core

You will need to expose a small amount of the conductive metal inside the wire on each end. Do this by cutting off a small portion of just the plastic insulation around the wire on both sides.

  • If you need to expose more conductor, use a wire cutter.
  • If you have a wire cutter with gauge holes, find the hole that matches the size of wire you have, place the wire through the hole, and squeeze the handle firmly. Twist the wire back and forth until the insulator is cut, and the conductor slides out smoothly.
  • If you have a wire cutter without gauge holes, place the cutting head where you want to trim to, and cut "around" the outside by squeezing the blade down gently on the outside of the insulator, and rotating the blade and wire back and forth to saw through the insulation without damaging the conductor inside.
  • If you have too much conductor, use a wire cutter to cut off the excess length.
Step 3: Complete wire preparations

Your wire should look similar to this, with about a quarter inch of exposed conductive core.

Spade Connectors

Spade connectors make a mechanical and electrical connection to the wire when the metal loop inside the crimp area is squeezed down onto the conductor.

Connecting Spade Connectors

The "spade" side of the connector will typically go around a metal screw, and the screw will be tightened down on top of the spade to create both a physical and electrical connection.

Step 4: Insert conductive core into spade connector

Insert the exposed conductor through the small loop on the back of the spade connector.

Tip: Twist the ends of the conductor strands so they stay together more easily.

Step 5: Insert connector and wire into crimper slot

Insert the loop + conductor into the slot on your crimper that matches the size of the loop.

Step 6: Crimp the connection

Firmly squeeze the handle of the crimper to press the loop closed around the conductor. Many crimper designs will not open back up until you have squeezed far enough -- if the crimper won't open, keep squeezing until it does.

Tip: You can squeeze harder if you grip toward the ends of the handles.

Tip: If you really need the crimper to open early, there is usually a small release latch inside the handle.

How To: Test Spade Connectors

Follow along with this module to test your spade connector's connection

Click to reveal steps
Testing Wires with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Checking Continuity

A multimeter can be used to test for an unbroken electrical connection between two points. Something with no breaks is called "continuous", so this process is called "continuity" testing.

Selecting Continuity Testing Function

The continuity testing function of the multimeter tests for electrical continuity between two points that you touch the multimeter's leads to.

Tip: If there is a continuous connection, the multimeter will make a beep sound, so the icon for this mode usually looks like a "sound waves" symbol.

  • Some multimeters do not include this feature. If yours does not, follow the steps below but use the lowest-value Resistance test feature (Ω) on your multimeter instead, and instead of a beep, look for a resistance value of zero or near zero to be shown on the screen.
Safety Notice

The continuity tester does not work on circuits that have power running through them. Disconnect power from the portion of the circuit you are testing and test the parts individually. The multimeter may be damaged if you attempt to use this feature on a powered circuit.

Step 1: Plug black lead into multimeter

Plug the black lead of the multimeter into the COM terminal.

Step 2: Plug red lead into multimeter

Plug the red lead of the multimeter into the terminal with one of the following icons next to it:

  • Continuity Symbol Continuity Symbol
  • Ohms Symbol Resistance (Ohms) Symbol
  • Voltage (Volts) Symbol Voltage (Volts) Symbol
  • Diodes Symbol Diodes Symbol

Tip: The continuity test feature is electrically similar to several other multimeter functions, so it usually shares a plug and a spot on the dial with one of them. Different multimeters have it share with different modes.

Step 3: Turn dial to Continuity Testing setting

Turn the dial to the connectivity testing setting.

Some multimeters, like the orange one shown, have multiple functions on a dial setting. You may need to press the FUNC or function button to switch the multimeter to the connectivity testing setting. Look for the connectivity symbol on the screen of the multimeter.

Step 4: Touch leads together

Touch the metal parts of the multimeter leads together. The multimeter should make a sound while they are in contact (because the two leads are electrically connected to each other).

