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3-Way Switch Wiring Explained

Electrical

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March 1, 2023

3-Way Switch Wiring Explained. How Three-way light switches work. In this presentation we’ll learn how to control a light using a 3-way switch, which is convenient when there are two or more entrances to a room, or an upper and lower stairwell. We’ll show several different wiring configurations.

To watch the FREE YouTube version of this presentation, scroll to the bottom or click on the following link. 3-Way Switch Wiring Explained

Electrical Safety Warning

Whenever working with electrical be sure to shutoff the power at the electrical panel, and hire a qualified electrician to do the installation if you are not confident that you can do the job safely. Electricity can kill.

3-Way Switch for Controlling a Light or Fan

How do 3-Way Light Switches Work?

If we look at a 3-way switch, we’ll see that it has four terminal screws. We have two traveler terminals, which are usually identified by their light color of bronze or copper, a ground terminal in green, and a common terminal often a dark color. A 3-way switch won’t have an on/off designation that can be found on standard switches, as either position could be on or off.

Within the switch either one of the traveler terminals is connected to the common terminal, which can make or break the circuit depending on the position of the other switches traveler terminal matching or not. Its like the game of concentration where you turn over two playing cards trying to get them to match. When the two separate 2-way switches match on their traveler wires the light goes on, when they don’t match the light goes off. They can match with both on red or both on black, but not black/red or red/black.

The two traveler terminals can be on the same side of the switch or on opposite sides of the switch depending on the switch manufacturer.

Checkout these 3-Way Switches

3-Way Switch Example #1

With this layout we have the light fixture between the two switches.

The incoming electrical power will connect to the common terminal of switch #2. Then we route the Black traveler wire for switch #2 to switch #1. We do the same thing for the Red traveler wire. From the common terminal on switch #1 we connect to the light. We bring in the neutral wire from the power source and connect directly to the light. We also bring in the ground wire from the electrical panel and connect to each of the switches.

If we remove the switch covers and look inside we can see how these 3-way light switches work. Inside is a single pole double throw switch which provides each switch with an option to connect the common terminal with either the red or black traveler terminal.

When both switches are not in the same configuration, such as shown below we have one switches common connected to a black traveler and the other switch connected to a red traveler terminal. If we follow the power from the source, the black common wire from the electrical panel connects to the common terminal on switch #2, then passes through the switch to the black traveler terminal and then onto switch #1 where it dead ends.

3-Way Switch Wiring with switches in opposing positions

If we flip switch #1 to the black traveler wire then the light comes on as the electrical circuit has a complete path through both switches to the light.

The process of turning on and off the light can occur from either switch, as we show here we now flip switch #2 to break the electrical circuit and shut the light off. In order to turn the light back on we have two options, we can flip switch #1 to the red traveler terminal so that it matches switch #2, or just flip back switch #2 to the black traveler terminal.

3-Way Switch Example #2

Depending on the layout of the space and where the wiring originates from, there are several versions of how the wiring can be done. We’ll show how to wire a 3-way switch with both switches wired before the light.

Will install a light fixture, and two switches. From the power source we’ll bring the black hot wire to switch #2 common terminal. Note, that this wire is usually black, but your wire could be another color.

Then we’ll run a black traveler wire from 3-way switch #2 to the same terminal on switch #1, this could be from left side of the switch to the left side of the other switch. Then we install an outlet box and run the black wire from the dark common terminal screw on the bottom of switch #2 to the light fixture. Now we have one complete path from the source all the way to the light.

Next, we install a red traveler wire from the right side of switch #1 to the right side of switch #2. This gives us a second optional path to the light through the red traveler wires from the black hot wire brought to the common terminal.

Checkout these 3-Way Switches

Next, we install the incoming white neutral wire which is usually white, and we connect to the light fixture. Then we install the green ground wire from our source to the outlet boxes ground terminal, and then to each of the ground terminals on the switches. The ground is usually an insulated green wire or can be bare copper wire. In the fixtures electrical box there should be a place to land the ground wire.

We have 4 wire connections on each switch. Two travelers, one common, and one ground.

When we turn on the power and both switches have the same traveler terminal connected to common then the light will come on as shown above where both black traveler wires are in the same position. This could be either both black or both red travelers in the same position.

