Home Generator Automatic Transfer Switch: Buyer’s Guide

Generators are a crucial investment for any home or business looking to secure themselves from the inconvenience caused by a power outage.

And like anyone who owns or is looking to purchase a home generator, you will come to understand that home generators require other additional equipment.  

One such additional piece of equipment is the transfer switch.

But what is a transfer switch? What are its uses? Why is it important? In this article, we offer you insight into all things related to generator transfer switches.

What is a Generator Transfer Switch?

A transfer switch is a permanent switch that is connected to your power box and helps to police the transfer of power load from the grid power to the generator.

Transfer switches also help prevent overlap of power between these two sources of power.

Some generators can run without a transfer switch.  However, this is dangerous.

When you’re using a generator without a transfer switch, there’s a possibility that when the power comes back to the main grid there will be two sources of currents powering your home.

 Budget Friendly Emergency Backup Power – Transfer Switch 

This will result in a power surge that may endanger utility workers and create the risk of electrocution, loss of equipment and appliances, and electrical fires. This is often referred to as back-feeding the grid.

Foregoing having a transfer switch also limits the number of devices that can be powered by the generator, and forces you to make do with extension cords.

Permanent sources of backup power are designed to automatically transfer power load during power outages.

This is, however, not always the case and some generators need a transfer switch manually installed.

You might be wondering which generators need transfer switches and which ones don’t. Standby generators, also known as portable generators, almost always need a transfer switch.

Unlike portable generators, standby generators are designed to keep power flow with minimal downtime during an outage.

 It is, therefore, necessary for standby generators to have a transfer switch for the transfer of power to be automatic between two sources.

Portable generators don’t necessarily need a transfer switch but it is still advisable to have one. It is also necessary to have a transfer switch if you have high-powered appliances with a massive load.

Types of Generator Transfer Switch and their Uses

Transfer switches are categorized based on their mode of operation. There are two main types of transfer switches; manual and automatic.

1. Manual Transfer Switches

Of the two types of transfer switches, manual switches are the simplest in terms of operation and design.

This type of transfer switch consists of a switching panel, power relays, and a single power cord running from the generator to the main power supply as the alternative source of power.

A manual transfer switch may also have circuit breakers to ensure safety by preventing overloading.

As suggested by the name, manual transfer switches work through manual intervention.

Therefore, in the event of a power outage, you have to manually switch it on for it to transfer power from the main power grid to the generator.

Once you manually pull the terminal on the transfer switch, the switch connection changes, energizing the relay and powering the switch connected to the generator.

Power continues flowing from the generator. Once the power is back, you also have to manually operate it to transfer the power source back to the main power grid and let the generator cool off before switching it off.

Manual transfer switches can handle electric currents ranging between 16 to 120 amperes.

For this reason, they are mostly used in homes and settings with low power needs. They are also often used with portable generators.

You should note that when working with manual switch transfer, there will be a definitive break and loss of power.

This is due to the time taken to transfer the power source from the main grid to the generator during power outages.

Types of Manual Transfer Switches (MTS)

Manual Transfer Switches

Although manual transfer switches are not diverse and they are of different types. These include; simple KITS, specified circuitry, rated load centers, single circuit, and standard switches.

Simple KITS: Are used for fast installation and switching often in homesteads and some commercial settings. This manual transfer switch consists of cables, power cords, and switches.

Rated Load Centers: Are usually a combination of load centers and transfer switches and are used as either the main panel or the subpanel. Rated load centers can provide enough power to between 38 to 40 circuitries.

Specified Circuitry: Only transfer backup power to intended circuits and only connect to intended load centers. This manual switch transfer can be installed fast and easily because each of its wires is marked.

Standard Switches: These switches can handle a higher current load of about 100 to 900 amperes. Although this type of manual transfer switch is fast and efficient, they are not economical.

Single Circuit Switches: As suggested by the name, these power single circuits. Because they cater to one circuit at a time, they are safe and easy to use and still economical. Single circuit switches are often used for furnaces and pumps.

Available Options for Manual Switches

Other than the different types, there are different options you can go for when it comes to manual transfer switches. These include;

Pre-wired case: This is the best option for you if you are looking for the easiest manual switch transfer to install and implement.

It is also a suitable option as it is safe and ensures easy swapping between power sources.

This option comes with a pre-built breaker box that provides all the necessary wiring needed.  All that is required is connecting the wires within it and attaching it to the backup generator.

Inlet Box: This option is set the same way as the pre-wired case. However, the main wire that connects to the generator is accommodated outside the establishment to prevent mesh.

Outdoor: This option is often used in areas that receive heavy rainfall all year through. This is because outdoor manual transfer switches have a waterproof housing that prevents seepage of water or moisture.

As suggested by the name, outdoor switches are installed outside the house or building to prevent damage near the main power source.

2. Automatic Transfer Switches (ATS)

This type of transfer switch operates in the same manner as the manual type. The only difference is the process is automated and doesn’t require manual manipulation of the switch.