  • If no sound is played, check your connections and try again.
Step 5: Touch the leads to the wire

Touch the two leads to the ends of the wire you want to test. If you hear a sound, it means that there is a continuous electrical path between those two points.

  • This means there is no connection between the two points. Try to narrow down where the problem is by testing shorter portions of the wire. For instance, try touching the leads directly to the conductor in the wire -- if that part passes, then the problem must involve one of the connectors.
  • This either means you are trying to test for continuity across a component like an LED that cannot be tested using this mode (use Diode test mode instead), or it means the connection is loose.
  • The connector may be not be tightly crimped onto the wire conductor. Try tightening it.
  • You may also have damaged the conductor itself while attaching the connector -- for instance, you might have accidentally cut into the conductor while removing the wire insulation. This generally cannot be repaired, and you should remake that portion of the wire.
Step 6: Turn dial to Off

Turn the multimeter dial back to the OFF position when you are done.

How To: Attach Spade Connectors

Follow along with this module to attach the spade connectors to the switch

Click to reveal steps
Attaching Spade Connectors

The spade terminals on the wire connect to screw-down terminals on the switch. They are called this because they are literally screws that smash the spade connectors down to hold them in place.

Step 1: Loosen screws on switch

To attach the spade, first loosen the screws by turning them counterclockwise.

Step 2: Insert spade connector

Slip the spade connector underneath the screw head when there is enough room.

Step 3: Tighten screw on switch

Then, tighten the screw by turning it clockwise until the screw is firmly in place.

How To: Prepare Alligator Clips

Follow along with this module to create alligator clips

Click to reveal steps
Alligator Clip Connector: Required items and tools

To begin crimping clips, you will need the following:

  • Alligator Clip Alligator Clip
  • Wire Wire
  • Alligator Clip Crimper Alligator Clip Crimper
  • Wire Stripper Wire Stripper
Step 1: Prepare wire for alligator clip

Take the end of the wire, and make sure there is enough conductor exposed to attach the connector -- about 1 cm, or half an inch is good for this type of clip.

  • If you need to expose more conductor, use a wire cutter.
  • If you have a wire cutter with gauge holes, find the hole that matches the size of wire you have, place the wire through the hole, and squeeze the handle firmly. Twist the wire back and forth until the insulator is cut, and the conductor slides out smoothly.
  • If you have a wire cutter without gauge holes, place the cutting head where you want to trim to, and cut "around" the outside by squeezing the blade down gently on the outside of the insulator, and rotating the blade and wire back and forth to saw through the insulation without damaging the conductor inside.
  • If you have too much conductor, use a wire cutter to cut off the excess length.
Step 2: Insert conductive core into alligator clip

Insert the exposed conductor through the small loop on the back of the alligator clip.

Note: If the connection is too loose, strip off some more of the insulator and fold the conductor together to create an extra "thick" wire for the alligator clip slot.

Tip: Twist the ends of the conductor strands so they stay together more easily.

Step 3: Insert clip and wire into crimper slot

Insert the loop + conductor into the slot on your crimper that matches the size of the loop.

Step 4: Crimp the connection

Firmly squeeze the handle of the crimper to press the loop closed around the conductor. Many crimper designs will not open back up until you have squeezed far enough -- if the crimper won't open, keep squeezing until it does.

Tip: You can squeeze harder if you grip toward the ends of the handles.

Tip: If you really need the crimper to open early, there is usually a small release latch inside the handle.

Step 5: Crimp both sides

To ensure the fit is good on all sides, rotate the connector 90 degrees, and squeeze the handle closed again.

Step 6: Complete alligator clip crimping

The alligator head connector should now be securely attached to your wire!

How To: Test Alligator Clips Connection

Follow along with this module to test your alligator clip's connection

Click to reveal steps
Testing Wires with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Checking Continuity

A multimeter can be used to test for an unbroken electrical connection between two points. Something with no breaks is called "continuous", so this process is called "continuity" testing.

Selecting Continuity Testing Function

The continuity testing function of the multimeter tests for electrical continuity between two points that you touch the multimeter's leads to.

