What is an Automatic Transfer Switch?

Everything You Ever Needed To Know About Transfer Switches

Transfer switches: What do they do? What types are there? What’s necessary for your project? Our full and comprehensive guide to literally everything you needed to know about transfer switches.

When it comes to generators, whether you’re an electrician, install generators for a living, or a DIY’er that just needs to get things done on a budget, chances are, you’ll be in the market for a transfer switch.

Now let’s fill in the gaps on the physics and fundamentals of these electrical control powerhouses.

In this article we’ll go over:

  • What is a transfer switch?
  • What do transfer switches do?
  • What are the benefits of using transfer switches?
  • What types of transfer switches are there?
  • How to pick one that’s right for your application?
  • And much more.

Keep reading to learn everything you ever wanted to know about these electrical commanders —which, we realize for some of you, may not be much! Having said that, if you’re someone who’s amped up about the idea of learning more, this piece is for you.

Warning: this article contains extensive use of acronyms. Best to keep a notebook handy to jot them down. Be forewarned.

Onto the article.

Transfer Switch Basics

The Canadian Electrical Code (CEC) defines a transfer switch as “actuates upon failure of the normal power supply, must control the emergency power supply.”

That doesn’t tell us much about transfer switches. Here’s our simpler, more helpful definition:

Transfer switches, also known as electrical switches, are the directors of the electrical world. They’re devices that automatically (or manually) transfer, or switch, from a primary power supply source to a backup source when there’s a power outage.

Phew! That’s better. With us so far? Good.

Now let’s define a transfer switch in more detail.

What is a transfer switch?

Transfer switches are devices that look like big metal boxes. More specifically (and seriously), these metal boxes are your building’s electrical supply controllers. They’re a bit like your home’s panelboard but they direct larger amounts of power.

What exactly does this mean, though? What do these switches do and how do they do it? Let’s find out.

What does a transfer switch do?

Transfer switches are used to redirect electrical circuits during a power outage. A transfer switch panel allows you to restore power, usually by using a generator, to critical circuits when utility power is no longer available. This ensures a near-continuous source of power for things like:

  • Production lines and machinery
  • Heating systems
  • Fire alarm systems
  • Industrial refrigeration
  • Commercial air conditioning (AC) systems

Similarly, in a residential home, a transfer switch will transition electricity from the grid to a generator to power things like:

  • Lights,
  • Powerpoints (think a portable AC unit),
  • A sump pump,
  • Essential medical equipment (if applicable), and
  • Hard-wired equipment like appliances (fridges, stoves), hot water systems, furnaces, etc.

Where can generator transfer switches be used?

Transfer switches are important parts of the electrical inner workings of:

  • Farms
  • Factories
  • Data centres
  • Hospitals
  • Long-term care facilities
  • Universities and schools
  • Water treatment plants
  • Organizations and small businesses, like restaurants
  • Telecommunication facilities
  • Electrical plants (ironically) and other types of power plants.

What happens when power to these buildings is lost? Mayday!

Thank goodness for transfer switches. They can use their powers to redirect electricity where it’s needed most. For example:

  • Maintain life-support systems in a hospital,
  • Keep livestock health and productive,
  • Feed a solar or wind farm active in the event of poor weather
  • Sustain freezers at a pharmaceutical manufacturing facility that store vaccines and medications.

What’s the source of these powers? More on this next.

What supplies power to a transfer switch?

Transfer switches would be useless metal boxes without a secondary energy supply. The source of that energy, or electricity, can come from:

  • An electrical (or power) generator, or
  • Other external device that feeds a current to the switch

When power goes out to a building, an electrical generator is told by a transfer switch, Hey—you’re on! It then feeds power to the building’s panelboard which it then sends to external devices.

A transfer switch can be installed indoors or out. It may look different depending on whether it’s powering a huge factory, school, or hospital but its main parts are the same.

We’ll cover those parts in another section.

Up next: we give examples of some of the major types of transfer switches.

What are the different types of transfer switches?

