Automatic Transfer Switch vs. Interlock: Which is Best?

A  standby or backup generator can be a lifesaver when the power goes out. As a storm rages, the generator starts up and restores lights, ventilation, computers, devices and other critical systems.

But how will electricity transfer from utility power to backup power in the event of a blackout? Depending on your power needs and application demands, you might require an  automatic transfer switch or an interlock. The type of switch you choose determines what happens when the power goes out.

Each device determines how the power flows from the  generator into your building. You must have an approved switch installed according to electrical codes to use a generator safely. Both types of switches prevent dangerous conditions that could harm electrical workers and potentially damage the building as well as any electrical devices.

Is an automatic transfer switch or an interlock best for you? Read more to find out which is right for your backup power application.

• What's an Interlock?
• What's an Automatic Transfer Switch
• Automatic Transfer Switch vs. Interlock: Which is Best for My Application?
• Get Help from the Experts at General Power

What’s an Interlock?

An interlock is a device that manages the power source to the electrical panel. The interlock ensures that the generator circuit breaker and the main circuit breaker cannot be turned on at the same time. The interlock guarantees the safety of anyone working on the electrical lines and prevents dangerous electrical feedback in the building.

How an Interlock Works

An interlock is manually operated. In residential or light commercial use, the interlock switch is moved from the main power breaker to the generator breaker when the utility power goes out. The main breaker and all other breakers must be turned off, the interlock switch is set to generator, and then the generator is engaged. The main breaker is turned on to energize the panel, and then individual breakers are turned on as needed.

What’s an Automatic Transfer Switch?

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An automatic transfer switch or a transfer panel is a device that senses and automatically switches between power sources. An automatic transfer switch automatically starts the generator when the power goes out or becomes unstable and then switches back to main utility when utility power is restored and normal conditions are met.

How an Automatic Transfer Switch Works

When a loss of power is detected, an automatic transfer switch works with your generator or auxiliary power source to start when your primary source of power fails. Sophisticated transfer switches can be controlled and monitored remotely.

Like an interlock, an automatic transfer switch ensures that the main power and generator power are not feeding the panel at the same time.

Automatic Transfer Switch vs. Interlock: Which Is Best for My Application?

There are a number of factors that go into deciding which is best for your application. You'll want to consider  generator size, electrical load, availability of on-site operators, frequency and duration of outages, and the demands of building occupants, among other things to find the right solution. Cost is also a factor, but safety and ease of operation will be worth more during an emergency.

When to Use an Interlock

Interlock switches are usually less sophisticated and therefore less expensive than automatic transfer switches. They require training and an understanding of the building's electrical system for safe use.

Interlock switches are often used in residential and small commercial applications where continuous power is not required. They are simple to operate, but there may have to be additional power management to turn off breakers for circuits that exceed the generator's capacity. Someone with the proper training must be or come on-site to operate the interlock switch and engage generator power.

Interlocks are best for:

Contents:

• Residential or smaller commercial applications
• Applications that do not require continuous power
• Applications where someone is on-site and able to operate the interlock manually

When to Use an Automatic Transfer Switch

An automatic transfer switch is used in applications or situations where the power must come on automatically.

Most commercial buildings require some form of alternate power source for life safety purposes and to comply with the National Electrical Code and other building codes. For example, refrigerated food cases in grocery stores or critical life-saving equipment in hospitals may be connected to an automatic switch.

They are also common in residential applications in locations that experience frequent power outages due to storms.

Automatic transfer switches are best for:

• When the user prefers having a fully automatic system that requires no supervision
• Commercial or industrial applications
• Applications that require continuous power
• Applications where automatic power transfer is required

Get Help from the Experts at General Power

Consult with the experts at General Power to configure a generator set for your unique needs. We'll help you select the right alternator and generator accessories to fit your requirements. Contact our team to custom configure an industrial-grade generator set for your power needs, or call us at 1-888-819-5646.