Tip: If there is a continuous connection, the multimeter will make a beep sound, so the icon for this mode usually looks like a "sound waves" symbol.

  • Some multimeters do not include this feature. If yours does not, follow the steps below but use the lowest-value Resistance test feature (Ω) on your multimeter instead, and instead of a beep, look for a resistance value of zero or near zero to be shown on the screen.
Safety Notice

The continuity tester does not work on circuits that have power running through them. Disconnect power from the portion of the circuit you are testing and test the parts individually. The multimeter may be damaged if you attempt to use this feature on a powered circuit.

Step 1: Plug black lead into multimeter

Plug the black lead of the multimeter into the COM terminal.

Step 2: Plug red lead into multimeter

Plug the red lead of the multimeter into the terminal with one of the following icons next to it:

  • Continuity Symbol Continuity Symbol
  • Ohms Symbol Resistance (Ohms) Symbol
  • Voltage (Volts) Symbol Voltage (Volts) Symbol
  • Diodes Symbol Diodes Symbol

Tip: The continuity test feature is electrically similar to several other multimeter functions, so it usually shares a plug and a spot on the dial with one of them. Different multimeters have it share with different modes.

Step 3: Turn dial to Continuity Testing setting

Turn the dial to the connectivity testing setting.

Some multimeters, like the orange one shown, have multiple functions on a dial setting. You may need to press the FUNC or function button to switch the multimeter to the connectivity testing setting. Look for the connectivity symbol on the screen of the multimeter.

Step 4: Touch leads together

Touch the metal parts of the multimeter leads together. The multimeter should make a sound while they are in contact (because the two leads are electrically connected to each other).

  • If no sound is played, check your connections and try again.
Step 5: Touch the leads to the wire

Touch the two leads to the ends of the wire you want to test. If you hear a sound, it means that there is a continuous electrical path between those two points.

  • This means there is no connection between the two points. Try to narrow down where the problem is by testing shorter portions of the wire. For instance, try touching the leads directly to the conductor in the wire -- if that part passes, then the problem must involve one of the connectors.
  • This either means you are trying to test for continuity across a component like an LED that cannot be tested using this mode (use Diode test mode instead), or it means the connection is loose.
  • The connector may be not be tightly crimped onto the wire conductor. Try tightening it.
  • You may also have damaged the conductor itself while attaching the connector -- for instance, you might have accidentally cut into the conductor while removing the wire insulation. This generally cannot be repaired, and you should remake that portion of the wire.
Step 6: Turn dial to Off

Turn the multimeter dial back to the OFF position when you are done.

Mini Project Adding a Switch (continuation)

Adding a Switch

The main difference is that, instead of connecting the LED to the + side of the battery direction, the LED wire goes to one end of the switch, and the battery goes to the other. That is, the switch is "between" the battery and the LED.

Explanation

A switch is a mechanical device that moves a piece of conductive material so that it completes a circuit when it is in one position, and breaks the circuit when it is in another position.

Old switches were literally a piece of metal that would be pressed down to connect circuits.

Old Switches
Old Switches

This is why switches in a circuit diagram are typically illustrated as as a piece of wire that flips up and down to complete or break a circuit.

Open and Closed Switch
Open and Closed Switch

This setup wasn't very safe (the full amount of electricity in the circuit would literally flow through the metal piece you were touching), and it was inconvenient to have to hold the switch in place. Modern switches are constructed using different materials and mechanical arrangements to accomplish the same thing, but more indirectly.

Old vs. New
Old vs. New

When the switch is in the OFF position, no electricity flows through it, which means that there is not a complete electrical path through your setup. The LED does not light.

When the switch is ON, the electrical connection is complete, and the LED lights up.

