I am planning on installing an interlock kit and backfeeding my panel with my portable generator. The backfeed will be to a 30 amp breaker, coming from the 240/30A outlet on my Generac 5500. The question is about the distance the generator can be from the panel.

I can install the outdoor inlet right outside wall with the panel, resulting in around a 6 foot run of 10-3 romex with ground. However, while the generator fine there, it would be little harder to get to in that location for refueling and maint.

Alternatively, the most convenient spot for the generator would result in about a 80 foot run of 10/3 romex. Will that length of run affect the performance or reliability of the power?

1 Answer 1


As has been discussed many times in this forum, back feeding a generator into a double or even a single pole breaker without a transfer switch is risky business. If the main breaker is not disabled while generator is online, you will be back feeding power to the grid and pose a safety hazard to utility workers.

With that said, look at the following link, http://www.southwire.com/support/voltage-drop-calculator.htm The wire size for an 80 run at 30 amps/120vac is 8 AWG. Use this calculator to determine wire size or determine voltage drop. 3% drop is usually considered max for 120/240 runs. Once you start to draw amperage, the drop can become greater as you tax the voltage source with a fixed or max amp output.

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    The question states that he is using an interlock. Which would prevent backfeeding if installed correctly. Commented Jan 7, 2013 at 13:00
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    backfeeding the grid is not the only concern here. While using an iterlock, it's possible (and usually quite easy) to overload you generator (unless the gen is sized to power your whole house).
    – Tester101
    Commented Jan 7, 2013 at 13:18
  • @Tester: totally agree. A severe voltage drop can damage appliances, motors, electronics. Risky business if not sized properly. Commented Jan 7, 2013 at 14:16

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