Everything You Should Know About Generator Interlock Systems

Everything You Should Know About Generator Interlock Systems

Texans learned a hard lesson during the winter of 2020-2021: yes, the polar vortex can happen here, and the electric power grid can be down for days, or even weeks. After a winter like that, it’s a fair bet that a high percentage of Texans who didn’t own a generator hustled right out to buy one.

But there’s a lot more to preparing to use a generator to keep the lights on when the power goes out than you might think. That’s why we’ve created this brief guide to >everything you should know about generator interlock systems.

Safety First

First on the list of everything you should know about generator interlock systems is that a generator interlock system is a safety device. It prevents the main electrical circuit and the circuit dedicated to receiving power from a generator from being on at the same time.

Why is that important? Because of something called “backfeed”: when you use a generator, you are “backfeeding” electricity from the generator into your circuit panel. But if the main electric breaker is on at the same time a generator is feeding power to your circuit board, you can generate backfeed to the power lines out in the street.

If there’s a power outage, or any other time workers are servicing electric lines, workers believe the lines they’re working on are not live. But if the lines are carrying power that is backfeeding from a residence, those workers won’t know it, and they could be electrocuted. That’s why backfeeding is illegal.

Another safety concern is that portable generators are powered by gasoline or propane, and they emit an astonishing amount of potentially deadly carbon monoxide gas. According to a video from the National Institute of Standards and Technology (NIST) posted on the Center for Disease Control’s information page about carbon monoxide poisoning, a portable generator can put out as much as 100 times the carbon monoxide as a car’s exhaust.

It’s a no-brainer that portable generators should NEVER be used indoors or in any enclosed space, like a garage or shed. People have become sick or died from carbon monoxide poisoning when using gas-powered tools in very large, enclosed spaces, even with windows and doors open and fans on.

So your generator will be running outdoors, as far away from your house and your neighbors’ houses as you can place it. The generator’s exhaust should face away from your house, and it shouldn’t be anywhere near windows, vents, or ducts on your house or your neighbors’ homes.

The NIST study in the video referred to above found that 15 feet wasn’t far enough away to prevent the risk of carbon monoxide entering a home. Unfortunately, the study failed to establish a minimum safe distance, so “more than 15 feet, as far away as possible” is the best rule of thumb we’ve got.

Is Your House Ready for a Generator?

Now that you know the risks of running a portable generator in enclosed spaces, too close to your house, or backfeeding electricity, potentially killing power company workers, it’s time to check to see if your house is ready for a generator.

In order to get electric power from your generator into your home and direct it to the correct circuits to get the lights back on and the refrigerator working, you’ll need:

  • A dedicated external power inlet: a professional, licensed electriciancan install a special, waterproof power “inlet” on the same side of your house where your generator will be placed outdoors. This will allow you to connect the power from the generator to a dedicated circuit inside your house.
  • A generator extension cord: you’ll need a generator extension cord rated for the wattage your generator can produce, that matches the inlet your electrician installed, and that connects correctly to the outlet plug on the generator itself.
  • A generator breaker: if your electrical panel doesn’t already have an extra breaker that can be wired to the external generator inlet, you’ll need to have your electrician install one. Having a clearly marked breaker specifically devoted to your generator is critical to safely sending power from your generator into your house.
  • A generator interlock: the generator interlock is a small plate that is attached to the front of your electric panel. It covers up the generator breaker so it CANNOT be turned on when the main electric circuit is on.

There are many different styles of electric panels, and the interlock must match the design within your circuit box, so it fits correctly to block the dedicated generator breaker. It should also slide up to block the main switch when you turn the main off, so you can’t turn it back on when you’re running your generator.

If your home doesn’t have a breaker for the main electrical supply, your electrician must install one. This is so you can turn the main circuit off to prevent backfeed when you use your portable generator.

How Does an Interlock System Work

An interlock plate attaches to the front of your electric circuit panel with screws. To install it properly, the front of the panel must be carefully removed and marked accurately so that the plate of the interlock will fit correctly.

Once the interlock panel is attached and the panel is replaced over the circuit breakers so they fit in the correct openings, the interlock can be positioned as needed. If nothing is wrong with your power and you won’t be using your generator, the generator breaker should be off and the interlock should be blocking it, so you can’t turn it on.

In the event of a power outage, you’ll retrieve your portable generator from storage, get it set up outside with the generator extension cord, and turn it on to warm up.

Then, you’ll come back inside and use a flashlight to locate the main breaker, and TURN IT OFF. Turn off all unnecessary breakers, so you won’t overload your generator when power is flowing from it into the house.

Once the main is off, you can slide the interlock up, unblocking the generator breaker, so you can turn it on. The interlock is now blocking the main breaker, so you can’t turn it back on while your generator is running and the generator breaker is in the on position. Your generator is now backfeeding your electric panel and the circuits you’ve elected to leave on.

You may have to turn on a battery-powered radio to find out when the power is restored to your neighborhood. When it is, you simply reverse the process, turning the generator breaker off and sliding the interlock down, so you can turn the main back on.

Allgood Electric provides the home electrical services you need, including generator interlock installation services in San Antonio.

Everything You Should Know About Generator Interlock Systems
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