What is a Transfer Switch?

A report by Climate Central found that power outages from extreme weather have spiked by 67%. These events have increased the need for backup power supplies. Emergency generators provide backup power to mission-critical facilities, businesses, and homes during power outages, keeping essential equipment such as life safety and critical systems up and running. To do so, backup power sources must be connected to the equipment it serves. That’s where transfer switches come in.

Definition

A Transfer Switch is a device that transfers electrical loads between power sources, such as utility power and generator power. During an outage, it is used to connect electrical loads to a backup power source, typically a generator. Depending on the transition mode selected, the transfer switch can do this without impacting downstream equipment, or by introducing a strategic delay. In addition, it prevents generators from back-feeding the power grid, thus supporting safety objectives.

Incorporating this device is a way to comply with electrical codes and standards. For example, the National Electric Code^® requires a permanent switching means for connecting a contingent power source for establishments with a single generator. When paired with a connection panel, this best practice allows for a reliable temporary generator for homes and businesses when power for an emergency load is needed, resulting in speedy connection and minimized downtime.

Where can transfer switches be applied?

The versatile device can be integrated into different settings. This includes but is not limited to the following uses.

• Data centers
• Commercial buildings
• Small businesses
• Hospitals
• Residences
• Water treatment plants
• Telecommunication facilities

How does it work?

Transfer switches are installed between a building’s power distribution system and its power sources. It is used to transfer a facility’s electrical load between the power sources to connect an active source of power. The device contains a mechanism that disconnects electrical load from one source and connects it to another.

Transfer Switches are not Circuit Breakers

Circuit breakers protect electrical circuits from overload by opening to interrupt power flow when overcurrents occur. On the other hand, transfer switches connect a power source to a circuit, even when overcurrents up to the device's’ maximum ratings occur.

Types of transfer switches
The three primary options for transfer switches are as follows.

Manual

Manual transfer switches remain connected to one power source until someone operates it to connect the alternate source. It requires a qualified individual to recognize an outage before operating the device to transfer loads from one power source to another. Manual transfer switches offer simple cost-effective solutions for applications that can tolerate momentary power interruptions.

Automatic

Automatic transfer switches offer unattended operation. They detect power failures, initiate generator startup, transfer load, and perform other functions without human intervention. They also return loads to the normal power source after power returns

Non-automatic
Non-Automatic Transfer Switches require a qualified person to operate it. However, it can be operated using local or remote controls. This enables someone to operate a transfer switch from a safer location. It also can make transfer switch operation simpler and more convenient than manual transfer.

Transfer Switches from ASCO Power Technologies

ASCO offers a wide array of transfer switches to suit business, mission-critical, and residential applications. Learn more about how transfer switches keep power flowing here.

Reference:
1. Power OFF: Extreme Weather and Power Outages. (2020, September 30). Climate Central.
https://medialibrary.climatecentral.org/resources/power-outages. Accessed September 2, 2021.