Check Your Understanding

Which of the following does a simple (SPST) switch do? Choose all that apply!
  • Allow electricity to flow when it is in the ON position
  • Allow electricity to flow when it is in the OFF position
  • Prevent electricity from flowing when it is in the ON position
  • Prevent electricity from flowing when it is in the OFF position
  • Allow electricity to flow only in even increments
Which of the following are good reasons to use a switch in a circuit? Choose all that apply!
  • To allow someone to easily power or de-power the circuit by hand
  • To make the circuit conduct more electricity
  • To allow the circuit to be turned off quickly in case of an emergency
  • To allow the circuit to store energy and run even without the battery
  • To allow the circuit to controlled remotely

Try It: Reverse Switch Direction

Does the direction of a switch matter?
Try reversing the direction of the switch: swap which spade goes to which terminal on the switch.
What happens?
  1. The direction of the simple switch does not matter, because the switch simply makes the electrical connection complete or incomplete. It's like a wire being present or missing, and wires have no direction.

Try It: Two Switches

Can you connect two switches in a row?
Wire a second switch into your circuit next to the first one, as shown above.
What happens?
  1. Both ON: The circuit is complete, and the LED lights up.
  2. Either one OFF: The circuit is not complete, because either switch can break the pathway. The LED stays off.
  3. Both OFF: The circuit is not complete, and the LED stays off.

Other Types of Switches

The "simple" switch in this lesson is technically called a "Single pole, Single throw" (SPST) switch.
Other types of switches include Double Pole Switches and Double Throw Switches.

Double Pole Switches

  • "Poles" are the number of circuits that are affected by the switch.
Your simple "single-throw" switch affects one circuit.
  • Double pole switches are used to open or close two circuits at once.
They therefore have four connectors instead of two: one pair for each circuit to be completed or broken.
  • Flipping the switch connects both circuits (ON) or breaks them both (OFF) at the same time.
  • Some switches have more than two poles, meaning they affect more than two circuits at the same time.
  • EXAMPLE: Indicator Panel Lights: The switch controls a large, high power circuit. It also controls a status light in an instrument panel that says when the switch is ON. The light is small, and would be damaged if it were hooked up to the high energy circuit. A double-pole switch is used to flip both the main circuit and the small indicator light circuit together, without electrically connecting the two.
Indicator Panel Lights
Indicator Panel Lights

Double Throw Switches

  • "Throws" are the number of positions the switch has that complete a circuit.
Your simple "single-throw" switch has one position that closes a circuit (the "OFF" position doesn't close any, it leaves the circuit open).
  • Double throw switches have two positions that complete circuits.
  • Instead of switching between ON (open) and OFF (closed), the switch toggles between completing two different circuits.
Poles and Throws
Poles and Throws
  • A "double throw" switch can also have an OFF position that connects to none of the potential circuits.
  • Some switches have more than two throws. For instance, a rotary switch can have many throws.
Toaster Over Switch
Toaster Over Switch
  • EXAMPLE: Multimeter Dial: Each "function" on a multimeter is actually a different circuit. The dial on the front of the multimeter is a many-throw switch -- one for each function (plus OFF). When you turn the dial to a function, it powers the circuit for that function, and leaves the other circuits open.
Toaster Over Switch
Toaster Over Switch

Complex Switches and Names

  • Some switches connect multiple circuits, AND have multiple positions.
Switch types commonly use abbreviated names based on the number of poles (circuits affected) and the number of throws (positions).
  • "Single pole, single throw" = SPST
Affects one circuit, has one ON position (and one OFF position)
  • "Single pole, double throw" = SPDT
Affects one circuit, has two ON positions (plus one OFF position)
  • "Double pole, single throw" = DPST
  • "Double pole, double throw" = DPDT
  • "Triple pole, single throw = 3PST
  • And so on...

How to Identify Switch

  1. Count the number of connections on the "left hand side" of the circuit diagram: how many circuits are opened or closed together when the switch is flipped. This is the number of poles.
  2. Count the number of connections on the "right hand side" of the circuit diagram for each pole: these are circuits that can be connected to, based on the position of the switch. This is the number of throws.
Poles and Throws
Poles and Throws
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