There are different brands like ASCO Power Technologies, Cummins Inc., and Thomson Power Systems  but in general there are three different types of transfer switches:

  1. Automatic transfer switches (ATS)
  2. Manual transfer switches (MTS)
  3. Non-automatic transfer switches (NATS)

We’ll cover all three of those, plus some of their varieties. Let’s begin with one of the most popular types: the automatic transfer switch.

1 Automatic transfer switches (ATS)

As the name implies, Automatic Transfer Switches (ATS) do their thing automatically. Everything is done instinctively with this type of transfer switch.

When the power goes out, maybe only for a couple of seconds, the trusty transfer switch senses this and automatically tells the generator, “Quick! You’re on!” (Get it?) The switch then transfers the power source to your business or home from the electrical grid to the generator.

When the power comes back, the switch does its thing automatically again by disconnecting the power from the generator, transferring it back to the grid, and turning off the generator.

The automatic transfer switch then patiently waits for the next power outage so it can do its thing all over again.

Why you should use an Automatic Transfer Switch (ATS)

We weren’t being fair earlier when we called transfer switches metal boxes. Switches are important pieces of protective equipment that keep people, buildings, and the environment safe from:

  • Freezing temperatures (due to loss of heat in a home or building)
  • Power leaks
  • Energy loss
  • Lost capital

Where that last point is concerned, think about what happens when the power goes out at home. You scramble to save every piece of meat, fish, and other frozen items from your freezer box.

The same goes for stores, restaurants, offices, or public service buildings. Imagine the loss of money and the chaos a loss of power to a senior’s residence, a hospital, or a meat packing plant would cause. Transfer switches are an indispensable part of a building’s electrical system.

(We’re sorry, transfer switches, for any disrespect we may have shown you earlier in this post.)

To learn about the parts of an ATS, visit our website [https://www.primapowersys.com/].

Up next: we’ll cover one example of an ATS, the bypass isolation transfer switch.

Bypass isolation transfer switches

A bypass isolation transfer switch (BITS) is a type of ATS that comes with two switching mechanisms instead of one. This offers redundancy in emergency situations for critical uses.

In short, no pun intended, an ATS redirects electrical power to the system, while the BITS bypass acts as its backup.

BITS are used by:

  • Healthcare centres
  • Long-term care facilities
  • Government institutions
  • Power plants and other critical facilities
  • Media companies and data centres
  • For ATS testing or maintenance purposes

To top off this section on ATS’s, we’ll describe one last type of automatic switch: the service entrance-rated transfer switch.

Onto our second switch type on the list: manual transfer switch.

2 Manual transfer switches (MTS)

A Manual Transfer Switch (MTS) has to be, you guessed it, activated manually.

In the event of a power outage, a manual switch needs to be hand-operated by a real person in order to swap a building’s electrical grid to a backup power source. If no one is around to activate the switch, the power source isn’t reassigned and electricity stays off.

Not good if you have a hotel full of guests!

Not all manual switches are right for every application. How, then, can you ensure you’ve picked the right one in the event of a power emergency?

Answer: it’s all about how much phenomenal cosmic power a switch can handle. Read on to learn what we mean.

How to pick the perfect manual transfer switch

Have you ever blown a fuse? Not the emotional kind, the electrical kind. There was a voltage problem behind that cruel joke. Too much power went into the system and—Bam!—a fuse blows to protect it.

Similarly with switches, you’ll need the right device to handle the right amount of power. When picking a manual transfer switch, first:

  1. Determine the wattage you need to run your generator, then
  2. Pick a switch rated to that wattage (normally anywhere between 30 to 3,000 amps), and finally
  3. Choose a switch that has a built-in wattage metre (optional).

(A friendly note: Don’t despair if you don’t know what those electrical terms mean. We added them in to make us sound smarter. For those savvy readers who do, you’re welcome.)

And finally, we’ll introduce our third and final type of transfer switch: the nonautomatic transfer switch.

3 Non Automatic transfer switches (NTS)

At first glance, Non Automatic Transfer Switches (NTS) sound just like manual switches. Anything that isn’t automatic has to be done by hand, right?

