A special message for my friends –

With the types and number of storms we’ve been getting, you might be looking for a new generator, or hauling out the one you’ve been storing in the garage.  Unless you already have a transfer switch, you don’t want to be caught off guard with an inadequate generator extension cord.  Make sure that it is of sufficient gauge and length for your purposes.  Remember, you must keep the running generator AWAY from any living space.  Don’t put your family in jeopardy because your cord is too short.  ALWAYS be safe.

What Are the Differences?

Coleman 100ft 15A Extension cord for generator

Standard outdoor three prong 5-15 male and female ends

Here you will find out what you need to know about extension cords for portable generators.  These are also referred to as generator cords.

How do you understand gauge wire sizes and how does it relate to the length of cord?  What’s the difference between a four prong extension cord and a three prong one?  What does AWG mean?  These are the most common question and you will find your answers on this article.

You probably have extension cords of different gauges and lengths lying around the house and in your garage.  But are they suitable for use with your portable generator?

You know that for safety and the possibility of Carbon Monoxide poisoning, you have to operate your portable generator at least 20 feet from your home and never in a basement or garage.  So if you’re using it for powering devices in your home, that means you’ll need long generator cords to run appliances in your home, right?

So why can’t any old cord do as long as the plug fits?  Should you care how long the cord is?  The answer is YES!  First, we’ll have to look at how cords are rated.  And then there are those plug configurations that we’ll need to understand.  Above all, we’ll want to insure the safety of our families and ourselves.  Ready?

If you feel the need to look at the wide variety of generator cords (and household types), there is no better location to search for just about any extension cord you could need than at Amazon.com.

Don’t expect that your local hardware or home improvement store will have a large enough selection.  You can browse when you’re ready by clicking the Amazon button, and type in some of the descriptors that you’ll be reading below:




How Do Gauge and Length Correlate?

Extension cords contain copper wire through the center that varies in thickness.  The thickness is rated by American Wire Gauge (AWG).  Most common are AWG 16, AWG 14, AWG 12, AWG 10, and AWG 8, with the lower the number, the thicker the wire, or bundle of wire.  The thicker the wire, the more watts you can expect to power through it. For example, a thin standard cord for a wall lamp which you’ll have in your home, which doesn’t need much power is probably AWG18 wire with only a two pronged plug.

But you should know that depending on the Amp draw or wattage of your appliance, the gauge of the wire in your extension cords becomes a factor in the length of the cord you can use.  Because a wire can cause resistance to the power flow and the thinner the wire, the more the resistance.  Similarly, the longer the wire, the more the resistance.

In order for your electrical device to operate efficiently and safely, it must get the full power that it needs.  You could even damage the device.  If the resistance due to the cord thickness or length keeps the device from getting what it needs, you have to increase the thickness of the wire (lower number AWG), or shorten the cord. The lower the gauge AWG number (thicker the wire), the longer the cord you can use to supply power to identical devices.  Take a look at the table below:

Wire Gauge Requirements

Device Requirements and Maximum Cord Length (ft) by Wire Gauge
AmpsWatts (120V)Watts (240V)#8 wire#10 wire#12 wire#14 wire#16 wire

Let’s say you are going to run an appliance with a 10 Amp draw on 120 Volts.  That equates to 1200 watts if you remember the formula that Watts = Volts x Amps.  If your extension cord is #16 gauge wire, you can have a cord up to 50 feet.  For the same appliance, if your cord is #10 gauge, your maximum length is 250 feet.  Now very few households have extension cords this long, but on-site work can often mean that the portable generator will be located 100’s of feet from the power need.  And lower gauge extension cords are very expensive.  You’ll have to decide what is best for your needs.

Guidelines for the Size of Generator Cords

National Electric Code (NEC) guidelines on amperage determine the gauge or wire that you want to use, and resistance determines the length. All wire has resistance which will lower your voltage over distance so if you have to go far then you need to step up your gauge.

Examples of Amperage limits are…

  • 16g = 10 amps
  • 14g = 15 amps
  • 12g = 20 amps
  • 10g = 30 amps

Always follow all safety guidelines when using extension cords and electrical cords in general.  If you tried to use an extension cord with #16 AWG for an appliance which draws 15 amps, the cord may get very hot and create a fire hazard.  Always look for the Underwriters Laboratory (UL) label which is permanently attached or molded into the cord.  Read the label for instructions and electrical rating.  A “W” on the plug will tell you that it is rated for outdoor use.  See below for other letters which describe your cord.

Be safe.  If you don’t have adequate extension cords for your portable generator, take the expense to purchase one.  Safety does not come with a price tag.  Get cords that will do the job safely.  Most portable generators with dual 120V/240V power have a L14/30R receptacle.  L14/30R and other outlet/plug designations are explained in more detail below.

Since they mostly supply a maximum 30Amps from the outlet, some have opted to step up to a 50Amp cord, but this can be pricey.  The cord below is a safe choice for running several devices off of your L14/30R in most 120V/240V portable generators.  This type can be rated for 300V, so as long as you don’t attach more than 30 Amps total, you’re good.  The cord pictured is made by Westinghouse and is available at Amazon among other places.

