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Best Extension Cord For Generator | Heavy Duty Gauge Recommendation

Generator Extension Cord

( Jump to specific extension cord recommendations )

( Jump to generator power cord Y-splitters )

The best extension cord for your generator is one that is specified to handle the power that’s being delivered between the generator itself and the device or devices plugged in.

I suspect that some people don’t know that it DOES MAKE A DIFFERENCE having the right or best extension cord (or cords) when powering appliances and other devices from a portable generator.

The portable generators come out during a power outage. Often the result of severe weather.

The most common temporary use is an extension cord for between a refrigerator and a generator. Maybe a chest freezer too. Some lights. Maybe even a furnace during winter, or air conditioner during summer.

Extension Cord Gauge | It Matters!

What difference does gauge make?

If the extension cord is ‘too small’,  it will likely restrict the power necessary to safely operate the loads that are plugged in. The cord, and the ends, will heat up.

What do I mean by ‘too small’? I mean the internal wires themselves. Wire is rated in “gauge”. Thick wire has more capacity for power than thin wire (logical).

Don’t let the thickness (appearance) of the extension cord fool you!

Generally, a thicker appearance (fatter cord) probably has heavier gauge wires inside. But that’s not always true! It could just be a thicker outer jacket. You’ve got to read the labels.

Check the gauge!

There are LOTS of extension cords that are #16 and #14 gauge. I recommend at least #12 gauge wire conductors in a extension cord used with a typical portable generator. Check the package. Somewhere on the label it will indicate the gauge.

The logic may seem backwards. But for wire gauge size, the smaller the gauge number (#), the more power (amps / watts) it can handle. So #12 gauge can handle more power than #14 gauge, etc..

NEC Ampacity Limits

The NEC (National Electrical Code) sets limits on the amount of Amps (current) that wire conductors may carry (for safety / overheating). There are variations depending on wire insulation/jacket, temperature, use.

The following is from NEC Table UL486E for copper conductors:
Not more than 3 conductors in cable.

WIRE GAUGEMAX AMPS
(Max 3 bundle)(Table: UL486E)
14 AWG15 Amps
12 AWG20 Amps
10 AWG30 Amps

Note: Extension cord specs vary (materials and other factors). Check the label!

There are a number of factors that contribute to the ratings for extension cords and they vary somewhat. Here are the specifications when applying ‘Ohms Law’ (P=IE) to the NEC wire gauge limits listed above.

14/3 extension cord

15 amps maximum
1800 watts @120 volts

12/3 extension cord

20 amps maximum
2400 watts @120 volts

10/3 extension cord

30 amps maximum
3600 watts @120 volts

Note: The “/3” simply means there are three wires within the insulation of the extension cord. One is for ground (green), one for “hot” (black), and the other for neutral (white).

How does length affect extension cord ratings?

Voltage drop. Most typical extension cords for outdoor use come in 25 foot and 50 foot lengths. All wire has some resistance (depends on conductor gauge, type and other factors). The longer the wire (extension cord) the more resistance (and voltage drop!).

With regard to a generator extension cord, in most cases you will be within 50 feet or less to run a cord from outside, through a window into the home (for example).

When is #10 gauge Extension Cord Better?

When you’re looking at 100 feet or longer, it (voltage drop) becomes potentially problematic depending on the appliance. In these cases it’s better to use a heavier gauge #10 extension cord.

Can I use 2 extension cords with a generator?

Yes, if your generator outputs more than one outlet circuit, the overall load may be balanced with an extension cord for each circuit.

For example, one of my generators is rated for 3500 watts. It has several conventional 120-volt outlets (and a high power multi-prong outlet). I might  use two 12/3 extension cords (one for each 120-volt outlet circuit) to deliver power inside the home to my various appliances if I need to.

Generator Power Y-Splitter Cord

A portable generator typically has a high power outlet which is multi-pronged (3 or 4 prongs, depending).