An ATS acts as the brain connecting your building or home to the main power source and the generator.

During a power outage, the ATS will automatically switch the backup power source so it continues to provide an uninterrupted power supply.

Once the utility power is back, the ATS will automatically detect this, switch off the generator and switch back to the main power source.

Because an ATS is automated, they are more convenient than manual transfer switches.

ATS is also more efficient than their manual counterparts as they do not allow a definitive break or power loss.

An ATS can also handle more electric current than manual transfer switches.

Because ATS’s provide safety, power reliability, and simplified operations, they are suitable for homes and buildings with high power requirements.

An ATS is also a good fit for settings such as hospitals and industries, as they stand to suffer severe and even fatal losses in the event of a power outage or a definite power break.

Types of Automatic Transfer Switches

Automatic Transfer Switches (ATS)

There are four types of ATS’s based on the building’s electrical and power needs.

These include; open transition ATS, closed transition ATS, soft loading transfer switch, and bypass isolation ATS.

You should note that all these types of ATS have the same goal of automatically transferring power from the utility source to the backup source.

The only difference between the four types of ATS’s is that they’re all designed to meet different criteria and applications.

For this reason, you need a professional electrician to determine the type of ATS you need to cater to specific power needs.

Open Transition ATS: This type of ATS uses a system called break-before-make. This means that the transfer switch breaks contact with the previous power source before establishing contact with the other power source.

As a result, you should expect there to be a brief power supply interruption. This, however, lasts only a few seconds before a stable power connection is established. This break is necessary as it ensures the safety of utility workers.

An open transition ATS can only be used in settings where the brief power supply interruption will not cause extensive damage.

Open transition ATS is the most widely used type of ATS due to its reliability and simplicity in its processes.

A variation of the open transition ATS is the Programmed Transition Switch. This ATS pauses between the main source and backup source power, allowing the decay of residual voltage in circuits before restoring power.

Closed Transition ATS: This is also referred to as the standard or fast closed transition. The closed transition ATS can be used for settings that cannot tolerate even the slightest loss of power.

Such settings include hospitals, data centers, and large-scale businesses and industries.

 This type of ATS works on the same principles as the open transition ATS.

The only difference between these two types of ATS systems is that the closed transition system allows both power sources to be on simultaneously without the risk of overlap or backfeeding.

This state having both power sources on simultaneously is maintained for roughly a tenth of a second to establish a safe connection and prevent power loss.

Soft loading Transfer Switch: This type of ATS is the same as a closed transition ATS. However, the soft loading transfer switch is designed to adjust the power load it handles depending on the situation.

The soft transfer switch effectively controls the backup power speed and voltage to phase match that of the utility power source.

The soft loading transfer switch also allows the gentle transfer of load between any two power sources.

Due to this characteristic, soft loading transfer switches allow households and businesses to experience flexibility over more situations that need backup power. Soft loading transfer switches are, however, more costly.

Bypass Isolation ATS: This is the most complicated but most highly effective ATS system. It is designed to have two power sources running parallel to each other.

This system also allows the simultaneous inspection, testing, and maintenance of the two sources.

Due to its complex nature, the bypass isolation ATS can be used in the most sensitive and priority 1 environments such as telecommunication centers, air traffic control stations, and life support units.

Here is a video on the differences between manual and automatic transfer switches.

Safety Precaution & Importance of Professional Installation

Please note that wiring of transfer switches and installation of generators required to be done by professionally licensed electricians.

You should, therefore, not be tempted to take this on as a DIY project even if you have basic knowledge in technical and home electrical systems.

The National Electrical Code expects transfer switches to meet particular standards. For this reason, the following cautionary measure should be taken;

  • Install a monitoring device such as a wattmeter. This will help you to understand your power consumption and know when the limit is exceeded.
  • Always consider wattage when using any type of transfer switch. You can achieve this by ensuring the cord ratings match those of the utility or backup source.
  • Do not overload the generator. Ensure the generator only supplies power as per its load capacity. Only high-power generators (such as predator 3500 generator) should be used to power several circuits simultaneously.
  • Have your generator transfer switches installed by professional electricians who will maintain high safety standards. Professional electricians can properly size transfer switches so they match the power capacity of your backup power unit. This is necessary as it prevents power overload when the utility power comes back.

Remember, when looking for a transfer switch for your generator, always consider; the type of transfer switch you want, the wattage rating, comprehensive kits, UL/CUL certification, and warranty.

The Importance of a Generator Transfer Switch for Portable Generators

As mentioned before, a transfer switch isn’t considered to be a piece of necessary additional equipment when working with portable generators.

You are, however, advised to use a transfer switch even if you have a portable generator for the following reasons;

1. It’s a requirement from the National Electric Code: According to NEC article 700.5 and 701.5, every home using a portable generator is required to have a functional transfer switch professionally installed.  

This is especially helpful if you plan to sell your house in the future. Not adhering to this installation requirement is a violation for which you will be fined.