When one of the switches is flipped so as there is no matching traveler wire that provides a complete path to the hot common wire the light goes off as shown here with switch #1 being flipped off. The 3-way switch doesn’t indicate the light is on when the switch is in the up position, and off when in the down position. The light being off or on is determined when there is a matching pair of traveler wires that provide a complete path for the power to the light.

Inside the 3-Way Switch

If we looked inside we could see that each switch has a single pole and a double throw, meaning that the switch has two options, to either have the common connected to traveler terminal #1 or 2.

When both of the switches are on the same traveler terminal as shown here, the power runs through to the light. If either of the switches changes position then the light will go off. The electrical power comes through the black common wire connected to switch #2, and uses the red wire to reach terminal #2 on switch #1, where it flows through the common wire to the light, making a complete circuit.

Stairwell Example

First we mount a light above or stairwell and install a switch at the top and bottom of the stairwell. We bring in power using a black wire and connect to the common terminal on switch #1.

From switch #1 we run a black traveler wire to switch #2’s traveler wire terminal, and from the common on switch #2 we run a black wire to the light fixture. Then we run a red, second traveler wire from switch #1 to switch #2. We install a neutral wire from the electrical panel to the light fixture. Lastly we provide a green insulated ground wire from the panel to each of the light switches.

3 way light switch

How Steam Traps Work

MEP Academy Instructor

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February 22, 2023

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How Steam Traps Work. We’ll explain the important job of steam traps and how the three most common steam traps work. We’ll also show you examples of where they’re used in the HVAC industry.

if you prefer to watch the video of this presentation scroll to the bottom or click on this link. How Steam Traps Work.

When steam gives up its heat it turns into condensate, which must be removed from the system. The rate of heat transfer through the heat exchanger is highest when the heat exchanger is full of steam. If condensate wasn’t drained out of the system, and it collected in the heat exchanger, then the rate of heat transfer would drop.

Remember that a pound (0.45 kg) of water or condensate holds 1 Btu (1.5 kj) as it gives up its heat one degree (0.55 K), and that steam gives out approximately 1,000 Btus (1,055 kj) for every pound (0.45 kg).

IThe Heat Content of Steam vs Condensate

if condensate is allowed to sit in the heat exchanger the system will lose capacity. Therefore, it’s important to make sure that the condensate is quickly removed while not allowing the steam to escape without first transferring its heat.

Condensate Water Hammer

Condensate if left to collect in the pipes could cause problems such as water hammer noises, where a high velocity slug of condensate water is slammed against fittings or equipment. This is like a tidal wave in the pipes. The energy is dissipated onto the piping components and is noticeable by the noise it makes or the rattling of the pipes.

When the steam boiler starts the system will be full of air and non-condensable gases that need to be vented out of the system. If a steam trap fails to remove air from the system, the air and non-condensable gasses will reduce the heat transfer rate of the heat exchanger. Non-condensable gases behave like an insulator, thereby reducing the heat transfer rate.

The steam traps job is to remove condensate, air, and non-condensable gases, while preventing steam from leaking past it in a steam system. For the basic understanding of a steam system see our video on Steam Heating System Basics.

There are three main types of steam traps, but they all require a differential pressure between the inlet and the outlet of the steam trap. We’ll cover how each of the three steam traps categories work.

Mechanical Steam Traps

The density difference between the steam and condensate is how a Mechanical steam trap works. Steam in the form of vapor is less dense than that of liquid condensate which makes the use of a float as an effective means of control. The float and thermostatic (F&T) trap and the inverted bucket trap are the two most common mechanical steam traps. These traps use floats that rise, and fall based on the amount of condensate, and either open or close the trap.

Float and Thermostatic Steam Trap – Mechanical Steam Trap

When the condensate level is high in a float & thermostatic trap, the float rises and opens the trap to allow condensate to flow out. When the condensate level drops, so does the float which causes the trap to close.

With an inverted bucket trap, steam will push the bucket upward closing the trap, while condensate will pull the bucket down opening the trap.

These steam traps open and close based on the density of the steam and condensate being different. With the F&T trap the heavier condensate lifts the float, while with the Inverted Bucket the heavier condensate sinks the float.

Thermostatic Steam Traps

The temperature difference between steam and condensate is how a thermostatic steam trap work. It’s based-on temperature. After the condensate forms its temperature drops below that of the steam, and after a certain drop in condensate temperature the trap opens. When steam first condenses its temperature is the same as the condensate. This will require that the condensate cool further before the trap opens.

