Transfer Switch Equipment 101

In many cases, blackouts are nothing more than minor annoyances.  However, there are also times when a blackout can last for days and cause serious problems for both homeowners and business owners.  For this reason, many are investing in backup generators that will deliver electricity to where it is needed most.

Transfer switch equipment is a key component of all backup generator systems and these come in many types.  In addition to the type of power transfer equipment, it is important to consider whether manual or automatic transfer switches are best for your specific application.  Here are the main classifications, and their pros and cons, which may help you make a decision:

Types of Transfer Switch Equipment

Transfer switches can be categorized into four main groups:

Open-transition transfer devices:  Also called a “break-before-make” transfer switch, this type opens the source of power before severing the connection to the second source and has a small period of downtime as a result.  They are the most commonly used type of transfer switch and can be used in various applications.

Fast closed-transition transfer devices:  These devices operate in a similar fashion to open-transition transfers, but they will parallel the two power sources momentarily, and then break the connection when both sources become available.  They perform a “make-before-break” transfer switching action, and total interruption is avoided.

Soft closed-transition transfer devices:  These devices also operate like an open-transition transfer switch when a power outage occurs, except they will synchronize the sources during transfer.  In this device, minimum interruption to the loads occurs.

Sub-cycle transfer devices:  Sub-cycle transfer devices open and close the new source so quickly that most load devices aren’t even affected by the interruption.  These devices tend to be more expensive compared to other mechanical switches and are commonly protected by fuses.

Automatic Transfer Switches

Automatic transfer switches are used in permanently installed standby generators and automatically switch from utility power to backup power in the event of a power outage.  When the power is restored, it automatically reverses the process.  They can come in an array of sizes and styles.  Sizes of automatic transfer switches can range from 50-amps to 400-amps, while styles range from standard and load centers, to service disconnects.

Advantages

Automatic transfer switches do not have to be actuated by anyone in order to run—something that is extremely helpful for those who don’t want to stumble around in the dark to find the service entrance panel.  Another advantage of automatic transfer switches is that they usually provide operators with many different control and alarm features that are extremely useful.  Some automatic transfer switch equipment can even start and stop the generator according to a schedule that the operator sets.

Disadvantages

While automatic transfer switches are convenient when no one is around to operate the generator, they do come at a steeper price.  This deters many from investing in automatic transfer switches.  They also can’t be used with portable generators unless the generator has an electric starter.  Due to their complexity, only experienced electrical contractors should install them.

Manual Transfer Switches

Manual transfer switches must be turned on and off by hand and can be seen in both portable and stationary generators.  Usually a single power cord will connect the backup generator to the main power supply.  In some installations, it is more practical to select a manual transfer switch because the load is not critical and because operating personnel are on hand to attend the operation.  Typically used for home usage and low-power situations, manual transfer switches are particularly useful for portable generators.

Advantages

One advantage of a manual transfer switch is that it tends to cost much less to design and install, compared to an automatic transfer switch.  They are also not as complex as automatic transfer switches, but it is still strongly recommended that electrical contractors handle the installation.

Disadvantages

If the operator did not note the loads on their branch circuits before the power went out, it isn’t uncommon for the generator’s capacity to be overloaded.  However, many new models of transfer switches now have selective load transfer switches that can provide an alternate source of power to specific branch circuits that were selected in advance by the operator.

Which Transfer Switch Is Right for You?

Power outages can cost businesses a lot of money, and it is important that the best transfer switch equipment is chosen.  The various types of transfer switch equipment all have their advantages and disadvantages, and taking your specific application into account will depend on which type you choose.

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