Yes and no.

The term NTS is reserved for electrically operated switches. 

  • Like the manual versions, they’re incapable of self-initiating when there’s a power outage—they need human intervention to work.
  • Unlike manual switches, they’re equipped with nifty electronic controls that manage everything about the power redirect once the main transfer has occurred.

These types of switches offer the following bonus features:

  • They monitor power source characteristics like voltage and frequency
    • They make sure power can only be moved over to a new source when all these specific characteristics are met—perfect in situations when a forced manual transfer is too risky.
  • The ability to be controlled remotely.

The remote perk is perfect for situations where access to a physical switch is limited or dangerous to personnel.

Next up, we’ll cover the types of transfer switch transitions, or the ways in which they can switch between one power source to another.

What are the different types of transfer switch transitions?

What are transfer switches used for exactly? Sure, we’ve already established they’re in charge of redirecting a power when the main source fails but how do they do this exactly?

How does a transfer switch transition power from one piece of equipment to another?

There are two main ways:

  • Open transitions, and
  • Closed transitions

Keep reading for a breakdown of the differences between these ATS transition types.

Open transition transfer switches (OTTS)

Open transition transfer switches (OTTS) affectionately have what’s called a “break-before-make” switch function.

This means that:

  • The transfer switch breaks the connection to the original, main power source …
  • …before it makes a connection to the secondary power source first (usually to a generator) before switching off the connection with the utility source, and then

The flow of electricity is therefore interrupted for a split second.

Open transition switches are generally the most popular and affordable options out there because they’re generally compatible with the largest number of applications.

Closed transition transfer switches (CTTS)

In contrast, closed transition transfer switches (CTTS) work in the opposite way. They use a “make-before-break” switch function.

This means that:

  • It makes a connection to the secondary power source first (usually to a generator) before switching off the connection with the utility source, and then
  • Once it’s established it’s safe to do so, it breaks the connection to the original, main power source.

With these switches:

  • Both the primary and secondary power sources (the utility and the backup/generator) are allowed to overlap briefly which …
  • … avoids a momentary power loss that often goes along with OTTS systems.

Now that we’ve gone over the what, why, and how of transfer switches, let’s cover what’s in them.

What makes up a transfer switch?

Transfer switches are made up of many fancy parts used to operate its inner workings.

A switch’s main components include:

  • An enclosure
  • The transfer mechanism
  • Transfer logic controller
  • A communications metre and instrumentation

Let’s go over each one of these in more detail next.

The transfer switch enclosure

The enclosure of a transfer switch is the metal skeleton that houses all its other parts. Remember the metal box we mentioned earlier? The frame is what we were talking about.

This part protects the inner workings from:

  • The elements, if outdoors, and
  • From regular wear-and-tear and other forms of damage (if indoors or out).

The size and configuration of the board depends on the number and load, or amount of energy, it has to power.

The transfer switch mechanism

The main structure of the board will house, among other things, the transfer switch mechanism

This is the rockstar part of the switch because it’s responsible for doing the power switching.

In most cases, transfer switches are mounted close to a wall for safety reasons. They’re more secure that way, plus electricians and technicians can more easily access their inner workings this way. A front facing board is the norm although there are exceptions depending on:

  • Spacing,
  • Maintenance needs, and
  • Installation obstacles.

Do you know what’s at the front of a transfer switch that runs the switch mechanism? Controls. We cover these next.

Transfer logic controller

The transfer logic controller is an electronic controller that stores operating data, monitors the condition of the power sources, and initiates transfer sequences.

Along with the controller, there’s also a fancy spot on the front of the switch that provides information about what’s going on with the switch.

Read on to find out more about the communications metre.

Communications metre and instrumentation

Everything you need to control the phenomenal cosmic power (!) of a transfer switch is located on its front panel.

On the metre, you’ll find indicators that communicate any data an electrician or technician would want to know about the state and the workings of the switch.