I use one of these Y-splitters on my own portable generator to split the high power output into  (2) 10/3 lighted outlets:

extension cord splitter for generator (10/4)

>> Generator Y-Splitter 10/4
(view on amzn)

Generator extension cord splitter ( 10/3 )

 
>> Generator Y-Splitter 10/3
(view on amzn)

Use Outdoor rated extension cords

Some are rated for indoor only use while others are designed for outdoor use. For use with a portable generator, you definitely want outdoor rated. The differences are in the insulation material, strength, and the ends themselves (plug & receptacle design).

Warning signs of overloaded extension cords

– extension cord becomes warm, very warm, or hot
– the generator circuit breaker keeps tripping
– your appliance is making a funny noise

The best extension cord for a generator?

A good general purpose choice is a 10/3 (#10 gauge) outdoor rated.

>> 10/3 50-Foot Triple Outlet Outdoor Rated Extension Cord

>> 12/3 50-Foot Best Rated Overall Outdoor Extension Cord
(view on amzn)

10/3 will perform better than 12/3 and NEC specs (listed above) indicate power handling up to 3600 watts. Additionally there will be less voltage drop under load. Theoretically enabling a longer run.

Tip: My experience has been that you are not going to find a 10/3 extension cord with a household style plug/outlet that lists its rating higher than 15 amps (or 20 amps with a T-blade plug) due to regulations (even though the #10 wire inside may be capable of handling the NEC rating).

3 outlet extension cord 50-feet heavy duty

30 Amp Generator Extension Cords

You can purchase specific 30 amp generator extension cords / cables. There are varying configurations.

Here’s one with 10 gauge wire that converts a 30-amp generator locking outlet to four 20-amp (120-volt) household outlets and extends your power up to 25 feet:

30 amp generator extension cord

>> 30-Amp Generator Extension Cord ( L14-30P to four 5-20R )
(view on amzn)

 
MORE:
30 amp Generator Cords
Generator Adapters

[ Read: Cold Weather Extension Cord That Remains Flexible & Won’t Crack ]

 
Read more:

Best Fuel Additive For Generators
Generator Maintenance For Preparedness
Generator Safety

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39 Comments

  1. Thanks for the reminder Ken. We need to replace one of our extension cords. I keep thinking about it, then forget it. This will help me get the proper size.

  2. Ken
    The third wire (usually green cover) is a ground – you might want to mention, if the generator is not grounded, what safety risks exist as you hold that power tool or appliance. But I am not an electrician.

    1. Check your generator’s Owners Manual. Some generators run on what’s called a floating neutral and don’t require being grounded.

  3. Also, there are some heavier gauge cords available that have an intergrated GFI. One should use these on small devices that don’t have an internal protection system from overload or on larger devices that you want some additional piece of mind for.

  4. Ya-all knew I would say something :-) :-)

    Extension Cord Safety;
    1. If the cord is crushed or has ‘nicks’; repair or replace it BEFORE you use it.
    2. If the Ground ‘prong’ on the male end of the cord is damaged or missing; repair or replace the end/cord
    3. Even if your appliance is not wired for with a Ground Wire; use a ‘Grounded’ extension Cord.
    4. Do NOT let the ends of the cords lay in water or get wet, you WILL fry.
    5. If you don’t know what you’re doing; DON’T do it, get help.
    6. If the cord ends are damaged at all or crushed; replace them NOW!
    7. Lastly, do NOT burn your home down or electrocute yourself/someone because you ‘improvised’ some foolishness with extension cords and electricity, BE SAFE!

    Remember just because you have a 100 foot code does not mean you need to use a 100 foot cord, use the shorter cord that will ‘carry the load’. Do NOT pinch a cord in a window or door when running the cord(s) into the house.
    Lastly, if you have a cord that’s to short, do NOT put the Generator inside !!!!!!

    Lecture over :-) :-)

  5. Pretty much never use anything less than 12/3, am a carpenter so use them daily, i used to have a bunch of 10/3 cords but they recently gave up, looking to replace them but am just going to make my own so bought a 250′ spool of 10/3 SO cable, will use Woodhead cord ends.

