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1) Whenever backfeeding an electrical panel with a portable generator, you will either require a transfer switch or an Interlock kit to isolate the public utility grid from your generator during a power outage. The XFER switch or Interlock kit prevents utility linemen workers from getting injured or killed while they are working on utility lines during a power outage.
2) The easiest and most cost effective and recommended method is to install an Interlock kit at the main electrical panel. The Interlock will allow you to select which circuits that you want to be powered from the generator.
3) If the generator has a 30 amp/240 volt plug (most common), the main electrical panel will require a 30 amp double pole circuit breaker along with 2 spare circuit breaker spaces. The garage 240 volt receptacle will need to be converted to a power inlet box which must also be compatible with the generator receptacle NEMA rating.
4) You will also require the compatible cord that plugs from the generator to the 240 volt power inlet based on the gen set receptacle NEMA rating.
5) See link shown below for an Interlock kit:
6) The wall receptacle needs to be converted over to a power inlet. It is a code violation and a safety issue to use a male-to-male cord from the gen set to a wall receptacle. In the electrical industry, we refer to this as a "suicide cord". Suicide cords are never allowed.
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