Specifically, you’ll find information about:

  • Power availability
  • Potential indicators
  • Voltmetres
  • Malfunction gauges
  • Energy usage displays
  • And many other pretty lights and buttons in fancy colours.

Now that we know what makes up a transfer switch, let’s chat in more detail about the benefits of using them.

What are the benefits of using transfer switches?

Here are some of the main advantages to using transfer switches:

  • Reliable and uninterrupted power supply

Transfer switches ensure you never lose power when your primary source of electricity is lost. That makes power reliable.

Downtime can be very costly. A loss of power could mean lost revenue when your business can’t stay open or from lost product.

Reliability means profitability and safety.

  • Simple to use

Once an automatic transfer switch has been properly set up, you don’t need to worry about anything. It required a quick setup by a professional and will work for years.

  • Safe to use

As much as a properly functioning transfer switch can save lives, it’s also equally safe to use.

Since there isn’t much to do after it’s set up, you can rest easy knowing your power supply will keep people safe during and inbetween power outages.

How to care for and maintain a transfer switch?

We might be biased but we’ll say it anyway: the best way to care for and maintain your transfer switches is by hiring a professional to do it for you.

As we hope we’ve demonstrated in this article, switches are complex pieces of equipment that manage a large amount of electricity. At the very least, a poorly maintained switch can mean a loss of power in an outage. While this isn’t always the worst thing in the world, it’s a nuisance.

At the worst, a poorly maintained switch can mean a loss of resources, money, and, in very extreme cases, serious accidents and even death.

Even a wish from a magic genie can’t protect you from a broken or poorly maintained transfer switch!

This isn’t the time for a DIY solution. Best leave the upkeep of your generators and switches to the pros. You, your assets, and those you depend on you to keep power flowing will thank you.

How do you know what type of transfer switch is best for you?

When it comes to maintaining power to a hospital, utilities plant, or other essential services building, now’s not the time to play a guessing game.

The easiest way to figure out which type of transfer switch to use for your residential or commercial building is to work with a professional.

A consult with a pro is well worth the investment. It can save you time, money, and frustration when it comes time to choosing and installing the right switch for your needs.

What about caring for your existing switches? Pros are the best option here, too.

Where Can I Install My Generator?

There are a number of things to consider when choosing a location for a home backup generator. There are installation instructions and local code requirements which dictate where the generator can be placed in relation to a building and other surrounding objects. Local code requirements can vary by region so it’s important to be familiar with the requirements in your area. There are local bylaws which inform people about minimum distances away from neighbour properties and maximum noise allowances which influences where you can place your generator. In addition to local code requirements, following the manufacturer’s recommended installation instructions is extremely important to maintain a safe, professional installation of your power generation system. Failure to do so could void the manufacturer’s warranty and could potentially lead to hazards such as objects or building fires. Some considerations to follow highlighted in the installation instructions are minimum distances away from objects and buildings, minimum distances away from the exhaust output, and minimum distances from openings and/or vents. There also needs to be space left for technicians or maintenance people to service the generator effectively. While you need to satisfy all the safety requirements, you want to place the generator as close to the utility connections as possible. This minimizes the distances for wire and piping which lowers the risk of connection problems and reduces installation costs.

In addition to considering the proximity of objects and structures relative to the generator, you also need to consider the ground on which the generator is placed. In most cases, you’ll need to create a smooth, level surface to place the generator on. Typically, this can be done by pouring a concrete pad or by purchasing a prefabricated mounting pad supplied by the generator manufacturer. While your generator is designed to withstand the outdoor elements, it will need to be placed in areas of your property where water does not commonly pool or snow does not tend to build up. Choosing an appropriate location for your generator will improve the performance of your generator.

There are many safety factors that need to be considered when choosing a location for your generator. As a licensed electrical contractor with many years of experience installing residential generators, a representative of Prima Power Systems can help guide you through the process. We will take care of all permitting and ensure that the installation meets local electrical code requirements to avoid any fines and/or relocation costs. Give us a call today to get started on your home improvement project.

What is the Difference Between Mobile, Portable, and Towable Generators?

