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Connecting A Portable Generator To Your Home

July 28, 2006

Q: I need a 25ft. 220v extension cord for my generator. Outlet on generator is 120/240v, four plug adaptor? Opposite end will be a dryer type plug. Need to know what type of plugs and wire to purchase, and where to purchase, so I am able to make the cord.

A: You CANNOT do this. It sounds to me like you are going to backfeed into your dryer receptacle to provide limited power to your home during an emergency. This is illegal, unsafe and will end up killing someone.

This is a National Electrical Code (NEC) violation. NEC article 406.6(B) states “Connection of Attachment Plugs. Attachment plugs shall be installed so that their prongs, blades or pins are not energized unless inserted into an energized receptacle. No receptacle shall be installed so as to require the insertion of an energized attachment plug as its source of supply.”

This is unsafe because the dryer type plug end of the cord that you want to make will have live prongs or blades with either 20 or 30 amps at 240 volts. This will easily electrocute and kill someone. 

You need to install some type of transfer switch so power can’t backfeed into the utility lines and kill the utility personal trying to repair your electricity.

I would install either an automatic or a manual transfer switch with a flanged inlet locking receptacle under or in the transfer switch. Some transfer switches come with this built-in. The manual transfer switch is approximately $200.00 verses an automatic transfer switch at approximately $400.00. Now, you can make an extension cord to feed this receptacle and have a safe and legal installation.

You need to look at the receptacle on your generator to determine what it is. This is probably either a 20 or 30 amp twist-loc receptacle. The receptacle should have a NEMA configuration number on it. If it is a 5,000 watt generator it is probably a 20 amp receptacle and the number will be L14-20R. For this application you need a L14-20P locking plug (Leviton catalog #2411) with #12 AWG SJ cord and L14-20R locking connector (Leviton catalog #2413). The flanged inlet locking receptacle is a Leviton catalog #2415.

If it is a 7,500 watt generator it is probably a 30 amp receptacle and the number will be L14-30R. For this application you need a L14-30P locking plug (Leviton catalog #2711) with #10 AWG SJ cord and L14-30R locking connector (Leviton catalog #2713). The flanged inlet locking receptacle is a Leviton catalog #2715.

Don’t forget to ground your generator’s frame. The first system I set up for myself like this, I installed an 8′ x 5/8″ galvanized ground rod in the ground where my generator was going to sit during an outage. I left the coil of #6 bare copper wire connected to the lug on the generator’s frame and the acorn clamp on the ground rod. When we had an outage, I would roll up the generator, connect the ground wire and start the generator. Then I would connect my cord from the generator to the transfer switch and change the transfer switch from utility power to generator power and I was up and running again.

After doing this a few times, I elected to get one of Generac’s generators with the automatic transfer switch. I really like this because when the power goes out, within 1 minute my generator is running and power has been automatically transfered.

Here is a website where you can get everything that you need. I have never used these guys before, but the have exactly what you need. http://www.nbmc.com/emergen/


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6 Responses to “Connecting A Portable Generator To Your Home”

  1. Gene Wade on July 7th, 2008 6:32 pm

    Would appreciate step by step instructions on how to connect a 5500 Watt generator to a 100 amp manual transfer switch.

  2. TrepasseyWindPower on October 16th, 2008 10:45 am

    If you are not connected to the grid, how can this impact anyone but the home owner? Too many people think that the utility owns the wires inside the home. If you are off-grid you have the freedom to connect anyway you see safe and fit.

  3. buickanddeere on December 10th, 2008 7:32 am

    Around here all structures no matter connected to the grid or not. The wiring must meet code requirements according to the law. Plus insurance companies will NOT payout if the wiring system is not inspected and approved.

  4. Chris defeo on April 16th, 2010 12:33 pm

    I am connecting a generator through a transfer switch to my panel box. The generator is 5500 watts, 30 amps, 240 volts. It is about 70 feet away (bends,turns, etc in the house). What size wire should I use? I also want to plan for the future if I get a bigger generator (40 amp, 8500 watts)

  5. Bill Powers on September 4th, 2011 5:07 pm

    You might want to suggest interlock kits from http://www.interlockkit.com as a safe and easy solution to connecting generators to home panels. My electircal company gets about $700 to install these and we can do it in about 2 hours. Inspectors love it and it is much easier than transfer switches. Just thought I would pass it on.

  6. Keith Arthur on January 15th, 2012 3:00 pm

    Just a quick question about procedure for hooking up a generator. You mentioned that when you had a manual transfer switch, you started the generator before plugging it into the transfer switch. Seems to me that you’d want to plug the generator in first and then turn it on so that you don’t have a cord with 30 or more amps in your hands. I’m new to this, so that’s why I’m asking.