Saturday, October 1, 2016

Introduction to Switch Wiring

Within these articles are instructions for understanding 27 different residential switch wiring methods used by Construction Electricians in the U.S. (120 volt) With photos, wiring diagrams and descriptions of single pole, 3way, and 4way methods. 
  • If you only need one switch to control a light, go here>   single pole switch wiring
  • If you need 2 switches to control a light, go here>   3 way switch wiring
  • If you need three switches to control a light, go here>   4 way switch wiring
  • If you still need more switches just add 4ways. Need six switches? Use two 3ways with four 4ways. Weather you use one 4 way or more, the 4 ways are always wired in between two 3 ways.

  Understanding Current Flow In A Switch Circuit   

The more you understand how electricity finds its way through a circuit, the easier it will be to make complex switch wiring connections.

Consider how electricity flows through the wiring in a simple flashlight circuit. 
Tiny electrons leave the batteries and press against the switch. When the switch is closed, they flow through the switch and enter the light bulb pushing through it's small filament wire out through the socket returning to the batteries. 

The current passes through the 2 batteries and starts all over again, following the same path over and over until the switch is opened, breaking the metal to metal contact and stopping the flow of electricity
The upper diagram shows a flashlight circuit. The switch is open, electrons cannot flow, the light is off.
The next diagram shows a light in a house with a wall switch connected to the utility transformer.
The key to understanding complex wiring is to learn how to identify or visualize the conducting path 

The circuit for a light in a house is very similar to the flashlight circuit. 

Power leaves Line 1 of the Utility transformer and flows through the main breaker, the circuit breaker, the switch, through the light and back to the transformer on the neutral. 

The current passes through the transformer and starts all over again, following the same path over and over from the transformer through Line 1 through the switches through the light and back on neutral until it is stopped by opening the switch or breaker
Line 2 could be used for another lighting circuit. 
Note that the top breakers in an electrical panel are labeled #1 and #2 and are both on Line 1 (phase A) Circuit breakers #3 and #4 are on Line 2 (phase B)

Here is another diagram of how electricity moves from the Utility transformer to a room light.

Electrical meters
Photo courtesy
A pole mounted transformer
.Photo courtes 

   DC and AC   
The Direct Current or DC in a battery powered flashlight circuit flows in one direction. The electricity in a house is AC or alternating current which flows in 2 directions alternating back and forth. In the first 1/120th of a second, the current of electrons are flowing in one direction from the hot to the neutral and the next 1/120th of a second current flows in the opposite direction from the neutral to the hot. All of this completes one cycle. There are 60 cycles in a second or 60 hertz (50 in Europe). 

It is common for electricians to talk about a electricity moving through a circuit as though it is DC moving in one direction from hot to neutral. Actually they are aware that it alternates and are addressing that first 1/120th of a second, when the electrons are frozen in time heading from hot to neutral. The red arrows, in the schematic above, show the direction of current flow during that first split second moment in time.

   Inside a switch   
It is important to understand which terminals are being connected and/or disconnected inside the switch when it's toggle is moved into a different position. The purple and red lines, shown below, identify the moving metal blades inside the switch, These blades make or break electrical connections between the external terminal screws identified here as black dots. The black lines that continue off the drawing represent electrical wiring.

S1) Two single pole switches, or S1's, are shown on the left.
In the top drawing the S1 is open and the light is off. The lower drawing shows the S1 closed the light is on. The internal blade pivots from one terminal screw. If the wires were swapped, this single pole switch would still function properly.
S3) Two 3ways or S3's are shown in the center drawings. Notice how the purple 3way switch blade pivots on the common terminal so that the common is always in contact with one of the 2 travelers and the travelers never connect together on the same switch. Of course we connect wires from the travelers on one S3 to the travelers on another S3 but here we are talking about the connections inside a 3way switch. And those connections inside never connect the travelers together.
 You could say that the only thing the 3way switch traveler terminals have in common... is the common.  (To determine if the light is on or off in the S3 or S4 drawing above requires a completed circuit drawing)

S4) At the right are two 4ways or S4's and they really do say IN and OUT on the back of the switch. The S4's shown here have the "IN's" on the top but some designs have the IN's on the side. Either way the inner metal blades (shown here in red and purple) always connect the IN's to the OUT's but never IN to IN or OUT to OUT. (There is no electrical connection between the red and purple blade where they cross in the top S4.)

So to review, when talking about the terminals on switches and there internal connections;
 The "traveler" terminals are never connected together by the internal blade.
 The "IN" terminals are never connected together by the internal blade.
 The "OUT" terminals are never connected together by the internal blade. 

Reading wiring schematics.

Wiring schematics are like road maps showing the routes that current will follow as it passes through the electrical wiring with symbols representing switches, lights and other items. Schematics are also an installation guide explaining how connections are to be made for proper operation.

The difficult part is transferring schematic plans to the real world. It is easy to look at a schematic and see a line that connects terminal C to a light. The hard part is trying to figure out where, in the real and 3 dimensional world, the light is and where terminal C is and how you are going to connect the two together with a wire. When professional electricians are confused about some complex switch wiring, they will make a rough schematic sketch to help them figure it out. 

Wiring schematics come in 2 different styles; Line diagrams and wiring schematics. 
 Line Diagrams are a simplified view of a circuit showing current flow from left to right, with the hot at the left and the neutral at the right.
 Wiring Schematics are more complex drawings that try to represent the positions of circuit items as they would be in the real world.