The terms “mobile” and “portable” for generators are ambiguous and could mean multiple things. Sometimes those terms refer to an inverter generator, larger gasoline powered generator, a truck mounted generator, or generator attached to a trailer (towable). Mobile or portable generators could encompass any power generation unit that is not specifically bolted down and stationary.

Portable Generators

That said, portable generally refers to a generator that can be moved by one person. It might have wheels to help maneuver or be light enough and have a handle to carry.

An inverter generator is a type of portable generator. The Cummins Onan P2500i is about 50 pounds and has a carry handle built into the casing. It’s a digital inverter generator that runs on gasoline, and offers 2,200 running watts, capping out at 2,500 watts.

The Cummins Onan P4500i offers more power with 3,700 running watts, peaking at 4,500 watts. It’s also a digital inverter gasoline generator. The P4500i weighs about 98 pounds, but has wheels and a telescopic handle, like a big suitcase, to make it easy to move around. 

Industrial Portable Generators

When someone says portable, they could also be referring to an industrial portable generator, which could be used on a jobsite, like Winco’s lines of Dyna Professional and Big Dog generators. These generators range from 104 pounds to 504 pounds and can be mounted on a four-wheel dolly for increased maneuverability. These generators typically have a lifting eye built into the frame. This lets you use mechanical assistance, such as a forklift or crane, to lift it in or out of a truck or trailer. The Winco line offers watt capacities (starting/running) of 3000/2400W up to 22000/19000W.

Mobile & Towable Generators

Towable generators are portable as well, but they are fastened to a trailer to tow behind a vehicle. Towable generators generally range from 20kW to 500kW. These generators can be run in parallel for additional power. Paralleling generators refers to connecting two or more generators together to increase output. Towable generators are ideal for worksites (local or remote), events, unexpected outages, and scheduled outages. 


Since the terminology is confusing, you can just give us a call to discuss what you need. You can review some specification sheets at the links below, but a Prima Power Systems rep will be happy to answer any questions and help you find a generator that meets your needs.

You can find the spec sheets for our portable generators at these links:

Winco Portable Generators

Atlas Copco Mobile Generators

Doosan Portable Generators


How Much Power Do You Need in a Generator?

The amount of electricity that a device needs to operate is measured in watts or kilowatts (1,000 watts). Most devices display their power needs on the plate or label where the model number and serial number are located. It might be stated as a single number, like 2900; or it may have two numbers, like 3500/2900. The two numbers means that the device needs more power to start up, in this case 3,500; but less power to continuously operate, the 2,900.

Generator specification sheets show the power of the generator. This is the maximum capacity of the generator in kilowatts. That number needs to be at least as high as the total needs of all of the devices you need to power at one time.

Residential Generators

In residential applications, it is important to follow the Canadian Electrical Code (CEC) in order to correctly size a generator for the desired electrical loads. This can vary from a whole home backup system, to a smaller system that only powers a few essential devices. While sizing for a smaller isolated system is quite simple, a whole home system will require the load calculation guidelines set forth by local governing safety authorities. The guideline starts with a base load demand calculated by the square footage of the dwelling followed by calculating the electrical needs of items such as stoves, air conditioners, and dryers, etc. From there, any other type of heating or motor loads must be added and calculated at the full rating of the device.

Startup vs Operational

The start up requirements vs the operational requirements are determined by how the generator will be used. For example, if you are using the generator as the prime power source for an industrial operation at a remote site, your total startup needs might be 400 kilowatts (kW), and your operational needs 310kW. If all of the equipment has to be started at the same time, then your generator needs to be at least 400kW. But, if you can start up each piece of equipment in a series, and the most power you need for any one piece of equipment is 200kW, then your total needs will be somewhere between 310kW and 400kW. In the example below, Equipment 1 (E1) needs 200kW to start up, so it’s started first. E1’s needs then drop to 150kW. To keep E1 going while we start E2, we need a total of 270kW, then it drops to 250kW. To keep E1 and E2 going while we start E3, we need 330kW. So, our total needs are 330kW and not 400kW.