There are various substances used as the controlling element in thermostatic steam traps, such as fluids and metals.

The bimetal type thermostatic steam traps uses the differing coefficients of expansion of various metals. When two metals are attached together, and one expands at a different rate then the other based on temperature, this can be used to open and close a steam trap. As more and more steam enters the trap, the bimetal heats up and expands while pulling up on the stem of the valve that closes the steam trap, and when it cools down it opens the trap. The presence of steam will cause the bimetal to bend in a certain direction and close the trap, while the cooler condensate will contract the bimetal to open the trap.

When the boiler starts up after being off, the air, condensable gases, and the condensate in the system will be pushed through the open steam trap.

Thermodynamic Steam Traps

The Velocity difference between steam and condensate is how a thermodynamic steam trap works. Steam moves at a greater velocity than condensate. The only moving part in this thermodynamic steam traps is the disc, which moves up and down, opening and closing the port for condensate to flow through.

When the steam system is started, the cool condensate and air is pushed by pressure into the trap, causing the disc to move upward, allowing the condensate and air to pass through.

As hot condensate moves through the steam trap some of it flashes into steam, causing the pressure to drop below the disk, which causes the disk to drop.

As the condensate heats up and flows through the trap it cause steam to flash under the disc, which drops the pressure causing the disc to drop lower towards the seat or opening. As this is occurring the flash steam on top of the disc is pushing the disc closed. This traps the flash steam in the upper chamber, which causes an equalization of pressure on both sides of the disk, preventing any more condensate from passing through.

Flash steam in the upper chamber condenses, causing the disc to be forced up, while allowing condensate to enter. This process repeats itself over and over again.

How Steam Traps Work

Steam Heating System Basics

MEP Academy Instructor

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February 15, 2023

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Steam Heating System Basics. Learn how steam systems work and where they’re used in the HVAC Industry. We’ll show you three systems that use steam for heating.

If you prefer to watch the Video of this presentation, than scroll to the bottom or click this link. Steam Heating System Basics.

Steam heating systems are found in Commercial, Residential, and Industrial Facilities. They can be found in central plants of large University Campuses and in District Steam Distribution systems.

Steam is used in laboratories, breweries, food processing, industrial plants, in hospitals for sterilization, and in the production of electricity through steam driven turbines. There are two basic system types, direct and indirect steam systems.

We’ll discuss the basic indirect steam heating system.

Steam is moved through the system of pipes by the pressure created when water is vaporized into steam. There are no pumps required, as the higher pressure within a steam system causes it to move through the pipe, valves, and equipment.

We can witness this on any stovetop when a tea kettle whistles. As the water turns to steam it seeks to escape the tea kettle through the small opening and whistles as it escapes.

Condensate from the steam condensing needs to be brought back to the system for reuse unless the steam is used for a process. The condensate can be brought back by gravity or with the use of a condensate return pump.

When heat is added to water its temperature will rise until it hits the point of evaporation, at this point it changes from a liquid into a vapor or steam. This occurs at 212 Fahrenheit or 100 degrees Celsius at normal atmospheric pressure.

If we enclose the water within a steam boiler with no opening to the atmosphere, the steam will increase the pressure within the system as the molecules move faster and faster, colliding into each other and the walls of the boiler looking for a lower pressure escape route like the hole in the tea kettle.

If we connect piping to an opening in the steam boiler the steam will exit the boiler into the piping without the need of a pump, but just by the pressure created by the steam.

Steam Heat Exchanger for Heating Hot Water

Here we use a steam boiler to feed the primary side of a heat exchanger. The steam will transfer heat to the secondary loop which is feeding the heating hot water coils in Air Handlers. The steam gives up its latent heat and condenses as the heat is transferred to secondary side of the heat exchanger.

Steam Heat Exchanger serving a Heating Hot Water Coil

To make sure that we are not letting steam into the condensate return we install a steam trap. The steam trap prevents steam from passing through and only lets condensate through. See our video on How Steam Traps Work for a explanation of steam trap types.

On the secondary side of the heat exchanger is a separate loop of water that serves to heating the air in the building air handlers.

If we look inside the heat exchanger, we can see that the primary and secondary piping never mix. The steam enters the heat exchanger as steam and leaves as condensate, while the secondary loop heating hot water is moved by a pump through the system.

The secondary loop heating hot water return enters the bottom of the heat exchanger and picks up heat from the steam and leaves through the top to the air handlers heating hot water coil.

