What is Transfer Switch : Working & Its Applications

Generally, hospitals, buildings, data centers, and other institutions and commercial complexes typically use an emergency power source like an electric generator otherwise backup utility feed whenever power failure occurs. To overcome this, a transfer switch is used for safely and quickly changing all electrical power utilized by the systems or equipment connected to the output of this switch between two power sources like normal and emergency. This article discusses an overview of a transfer switch – working with applications.

What is Transfer Switch?

A transfer switch can be defined as, a switch that is used to allow the secure connection or disconnection of various electricity sources toward an electric load. Generally in homes or offices, a generator is used to provide backup power. So transfer switch is connected where a generator is arranged so that the generator may give temporary electrical power if the power failure occurs. These switches are used to switch between a generator & grid service; between various generators; or various grid service entrances.

How Does a Transfer Switch Work?

The transfer switch working principle mainly depends on a fast switch between the energy sources. So these switches are helpful in switching electrical energy among two power sources quickly & securely like primary & backup power sources. This switch is an intelligent and self-acting power switching device. The function of this switch is to ensure constant electrical power delivery to a connected load circuit from one of two power sources. Here loads are motors, lights, computers, etc.

The transfer switch detects the power off condition by the load current and voltage drop. The load is a motor, furnace blower or any other device that draws a large amount of current. When an interruption occurs, the motor will stall as there is no longer any voltage or current flowing to it. The motor will draw an inrush current as it attempts to restart; this surge must be restricted to prevent damage to the motor.

The transfer switch senses the inrush current by measuring the voltage across one side of the load while measuring the current through it. If there is no power to the load then there will be no voltage across it and there will be no current flowing through it either. In this case, when power returns then there will again be an inrush surge in current which must be limited by turning on relays within the transfer switch before allowing full voltage back into your home.

Transfer Switch Types

There are different types of transfer switches available in the market which include the following.


Manual Transfer Switches

The transfer switch which operates manually is known as a manual transfer switch. These switches transfer load between two power sources like utility & backup power sources. This switch simply connects the electrical circuits of the house to the generator. Throughout a power failure, this switch can be used on the backup power. When any load is connected to the electrical circuit that will work on backup power till electricity is restored. This switch can be connected both indoors & outdoors.

Manual Transfer Switch
Manual Transfer Switch

Manual switches are very simple, and cheaper as compared to automated switches. These types of switches are banned in come safety-critical applications wherever it is required to rapidly switch power sources whether a person is there or not.

Automatic Transfer Switches

The transfer switch which operates automatically is known as an automatic transfer switch or ATS. This switch is used to transfer the power supply automatically from its main source to a backup source once it detects a power outage in the main source. When a power outage takes place within a primary power system, then this switch invokes an uninterruptable power supply.

Automatic Transfer Switch
Automatic Transfer Switch

Since the ATS is connected to both power sources, then it works like a mediator in between the power supplies & equipment, performing like an electrical relay. The vendors of ATS mainly include Dell, APC, Cummins Power Generation, Western Telematic & General Electric.

Transfer Switch Wiring Diagram

Generally, hospitals, data centers, factories & wide range of institutional and commercial applications normally need an emergency power source like a backup utility feed or generator when the normal power source is not available. So, a Transfer switch is responsible for securely & rapidly changing all electrical power used by the circuits, systems, or equipment. So these are simply connected to the output of transfer switch between those emergency & normal power sources.

Here, electrical energy which is used by the system, circuit, or equipment connected to this switch output is called the load. The transfer switch wiring diagram is shown below. A typical transfer series mainly includes the following steps.

Transfer Switch Wiring Diagram
Transfer Switch Wiring Diagram

When the normal power source is not available or fails. Once the generator powersand if  the backup utility feed is constant & in fixed voltage and frequency tolerances, then the transfer switch moves the electrical load toward the emergency power source. So based on the required facilities & preferences, the energy transfer occurs either manually or automatically.

Whenever utility power is restored, then this switch returns the load from the emergency power source to the normal one. Once more, this can occur manually or automatically based on the type of switch being utilized & its mode of operation.

How to install a transfer switch ?

Installing a transfer switch is not difficult if you follow the proper procedures and take proper safety precautions. The following steps will guide you through the process:

1) Determine how many circuits are required for your installation. First, determine how many circuits will be powered by the generator. Each circuit should have its own individual breaker or fuse. For example, if you plan on having three circuits connected to your generator, which include one circuit for lights and two circuits for appliances such as a refrigerator and furnace blower motor, you will need three breakers or fuses installed in the panel box of your home.

2) Make sure there is adequate space in your panel box for installing additional breakers or fuses as well as plugging in extension cords from the generator. If there is not enough room for installing all of these items, consider installing an additional breaker box outside of your house where an extension cord can be plugged into it. You may want to consult with a licensed electrician before doing this step.

How do I use a transfer switch ?

You can use a transfer switch in any number of ways-  It allows you to choose where power flows within your home. For example, If you have an emergency generator, you can use transfer switch to automatically turn on certain lights when it kicks in during a power outage or if there’s an outage in your neighbourhood , you can use a transfer switch to help prevent damage by isolating certain appliances from the grid until power returns.

Advantages and Disadvantages

The advantages of a transfer switch include the following.

  • Automatic transfer switches (ATS) are required for uninterrupted electrical supply.
  • This switch is perfect for switching efficiently to generator power.
  • It is perfect for low-accessible generators.
  • An ATS offers many advantages to your business like increased safety, simplicity, and reliability.
  • This switch can transfer the load of the power automatically onto the generator. So this makes the change from the major power supply to the generator.
  • ATS includes inbuilt sensors for detecting fluctuations within the frequency & voltage of the power supply.
  • These switches have a time delay mechanism, which protects both the generator & your circuits from the fluctuations within power.

The disadvantages of transfer switch include the following.

  • The automatic transfer switch responds to false signals occasionally.
  • As compared to a manually operated switch, its cost is high.
  • This switch requires more maintenance as compared to the manual model.


The applications of transfer switch include the following.

  • Transfer switches avoid the flow of electricity in the wrong direction like from a generator in the home to the power grid.
  • These types of switches are used in CBs or circuit breakers to ensure the safety of your home appliances.
  • This switch plays a key role in protecting both utility & generator supply.
  • These switches are used for operating low power generators in homes and otherwise small industries.
  • The ATS transfers electrical power between two power sources a primary utility source & backup power source. These switches are also used in other electricity switching applications like utility to utility, the generator to generator & three-source systems.
  • This switch is very helpful in switching a load in between two power sources.
  • This switch allows you to utilize the wiring system of your home to control any appliance in your home by using a generator easily & quickly.
  • These switches allow loads to connect to backup & utility power sources.

Thus, this is all about an overview of a transfer switch – types, working with applications. These switches simply support several operation modes as well as transition types, and they have a different range of switching mechanisms. These switches have the capacity to control & switch between the two power sources in less time when a power failure occurs. Here is a question for you, what is an alternate name for the transfer switch?