Using an extension cord with a portable generator is fairly straightforward. Different generators have different outlet configurations, and you'll need a cord with the correct plug for your generator. At the other end, you'll have outlets that can connect with the devices that you want to run, or with a power inlet attached to a generator transfer switch, if you have one installed. If you plan to use your generator for backup power during an emergency, the extension cord needs to be long enough to allow the generator to be at least 20 feet from the house. The cord should have an amperage rating that can accommodate the amperage rating of the generator's outlet (typically 30 amps, but check with the manual or manufacturer of your unit). The amperage rating of the cord should also be sufficient for the devices you plan to power with it. Special generator extension cords are available.