The steam boiler doesn’t need a pump as the molecules are moving fast and exerts pressure on the walls of the boiler and when the piping is connected to the boiler than pressure pushes the steam out of the boiler and into the pipes just like a tea pot that is boiling, and the steam is escaping out of the spout whistling as it exits.

Now we’ll add another piece of equipment requiring a supply of steam.

We’ll have to redo the steam piping to make connections to the domestic system. We’ll install a new steam main and make a connection to the Heat Exchanger making sure to come off the top of the steam main, which we’ll explain why in a minute. Next, we’ll connect the domestic hot water heater and storage tank.

We’ll need a steam trap at the end of any main steam run to allow only condensate to pass through. A main condensate pipe needs to collect all the condensate from any steam systems, here we show a simple system.

Next, we’ll connect the condensate from the heat exchanger to the main condensate line and be sure to install a steam trap to prevent steam from escaping. Allowing steam to escape would be a waste of energy. We’ll also connect the condensate from the heat exchanger that feeds the domestic hot water system and include a steam trap.

We need to connect the main steam line through the steam trap to the main condensate piping going back to the boiler.

Now we can feed the building with domestic hot water, including a return line, and makeup water. This completes a simple layout of a steam heating system. Of course, there are many other components to a steam system which we’ll cover in a more advanced video on steam heating, but this gives you a simple view of what it might look like.

Why Tap Steam off the Top

It’s important that any steam branch line be taken off the top of the main steam pipe in order to prevent pulling condensate into the branch. As you can see the steam will rise to the top because of its lighter density and higher temperature.

Steam should be taken off the top of the Main and Condensate off the bottom. — Steam off the top of the Main and Condensate off the bottom.

For similar reasons you want to make any condensate branch connections off the bottom of any steam line or system to ensure that you are only pulling condensate. And all condensate branches should contain some type of steam trap to ensure that only condensate passes through to the condensate system.

Why use Steam?

Steam has a higher heat content then hot water, which means it can carry a lot more heat in a smaller volume. This heat is in the form of latent heat, which is the change in state from liquid to vapor, and from vapor to liquid. This helps keep the pipes smaller. Steam is water based, so its non-toxic nor flammable, although it’s very hot and will need insulation on the distribution piping to avoid heat loss and prevent someone for getting burned if touched.

The main components of a steam system are the steam boiler, the distribution piping, the steam traps, and the heat exchanger or equipment that requires the use of steam. There will need to be a source of fuel, such as natural gas or fuel oil. A means for makeup water supply, and for boiler blow down to remove unwanted dissolved solids.

This is the basics of a steam system. We’ll get into the details of how each of these components work in other videos.

Steam Heating System Basics

How Solenoid Valves Work

MEP Academy Instructor

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February 8, 2023

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How Solenoid Valve Work. We’ll discuss how Solenoid Valves are constructed and how they work in a typical mechanical system. We’ll explain where they’re commonly used in refrigeration and air conditioning systems, and why.

If you prefer to watch the video of this presentation, scroll to the bottom or click this link How Solenoid Valves Work

The main purpose of a solenoid valve is to automatically control the flow of fluids and gases. Solenoid valves use electromagnetism to electrically control the opening and closing of valves. They serve an important function in the automatic control of refrigerants, water, natural gas and other liquids in the HVACR industry.

Checkout these Solenoid Valves here

Where are Solenoid Valves located?

Solenoid valves are in many systems besides the HVAC industry, but we’ll keep our discussion to the Mechanical Construction Trades. Here are some examples of where you might find solenoid valves.

Water-Source Heat Pumps and AC Units

Various energy codes require that flow to a water-cooled heat pump or AC unit be shut off when not operating during normal business hours. This prevents additional pressure drop on the pump when the water-cooled Air Conditioner isn’t operating. The condenser water flow to the non-operating compressor is stop by the controls sending a signal to the solenoid valve to close.

Water-Source Heat Pump System with ASHRAE 90.1 Shutoff Requirement using a Solenoid Valve

ASHRAE 90.1 2019, section 6.5.4.5.1 states “Each hydronic heat pump and water-cooled unitary air conditioner shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off”.

ASHRAE Standard 90.1-2019 The use of a Solenoid Valve for Compliance

Refrigerant Pump Down

Solenoid valves are used for the automatic pump down of refrigerant systems. This is done by placing a solenoid valve in the liquid line before the expansion valve. See our other video for explanation on How Electronic Thermal Expansion Valves Work.