NEC® Requirements for Generators

2. It’s safer to connect a portable generator to your home using a transfer switch: Although you can use extension cords to connect your generator to your utility power grid, it creates the possibility of back feeding.

This could result in dangerous outcomes such as electrocution, serious injuries, death, or electrical fires.

NEC® Requirements for Generators

3. It’s more convenient to backup power during an outage with transfer switches than without: Having a transfer switch saves you the time and energy required to manually connect your portable generator to your house every time there is a power outage.

Instead of having to look for the extension cords, untangle them and switch on the power backup, transfer switches offer an easy, fast and reliable solution to this.

Sizing a Generator Transfer Switch

You need to determine the size or amperage of the transfer switch you need before making the purchase.

Amperage refers to the amount of electric current the transfer switch can accurately and safely handle.

Different transfer switches can accommodate the different amounts of electric current and this will be recorded on them as the amperage (amp) rating.

For example, a transfer that can handle 120 amperages will be given a rating of 120 amps. The difference in amperage is due to the different power needs one has.

These electrical needs have to be properly sized with the transfer switch and the generator as well to prevent poor performance or lack of performance at all.

One of the easiest ways to correctly size your generator’s transfer switch is by matching it to your generator’s load. To achieve this, you should match the transfer switch to the largest outlet on your generator.

Therefore, if your generator’s largest load is 25 amps, then you should match this with a transfer switch rated 25 amps.

This method of sizing a transfer switch is the easiest and only works when a professional has already sized your generator to your home’s electrical needs.

A more complex way of sizing your transfer switch is by determining what you intend to power with your generator.

This can prove to be difficult for anyone lacking the proper knowledge and should only be done by a professional electrician.

Even after accurately sizing the transfer switch and having it installed by a certified professional, you must avoid overloading the system.

Overloading the system can damage the generator and your electrical appliances. This is often due to supply too much power at once.

You can effectively monitor the system and prevent an overload through a wattage meter.

Generator Wire Size

  • 15-amp breaker: 14-gauge wire
  • 20-amp breaker: 12-gauge wire
  • 30-amp breaker: 10-gauge wire
  • 50-amp breaker: 6-gauge wire
  • 60-amp breaker: 6-gauge wire

Wire Size For Main Panel To Transfer Switch Wiring

  • 20-amp breaker: 12-gauge wire
  • 30-amp breaker: 10-gauge wire
  • 50-amp breaker: 6-gauge wire
  • 60-amp breaker: 6-gauge wire
  • 100-amp breaker: 2-gauge wire

Choosing the Right Generator Transfer Switch

There are other factors you have decided whether you need an ATS or an MTS, and you have accurately sized your transfer switch with your generator.

One of these factors is whether the transfer switch will be a single-circuit, dual-circuit, or multi-circuit.

High powered generator, often used in settings with high power demands, requires a multi-circuit transfer switch.

A low-powered generator, often used in settings with low power demands, will require either a single or double circuit.

You should also consider whether you want the transfer switch to be installed inside or outside the building or home.

Outdoor transfer switches have a NEMA 3R designation and can withstand severe weather conditions without being damaged.

You also need to consider how the transfer switch works, the continuous current rating, and the load type.

How the transfer switch works refers to its design. For an ATS, this refers to whether it is an open transition, closed transition, soft loading, or a bypass isolation switch.

For an MTS, design refers to whether it is a simple KITS, specified circuitry, rated load centers, single circuit, or a standard switch.

You should only consider the continuous current rating if you intend to purchase an ATS. The ATS you choose should be able to supply backup power for up to 3 hours or more.

Current ratings of automatic transfer switches often range from 30 to 400 amps and should match that on the main breaker.

There are three types of load types; total system loads, restrictive loads meter and electric discharge lamp and incandescent lamp loads.

Generators are often marked with the load type they handle. As such all, you need to do is match the generator’s load type with that on the transfer switch.

You should also note it is often recommended to pair ATS’s with generators with a total system load.

Installing and Using a Transfer Switch

Before installing the transfer switch, you should make sure you have the following; a generator, an individual transfer switch, a power inlet box, and a generator power box.

You must remember that transfer switches should only be installed by a professional electrician.

Even so, we will offer you a checklist of essential steps that should be followed when installing a transfer switch:

  1. Find the appropriate location to mount the transfer switch.
  2. Switch off the main power.
  3. Establish which household circuits are a high priority.
  4. Locate and connect wires coming from the transfer switch to the circuits in the panel box.
  5. Connect the electrical cable from the transfer switch to the electrical box and connect the electrical receptacle.
  6. Make sure your generator is in good condition.
  7. Start the generator and flip the transfer switch.

Conclusion

From the guide above, you should have an idea what a transfer switch is all about. This is important so that you can always buy the right transfer switch depending on the applications.

You can always enlist the services of a professional to help you further on the choice of a transfer switch. The same applies to the installation part too.