How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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Why did my generator hookup get tagged as defective by the home inspector?
Thursday, October 18, 2018
There are several different ways to properly connect a generator to a house electrical panel for use during a power outage. All of them have one thing in common: they are configured in way that makes it impossible to have both the generator connection and the electric utility connection to the panel switched on at the same time.
We sometimes find a breaker in an electrical panel marked “generator” and connected to a nearby wall receptacle configured to accept a connection cord to a portable generator. An example is shown below. This is called “backfeeding” the panel. In a power outage, one of the breakers that would ordinarily be wired to feed electricity out to receptacles or appliances around the home is, instead, wired to backfeed electricity into the panel bus bars for distribution out through the other breakers out to the home.
While backfeeding a panel in itself is not unsafe, it becomes unsafe when there is no foolproof safety device to lock-out the electric utility service when the panel is being backfed by a generator. Sometimes we see printed instructions posted on the panel to first turn off the main breaker before turning on the generator breaker.
But printed directions are not sufficient. Connecting a generator directly to the electrical system of a building in this manner has the potential to feed through the building’s electrical system to the outside utility service lines, and can kill or injure a person repairing service lines if the instructions are overlooked--which is easy to do in the clamor and confusion after a major storm event.
Also, if your electric utility’s line crew restores electrical service while the generator is connected to the incoming utility service, you could start a fire or seriously damage the building. Manufacturers of the generator plugs even mark them with a warning sticker like the one below.
One safe solution to this problem is shown in the photo at the top of the page. The metal plate slides up-and-down between the lower breaker (main electric service breaker) and the upper breaker (backfed generator breaker) in a way that makes it mechanically impossible to have both breakers in the “ON” position at the same time.
Another solution is a separate subpanel that feeds only selected circuits in the home, with a double-pole double-throw transfer switch to connect the generator panel to the building’s electrical system. Connections must also meet the local ordinances and building codes. A minimum of #10 AWG wire is typically required. An example of one is shown below.
And a third solution is an automatic transfer switch, like the one shown below, that are installed with larger, permanently-mounted generators providing 12,000 watts or more of power.
The most important thing is to have a qualified, licensed electrician do your generator connection system installation. They will know the right way to do it to keep you and your family safe in the aftermath of a storm or other power outage event.
Also, see our blog post What is the best emergency back-up generator for the power outage after a storm?
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