When preparing for emergencies, anticipating the unexpected can go a long way — and that’s especially true for backup power systems. Generators are often relied upon as the first line of defense during power outages, interruptions, and blackouts caused by severe weather. But generators also need a mechanism that safely contains and prevents the power source from causing more critical issues, like electrical backfeeding.
Source: homeserve.com
Electrical backfeeding and how to prevent it
Electrical backfeeding happens when the electrical current flows backward from the residential generator connection, into an electrical panel, and out to the outside power line or transformer. This can be dangerous for utility workers trying to restore power by increasing the chance of electrocution.
Electrical backfeeding can also cause problems in other homes if the malfunctioning current manages to flow into nearby residential circuits or other transformers within the same grid. This scenario can cause fires, blow out panels, and completely damage the generator.
To prevent such devastation, it is advised to consider getting a generator transfer switch or a generator interlock kit. Below, we’ll talk through each option to help you decide which one is right for your application.
Source: support.generac.com
What is a transfer switch?
A transfer switch is a separate panel that works with the main electrical panel to help the generator power select circuits for essential appliances in the home during an emergency, such as kitchens, refrigerators, septic tanks, well pumps, living rooms, etc.
Transfer switches also have a specialized switch that allows users to pick between utility power and generator power, as it cannot be connected to both at the same time. While in generator power mode, the transfer switch will isolate the power source from the utility grid and transfer it to the installed generator. For a manual transfer switch, users need to wait until after the power has gone out or gone down to use this feature by hand.
But for an automatic transfer switch, also known as an ATS, the switch is automatically flipped from utility power to generator power as soon as the power goes out. When paired with a standby generator, users experience only a minor 10- to 30-second delay before backup power starts and voltage levels stabilize.
Source: support.generac.com
What is an interlock kit?
An interlock kit is a sliding piece of metal mounted on the main electrical panel’s connection to the generator power source or breaker. It then works together with an outdoor power inlet box where the generator plugs in, acting as a physical barrier to block the utility power source when the generator is turned on.
Unlike generator transfer switches, the interlock kit uses and energizes an existing electrical panel to allow for individual and manual selection and control of household circuits — directly from the main electrical panel.
In other words, the utility power source and the generator power source cannot be on at the same time. However, the user must take care not to overload a generator’s wattage limit. Failure to do so can cause the generator to trip and stall. Plus, interlock kits must be compliant and up to date with NEC standards, compatible with the specific panel and model it’s attached to, and permitted to be installed in the area based on local building codes.
Transfer switch vs. generator interlock at a glance
| Generator transfer switch | Generator interlock kit | |
| Average cost & price range | $500 – $1,500+ for manual transfer switch purchase, including installation costs (ATS can be much higher) | $50 – $150 purchase, not including installation cost which can range from $400-$800 |
| Operation & function | Limited access and power control; easy to manage with the flick of a switch | Full access and power control; requires constant management of a generator’s wattage limit to prevent stalling |
| Compatibility | Works best for small- to mid-sized generators at around 8,000 watts or less (ATS can handle much higher ranges) | Can work with generators of any size, but tends to work best for mid- to larger-sized generators |
Sources: consumerreports.org and How To Home
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Browse our collection of transfer switches and interlock kits for your next backup power installation project at City Electric Supply (CES) online or at a branch near you!