  Important Terms for Wiring Switches   

The "Common" or "C" terminal. Found only on a 3 way switch, the common is a single terminal screw that can connect to one traveler or the other.  
The common is like a hinge that swings the switch back and forth from traveler to traveler. Common to one traveler and then common to the other traveler but never connecting traveler to traveler. It is identified on the 3 way with the letter "C" or the word "common" and normally with a screw color that is different from the 2 traveler screws. The term "Common" refers to a common terminal screw only, not the wire connected to it. The wire connected to a common can be a hot feed or a switch leg. 
 There is no common on a 4 way switch or a single pole.

Feed.  Wiring with incoming electricity to provide electrical power with a Hot and a Neutral. 
"Incoming" Electrical Power, not "Outgoing" "Incoming" Electrical Power to a switch or a receptacle. Imagine you are about to plug together 2 extension cords. The cord in your left hand is plugged into an outlet so it is Hot and ready to Feed power to the cord in your right hand that is heading to your saw. Only the left hand cord is called the feed because it is "Incoming" The cord in your right hand would be considered the Load because it has the saw waiting to consume electricity.

 All the black wires that are continuously energized when the circuit breaker is on 
It is not a Neutral or a Switch Leg. The Hots will stay on even if a switch is turned off. With our extension cord example, only the black wire in both cords would be called a Hot. The extension cords are used here to represent 14/2 nm wire used in switch wiring. 

The term Hot  is also used to mean "energized"  
A switch leg can be Hot (temporarily energized) but not "a Hot" (continuously energized wiring) And a Hot cannot be a switch leg. Clear as mud?

Load.  Electrical items that consume electricity. 
A light is considered a load, it consumes electricity. TV's, fans, dishwashers these are all "Loads" Switches are not considered Loads. Switches are used to control electricity not consume electricity. (although dimmers do)

Neutral Wiring that is not switched and allows electricity to return back to the source. 
In switch wiring the neutral goes directly to the light, never to a switch. The neutral is a white wire that is paired with a hot. Not all white wires are neutral. A white wire used for a traveler is not a neutral but a switched hot. 

Pigtail. A 6 inch piece of wire connecting a group of wires to a terminal screw.
You might have 3 hot wires in a box that all need to tie together and your switch also needs a hot. All 3 will not fit under the switch terminal screw but one pigtail will. After the pigtail is added to the switch, all 4 (the 3 hots + the added pigtail) can be twisted together and capped with a wire nut.

Power.   Wiring with a 
Hot and a Neutral 
It is not controlled by a switch. It can refer to "incoming" or "outgoing" wiring. Both extension cords could be called Power. "This cord is Power from the panel and that cord is Power to the saw." Power is defined here as it is used in switch wiring not Ohms Law where it is defined as "electrical energy measured in watts"

Single Pole Switch   A switch with 2 terminals and 1 ground
Identified on blueprints as S1. When you only need one switch to control a light, use a single pole switch.  Only single poles are labeled "ON" and "OFF".

3 way Switch   A switch with 2 travelers, 1 common and 1 ground. 

Identified on blueprints as S3. When you need 2 switches to control a light, use two 3 way switches. The 2 traveler terminal screws are normally the same color and different from the common screw color.

4 way Switch  A switch with 4 traveler terminals and 1 ground 

Identified on blueprints as S4. If you need three switches to control a light, use tw3 ways with one 4 way.  The 4 way has 2 traveler terminals, of the same color, identified as "IN" and 2 traveler terminals, of a different color, identified as "OUT" The traveler wires from one 3 way connect to the "IN" terminals and the travelers from the other 3 way connect to the "OUT" terminals.

A common mistake with 4 ways is to take the 2 travelers from one 3 way  and connect one traveler wire to the "IN" and the other to the "OUT"

Switch leg. The wire that connects the switch to the light and becomes energized only when the switch is closed, flipped on. When the light is off the switch leg is dead. When the light is on the switch leg is hot.

Travelers. A pair of wires that connects 3way and 4way switches together.
Traveler wires connect to the traveler terminals. Travelers allow lights to be turned on or off at multiple locations. Electrical current will flow through one of the traveler wires until one of the switches is flipped.

Traveler terminals. A pair of same colored screws on a 3 way or 4 way switch where the traveler wires are connected. 

Electricity flows through the common terminal to only one of the traveler terminals until a switch is flipped then current flows through the common terminal to the other traveler terminal. Traveler terminals on a 4 way switch are labeled "IN" and "OUT" The traveler wires from one 3 way connect to the 2 "IN" terminals and the travelers from the other 3 way connect to the 2 "OUT" terminals.

Key Points

  • Switches are placed on the hot wire never the neutral wire. Switching the neutral allows a hot wire at the light even though the light is off (because the current cannot flow back on the neutral that is disconnected because of the switch.)

  • The code requires the metal frame on all switches to be grounded. Ground wires (not shown in this study) are twisted together along with a pigtail that is connected to the green ground screw on the switch.
  • A single pole switch is mounted so that the up position is "ON" and down is "OFF"  When a single pole switch is upside down the label will read "NO".
  • A 3way switch can be used as a single pole by using only one traveler terminal and the common. Be sure that the switch is in the up position when the light is on.
  • On 3 way and 4 way switches, properly identify your terminals by looking at the color of the screws and reading the terminal labels. Don't go by the terminal's position. Different manufacturing designs can re-position the terminal locations. 
  • The common is a single terminal screw that can connect to one traveler or the other. The 2 traveler terminals never connect together.
  • There is no common on a 4 way switch or a single pole.
  • Inside a 4 way switch, a connection is made from 1 "IN" to 1 "OUT" and another connection is made from 1 "IN" to 1 "OUT"  The 2 "IN" terminals never connect together and the 2 "OUT" terminals never connect together. 
  • There are no 4 way dimmers. Plan your wiring in a way that a 3way ends up where a dimmer is planned.