When the thermostat is closed upon a rise in temperature the solenoid is energized causing it to open and allow refrigerant to flow through the normally closed solenoid valve to the expansion valve. The refrigerant entering the evaporator causes a rise in pressure that triggers the controller to turn the compressor on. When the thermostat is satisfied and cooling is no longer required, it stops the flow of electricity to the solenoid valve, causing it to close.

The compressor keeps running, pulling the refrigerant out of the low side and into the high side liquid receiver.

When the suction pressure gets too low, before it reaches a vacuum, the low-pressure safety switch will shut off the compressor to prevent it from burning out. The pressure-sensitive controller will turn on and off the compressor based on suction pressure.

Checkout these Solenoid Valves here

When choosing solenoid valves for refrigerant systems, the engineer will use the refrigerant type, the tonnage, and the Maximum Operating Pressure Differential as the selection criteria. Manufacturers provide tables for selection of their solenoid valves.

Hot Gas Bypass

To prevent the evaporator coil from freezing during low load conditions, a bypass is routed from the hot gas discharge of the compressor to the low side of the system right before entering the evaporator. Bypass is controlled by a Hot Gas Bypass Valve that maintains a minimum evaporator pressure to prevent freezing of the coil.

During a pump down cycle, you don’t want this valve to interfere with lowering the evaporator pressure, so a solenoid valve is installed ahead of the Hot Gas Bypass Valve. When the pump down cycle is initiated, the solenoid stops the flow to the Hot Gas Bypass Valve preventing it from bypassing hot gas into the evaporator.

The use of Hot gas Bypass is considered old technology, as it’s more energy efficient to use multiple compressors or variable capacity compressors.

How do Solenoid Valves Work?

An electrical coil within the solenoid valve housing creates an electromagnetic field when energized. The magnetic field induces the opposite polarity in the metal plunger which can be made of iron or steel. Because opposite magnetic poles attract, the plunger will be pulled up into the coil within housing causing the valve to open.

If electrical power remains supplied to the coil, the valve will remain open. This is how a normally closed valve works. When the coil is de-energized the magnetic field disappears and the plunger falls by gravity, or a spring pushes the plunger to close the valve. The coil can use line or low voltage power to be energized.

So, it’s the magnetic field that operates the valves and creates the valve to open.

Solenoid valves are available in the normally open or normally closed position. The designation of normally open or normally closed applies to the position of the valve with no power applied, hence its normal position.

Normally Closed Solenoid Valves

The normally closed solenoid valve is the more commonly used form. The normally closed solenoid valve opens when power is applied to the solenoids coil windings. When no electrical power is applied the valve will remain closed.

Normally Closed Solenoid Valve - Valve will open when energized — Normally Closed Solenoid Valve – Valve will open when energized

With a normally closed valve the spring keeps the valve closed when no electricity is applied to the coil. When the coil receives power, the magnetic field induces an opposing magnetic charge to the plunger causing it to be pulled upward into the heart of the magnetic field, opening the valve.

When the power is shutoff the magnetic field disappears allowing the spring to push the plunger downward closing the valve.

Solenoid Valve – Normally Open

The normally open solenoid is always open until power is applied to its coil windings. This is the type used for refrigeration pump down, as you want the flow of refrigerant to be unhindered until its time to activate the solenoid valve and force closed the valve.

Normally Open Solenoid Valve. Valve closes when energized.

When power is applied to the coil it pushes the plunger downward instead of pulling upward. This causes the plunger to close the valve. When power is shutoff to the coil, the spring will force the plunger upward opening the valve.

How Solenoid Valves Work

Electrical Safety Warning

How do 3-Way Light Switches Work?

3-Way Switch Example #1

3-Way Switch Example #2

Inside the 3-Way Switch

Stairwell Example

Condensate Water Hammer

Mechanical Steam Traps

Thermostatic Steam Traps

Thermodynamic Steam Traps

Steam Heat Exchanger for Heating Hot Water

Why Tap Steam off the Top

Why use Steam?

Where are Solenoid Valves located?

Water-Source Heat Pumps and AC Units

Refrigerant Pump Down

Hot Gas Bypass

How do Solenoid Valves Work?

Normally Closed Solenoid Valves

Solenoid Valve – Normally Open

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