Portable generator cord length

sarahlee123October 12, 2011

I have a 5000 watt generator that I can plug into an outside outlet that is connected to a big transfer switch alongside the circuit break box. The connecting cord I have now is not long enough to keep the generator where I want it. How long a cord can I use - does extra length affect how the generator works? Any help would be gratefully appreciated.

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Yes, there is a limit to how long a cord you can use.

Basically, there's a voltage drop in any wire, depending on the length and the diameter of the wire. You want to limit that drop between the generator and the devices that use it (particularly motors) to about 5%. Realizing that there's the cord from your generator to your circuit breaker box, and then wires to the outlets, you probably want to limit your voltage drop on the generator cord alone to about 3%.

So, assuming a 12 gauge cord, you can probably have a length of about 85 feet before you run into trouble. Please note that these are rough calculations based on the voltage drop calculator referenced below. You can always extend the length of the cord by using heavier wire.

Here is a link that might be useful: Voltage drop calculator

    Bookmark   October 13, 2011 at 12:16PM
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Ron Natalie

Voltage drop is a function of the wire size (and what it's made out of) and current. I know kurto knows that but I wanted to make sure sarahlee understands.

    Bookmark   October 13, 2011 at 1:17PM
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Kurto and ronnatalie, thanks so much for your replies. I know very little about generators and voltage, and I appreciate your expertese.

I think forty feet would be the longest I'd need. Can I just buy one in a big box store, or would it be better to get it from an electrician? I hope we won't be needing to use the generator again any time soon, especially after the fun of last month's eight days with no power!

    Bookmark   October 13, 2011 at 8:11PM
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Assuming that this is a 240V generator, I'm not sure that you'll find a 40' extension cord at a big box store. The important thing is that the wires in the cord must be heavy enough for the load. Assuming there's a 20A @ 240V circuit breaker on the generator, you'll need 12 gauge cord.

    Bookmark   October 14, 2011 at 8:50AM
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here you go.

Here is a link that might be useful: locking cords

    Bookmark   October 14, 2011 at 10:11AM
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Kurto and Wayne440, thanks so much for your help.

I just took a look at the generator (as if I hadn't seen enough of it with 8 days without power!). It is actually an Onan 6500. It has several receptacles, including one that has 4 semi-circular slots and is labeled '120/240VAC, 30A, and another with three semi-circular slots that is labeled '120VAC/30A'. If I remember correctly, the one with four slots attaches to the house.

Does this information change the cord length requirements? Please excuse my ignorance - due to illness in my family, I've had to take on matters that I've never dealt with before.

    Bookmark   October 15, 2011 at 3:19PM
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The length that I quoted earlier was based on the assumption that you would be using an outlet that has 4 slots, and provides 120/240 service.

The extension cord will need to be 10 gauge, and terminated in a 14-30 plug and receptacle. There are two varieties of this plug and receptacle set; one that locks and one that doesn't. Make sure whatever you buy matches the plug and receptacle on your generator and house.

    Bookmark   October 15, 2011 at 10:06PM
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Look closely on the receptacle and it may tell you what it is (probably something like - L14-30). Most of the big box stores have generator cords available but they are usually only 25ft. If you have an immediate need, you could probably buy two and plug them together for a 50ft cord.

    Bookmark   October 16, 2011 at 9:17AM
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Kurto and wayne440, thanks so much for your advice! I've printed out your replies so I'll know exactly what 10 gauge cord to look for. I just hope I won't need to put that generator back into action any time soon - except for running it once a month, of course. Thanks again!

    Bookmark   October 17, 2011 at 2:19PM
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For most people running a small portable generator once a month is way overkill. If the owner manual allows running the fuel tank dry, I would run it annually with a small amount of fuel with stabilizer in the tank. I would run it for a half hour or so, with a load, letting the fuel run dry at the end. Drain the oil every year or two and refill. Put a little oil in the spark plug hole, crank a couple of times, reinstall the spark plug and forget about it for another year.

    Bookmark   October 18, 2011 at 3:28PM
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