  6. Curious what the thoughts are with running the 12/3 then a power strip and 3/4 items off the strip. One is normally a fridge, then a few lights and radio. I never put more than one large appliance per extension cord , being window unit or fridge/freezer.

    1. RTW
      I would think you would need an industrial power strip/bar. All supply cords/devices should have the same capacity as the extension cord and if not grounded, you could become the live wire.

    2. It goes by amps. look at the rating stickers for the cord/power strip. Then look at the total of the items you want to plug in. The plug in items should be 80% or less of your cord/power strip max.

      cord = 15 amps then don’t plug in more then 12 amps total

    3. RTW
      Do not go over the amps of your power cord when plugging into a power strip.

      Add up the amperage of each item, which you would be using off of a heavy duty power strip. Do not forget about the ‘power surge(s)’ when an item is being used, or starting up of a major appliance.

      Example a fridge might have a running of 10 amps but the start up is 20 amps until it levels off. It is the start up that is the surge which causes the damage, most folks do not understand this rather important item, this was explained to me by our generator repairman years ago.
      (not an electrician)

  7. Good article. Good comments. Thanks, Ken. By the way, is there any way to know the rating of that old extension cord in the garage? I don’t see any markings whatsoever.

    1. Examine the cable carefully ideally under an illuminated magnifier. You should see molded in, or printed on the jacket something like 12-3, 14-3 or 16-3 along with other info on the cord. You have to look really closely to see it. Another good clue is the size and price. An extension cord that costs $15 and is only a little thicker than a pencil will most likely be 16-3. A better quality 12-3 cord might cost $50 and be nearly as thick as a magic marker, and noticeably heavier as well.

  8. One subject closely related to generator/extension cord useage is that of bonding between the ground and neutral there at the generator itself. Bonding refers to the ground wire and the neutral wire being electrically connected together there at the generator. The ground wire and neutral wire should only be connected together at one place in your house wireing, usually this is done in your house. Generator bonding is usually done at the factory and most people do not know this. This extra bonding will cause a ground loop to exist in your house wireing. See the National Electric Code why this extra bonding must be removed at the generator. I hope this is not confusing.

    1. I don’t think this would apply if you are just using extension cords and plug strips to distribute your generator power inside the house.
      If your generator is connected through a TRANSFER SWITCH to your house wiring (only safe way to connect a grid-connected house BTW) then this should be investigated further.

      1. Okay…..So my little generator is on wheels and when need it I roll it outside and plug it into a 220 volt outlet by my meter. Then I throw a manual disconnect switch which allows the generator to send power to the house after I start it. The line from the street is disconnected. When I see lights on at my neighbors I turn the generator off and reverse the switch. So am I going to burn my house down or electrocute one of my grandkids? I do have a ground wire that I run from the terminal on the generator to a grounding rod in the earth. This is worrisome. I paid a good chunk of change to get that disconnect added as I didn’t want to kill a lineman working down the street.

        1. It sounds like you have a transfer switch and not just a disconnect. A transfer switch typically is break-then-make, meaning it positively disconnects the household circuits from the grid connection, THEN it connects to the local generator circuit. The one I have uses a simple mechanical linkage and two double-pole breakers to accomplish this. (As you already know, what must absolutely be avoided is a situation where your generator is directly connected to the grid, which can kill linemen, since transformers work in either direction. It could also destroy your generator, which will see nearly a dead short.)
          How many prongs on the plug that goes between the generator and the house?

        2. OK your plug has 4 prongs, most likely 2 hot, one neutral, and one ground. This is the same as my 120/240v setup. My guess is that the reason code says you do not want a grounding loop is that some of the neutral current could flow in the ground conductor. Texas boy, or someone else with extensive electrical experience, could you please elaborate as to what exactly would happen in this situation?