  Start Operate Start Next Maintain
E 1 200 150   150
E 2 120 100 270 250
E 3 80 60 330 310
Total 400 310    


Let’s look at the opposite end of the scale, a portable generator for your tools. If you’re only using one tool, then you only need enough power to start the tool, as the power maintenance requirements are always lower. 

For a backup generator for your home, business, or industrial facility, you need to add up the kilowatts needed for each item you need to power at the same time. So, for example, at a restaurant, if a power outage occurs, you’ll need backup power for the refrigerators, freezers, the heating, cooling, and exhaust systems, the payment system, and at least some emergency lighting. You’ll also want all of those items to startup as soon as possible to avoid interruptions. If you add up all of those energy needs, you’ll end up with the number of kilowatts you’ll need at one time. Let’s say that number is 85kW. Then you’d choose a generator that has a capacity of at least 85kW.

Now, let’s talk about voltage. Voltage is the amount of force with which the electrical energy leaves the generator to travel through the electrical system. The amount of energy decreases as it travels. The more force it starts with, the less energy is lost along the way. In practical terms, your voltage needs will differ depending on the distance and overall amount of space you need to cover. A home, for example, can do with a lower voltage than a large factory. The higher voltage for the factory will ensure that the item farthest away from the generator will get the power it needs, and the overall distribution will be more efficient. 

If power requirements are expressed in amps instead of kilowatts, you can use this formula to convert between them: Watts = Volts x Amps.

You don’t need to worry about doing all of these calculations yourself. We’re here to help, and will be happy to review your needs and make a recommendation. Just give us a call at 1-604-746-0606 or contact us today.

What is a Generator?

A generator (or genset) is a machine consisting of two main parts: an engine and an electrical generator. The engine component converts fuel into mechanical energy and the electrical generator component converts mechanical energy into electricity. Other components usually include an engine speed regulator, voltage regulator, alternator, and a cooling and exhaust system. The alternator is required to produce AC (alternating current) power, which is what is supplied to our homes and is needed for most appliances and equipment.

Different Types of Generators

While large generators, such as those used by utility companies to produce power for a community, may use water, wind, or coal, most of the generators we sell generate electricity by burning a fuel, such as gasoline, natural gas, or propane, or a combination of these. We provide prime and standby generators, portable generators, towable generators, and PTO generators. 

Power Take Off Generators

A PTO generator is a bit different in that it uses the engine from a vehicle like a tractor, so it doesn’t need its own fuel source. PTO’s are an attractive option for farmers, since most already have a tractor, and without its own engine, PTO’s are more affordable.

Mobile, Portable, and Towable Generators

Many portable generators also have an inverter. The inverter counteracts the reduction in the speed of the engine when a load is connected (e.g., a power tool). The inverter allows a consistent output of electricity. Inverter generators are also quieter and more fuel efficient because the engine runs at fewer revolutions-per-minute (RPMs) compared to other engine generators.  

Why Have a Generator

Our generators can serve as the primary source of power or as a backup system when the usual source of power is disrupted.

All electrical devices, from a curling iron to a washing machine, to a HVAC system for a large facility, require a certain number of watts to start up and to stay on. Motor loads have a higher startup power requirement than running requirement and can take up to three times as much power to start than a running load. Wattage needs depend on what you want to provide electricity to. 

The smallest generator we sell weighs about 50 pounds, while the largest is more than 40,000 pounds. Power output from standard generators range from 2,500 watts to 2,000,000 watts (2,000kW); however, we can configure multiple generators to work in parallel to produce even more electricity at one time.

Since we offer a variety of different generators, our website categorizes them by type of use. Click on any category below to view the options:

If you’d like to read more about the different types and usages for generators, these articles are also available:

Of course, you can also just give us a call at 1-604-746-0606. We’re here to help you make an informed decision and are happy to discuss your needs and answer your questions.


What Kind of Generator Do You Need?

You know you need power and you know why, but where do you start when selecting a power generator? In this article, we’ll look at the different categories of generators, where they are commonly used, and some of the options to consider.