    2. Unraveling the Confusion over Generator Power and Neutral Conductors

      How you should treat the neutral conductor depends on your system design. Neutral conductors must be grounded to prevent inadvertent potentials on conductive surfaces of equipment, enclosures and cable conduits and raceways. Alternate sources can make this process confusing, but referring to the NEC can help clear the problem up. Sec. 230.95 requires ground fault protection for solidly grounded wye.

      How you should treat the neutral conductor depends on your system design.

      Neutral conductors must be grounded to prevent inadvertent potentials on conductive surfaces of equipment, enclosures and cable conduits and raceways. Alternate sources can make this process confusing, but referring to the NEC can help clear the problem up. Sec. 230.95 requires ground fault protection for solidly grounded wye electrical services of more than 150V-to-ground, but not exceeding 600V phase-to-phase for service disconnects rated 1,000A or more.

      Why did this requirement come about? The most popular power system in commercial, industrial, and institutional facilities is 480/277V, 3-phase, 4-wire, wye-connected. Equipment design advances in the late ’60s resulted in a rise in popularity of 277V lighting systems. As more facilities installed these systems, the occurrence of electrical fires increased. Investigation showed that 277V systems increased the likelihood of arc faults to ground. Since arc faults have impedance, the phase overcurrent protection often would not detect these faults until significant damage had occurred. The NFPA responded by revising the NEC to include protection against arc ground faults.

      Since the expected current in an arc fault is considerably less than that of a line-to-line or line-to-neutral fault, phase overcurrent protection devices were taking too much time to recognize and interrupt the faults. In response, several manufacturers began producing ground fault arc current detection schemes that depended on the presence of a known return path for the arcing current to the power system neutral point. These schemes made it important to pay close attention to neutral conductor grounding.

  9. When I get a ‘bad’ extension cord, I cut it in pieces and throw it in the trash. That way no one will fish it out of the trash and use it. I do the same with welding hoses.
    Ken, it might be good to point out that the different sizse of wire will carry different amp loads at 220 volts, like when you are using a welder or a well pump on 220v.

  10. I use a 50′ 10/3 to get from the generator (which is far outside) into the house. From there I’ll go 12/3.

  11. Hello I do not post much but I just happen to be a master electrician and feel a little obligation to this.

    1. Most all portable generators have a ground lug on them. If not one should be installed on the frame. You should connect the grounding lug to a ground rod with ground wire. This is usually near your electrical meter. You need this ground to get a proper neutral and for your safety. Do not count on the generator sitting on the ground to give you a good ground.

    2. You should use a quality electrical meter to check the voltage of your generator. Check the hot wire (black) most of the time to the neutral wire (white) and then check the black to ground wire (green). You should have between 110volts and 125 volts AC. To check 220 volts use the same method but add checking the second black (some times red) to the other black wire. You should have between 212 volts and 230 volts AC. The reason for this is to keep from frying up your stuff. And having the info for the math I am going to give you.

    Now you can use your generator.

    3. Extension cords. Bigger is better. Ken and several of the comments are correct with their info. I would like to add. For every 100 feet you will have a voltage drop of 1 to 3 volts depending on the quality of the wire in the cord and the cord itself. To figure out amps you must divide watts by volts to get amps. This is why you checked the voltage earlier. So if your microwave runs at 1800 watts and your generator is putting out 123 vac. You are using 14.63 amps. Terms you should know FLA-full load amps usually start up amps. RLA-rated load amps, usually running amps to keep it simple.

    4. If you connect your generator to your house please always check to make sure your main breaker is off. The transformers the power company uses work both ways thousands of volts in 120/240 to your house, your generator 120/240 out to the transformer thousands of volts to the power lines. And the power company linemen really do not like that.

    There is more but this should keep you safe.

    1. Exactly, and never use an ungrounded generator!
      There were several deaths here because of ungrounded generators.
      Always happens after a storm, also a lineman was electrocuted from a generator being back feed to a house.
      Always read and understand the owners manual with your generator.
      Be safe!

  12. When I was working in lighting we had many sales meetings with the sales reps and wire/cable was explained to us like it is a highway. The more lanes you have the less congestion. Same with wire the larger the gauge, which is a smaller number, the easier power travels so to speak. I purchased a 20 amp cord for the freeze dryer because the dryer will at times pull 16 amps. Also it is plugged into a 20 amp socket. This was suggested by the Harvest Right salesman. Found a 20 amp without bells and whistles on Amazon. Could not find one at any local store.

  13. I never use anything under 12/3
    Typicaly for feeds off the generator i go minimum 10/3 or 10/4 type SO, for the trunk from my big generator i have a 6/4 type SO cable i made up, it goes into breaker panel and disconnect

  14. Lots of good info in the article and in the comments.

    I would add one thing, get a few spare cords and high amperage ends.

    I like Hubble brand of cord ends, good stuff that is well made.

  15. Re reading this brought back some memories. One of the marinas where I lived on my boat had 20 amp service on the docks. Most marinas have 30 amp service and when you think about it a single 30 amp plug doesn’t allow you to pull much power for the needs of living aboard a boat. 20 amp was even worse. What some folks did was remove the 20 amp breakers in the power boxes on the dock and put 30 amp breakers in. The wiring wasn’t designed for this so as people at the beginning of the service started pulling more power (amps) resistance further down the system started going up and voltage started going down. Result was boats were catching on fire from the heat from the increased resistance in the outlets on the boats. No lives were lost but one fellow was seriously burned.

  16. I’ll be using a portable 3600 Watt generator during a storm, is it okay to connect two 25 ft extension cords together to power the refrigerator I want to use if we lose power.

    1. Alan:
      Depends on the “gauge” of the cord.
      Do not use anything smaller than 16 gage for sure. 12ga is better. But as Matt said, keep an eye on them, better if you could not use 2.

  17. I use the flat style 25ft.10 Gauge 30-Amp Generator Extension Cord L14-30P to four 5-20R from the generator into the house. Then I use a 25ft 12/3 gauge 5-20 cord for longer runs from that. Then I use various lengths 14/3 gauge 5-20 cords to branch out to whatever needs powering. There are 2 exceptions being that I use a 15ft. 12 gauge to power the refrigerator and a complete separate 50ft. 12/3 from the generator to the NG heater. So everything that I need power for is taken care of by 2 connections at the genset.

  18. Hi, since we are on generator extension cords, i have a question or two for anyone. I have a champion 5500 watt new generator. My goal was to run a old refrigerator and new 10,000 btu portable ac unit dual duct . I have been concern because of the manual that warns do not us extension cords. I get it ! But i thought they did that for warranty and liability and safety reason. I missed that before purchasing. BLA! Having said that, i bought 2 100 foot
    10 awg extentions cords. One 30 amp splitter , for the portable AC UNIT. Since portable AC has a mother board i am assuming fluctuations could issue so i also purchased a industrial surge protector with a 12 awg cord to match AC unit which will get its power from the 10 awg 100 foot cord coming from the generator. Just wondering would anyone like to comment ? Will this work ? Or send back unit and start over???

    1. Walter,
      Disclaimer: This is not advice. Rather, opinion. That said, What you have described sounds like it will work. There’s nothing out of spec in my view, based on what you’ve said. I don’t know if your run is 100 or 200 feet. However you did the right thing by purchasing 10 AWG cord. Therefore your losses will not be too bad.

  19. Hi All,
    I just purchased a Duromax 12,000w startup/9,500w running portable generator. The electricians in my area are extremely busy this year. None are available to install an interlock switch or transfer switch so during outages this winter I plan to run extension cord/s into the house to power the fridge and a couple space heaters. Any recommendations for extension cord brand or type that would best fit my needs? Thanks in advance!

  20. Appreciate how easy explanations were. I now can get a cord for my appliances and safety. Tired of cords over heating even when they looked(?) and cost so much! Thanks again

  21. Thanks. I would guess that gasoline consumption would be better usimg a thicker appropriate extension chord?

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