Westinghouse WGC extension cord for portable generators

Westinghouse 25 ft 10 gauge with L14-30 plug and four 5-15R receptacles, rated for 300v

You will come across several extension cord types when you shop around.  Typically a standard three prong (5-20A) male will have a standard three prong female at the other end.

male to male cord is unsafeNEVER use a male to male cord.  These are highly dangerous and might even be illegal.  Imagine plugging into your home outlet.  This is an exposed LIVE end.  Imagine accidental contact with this live end.  Worse yet, imagine a small child putting the live end in his or her mouth.  NEVER!

You would need this type of cord to connect directly into a wall outlet from your generator.  Remember you should not connect your generator to your home through a wall outlet.  This is highly dangerous as it could back-feed a power line that an electrical worker assumes is down.  Never buy one.  Never construct one.  Always be safe.

Be aware if you use a split ended cord, that even though you can plug in more devices at the end of the cord, the same maximum amps are available through the main cord and the multiple female receptacles will share the power.  You must remember to not overload.

PowerFit PF922530 25ft extension cord

PowerFit 25 ft 30 Amp with L14-30 plug and four 5-15R receptacles with two in-line breakers

Use the heavier three or four prong locking cords when you plan to split the work at the other end.  Some cords have added safety by including in-line breakers.

Normal extension cord safety should be mentioned.  You know the drill.  Never use damaged or frayed cords or risk electrocution or fire.  Never place rugs, carpet or any item on top of an extension cord.  Never plug a generator into your home via a wall outlet.  For other general safety ideas, check out the article on this site How to Safely Use a Portable Generator.

Portable Generator Outlet Types

NEMA is the acronym for the National Electrical Manufacturers Association.  NEMA connectors are AC power plugs used for electrical outlets in North America and other countries that use the standards set by the US.  The NEMA 5–15R is the standard electricity outlet found in almost every household and building in the United States.

NEMA wiring devices are made in current ratings from 15 to 60 amperes, and voltage ratings from 125 to 600 volts.  Different combinations of contact blade widths, shapes, orientation, and dimensions give non-interchangeable connectors that are unique to a particular voltage, current capacity, and grounding system.  NEMA 1 (two prong) and NEMA 5 (three prong) are what we’re used to seeing around the house.

NEMA outlet chart - extension cords for portable generatorsThere are two basic classifications for a NEMA device: straight-blade and locking.  The straight-blade 5–15 and 5–20 are found nearly everywhere in countries using the NEMA standards, and are intended for supplying lighter-duty, general-purpose electrical devices.

Twist-locking types are used for heavy industrial and commercial equipment, where increased protection against accidental disconnection is required.  As with hooking to your homes panel with a transfer switch.  See the article on transfer switches on this site.  Numbers prefixed by “L” are curved-blade, twist-locking connectors; others are straight blade and non-locking.

The numeral preceding the hyphen in NEMA nomenclature indicates the configuration, that is, the number of poles, number of wires, voltage, and whether single- or three-phase.  A grounding type of device is described as two-pole, three-wire; or four-pole, five-wire; etc. A non-grounding device may be two-pole, two-wire; or three-pole, three-wire; etc.  Make sense?

The numeral following the hyphen is the rating of the device in amperes. The number is followed by the letter R to indicate a receptacle (female connector) or the letter P to indicate a plug (male connector).

As an example, the 5-15R is the common 125 V two-pole, three-wire receptacle. The L5–15R, while sharing the same electrical rating, is a locking design that won’t fit with the straight-blade 5–15 design. The 5–30 has the same two-pole, three-wire configuration and 125 V rating, but is rated 30 A.  Notice that 125V is commonly mentioned here, but 120V is the common current that can fluctuate upward and downward when supplied by a portable generator.

Although there are several non-grounding device types in the NEMA standards, only three of them are in widespread use today due to safety issues. These are the two-pole 1-15, still in use in millions of buildings built before the 1960s, and the three-pole 10–30 and 10–50.  You can use the 1-15 in a 5-15R or 5-20R.

When shopping for portable generators, the predominant outlets are the 5-20R and the L5-20R or L14-30R.  You will find some with RV receptacles and numerous with a DC receptacle for 12volt charging.  Remember to match the receptacle on your generator with the plug of the extension cord.  Never use a cord that was not intended for its purpose.

Extension cords champion 46539

Champion model 46539

extension cords duromax

Duromax model xp4400e

Notice on the left on the Champion model, and on the right the Duromax model have the standard three prong 5-20R outlets.  But the larger outlets are different.

On the Champion you’ll find a common three prong locking 120 volt L5-30R and the three prong 120 volt TT-30R.  The TT (travel trailer) is common on RV’s.  On the Duromax model you see the four prong 120/240 volt locking L14-30R.


DC plugs can be more difficult to find, depending on the receptacle type on your generator.  Some have two prong offset plugs, some have a cigarette lighter plug type, some simple positive and negative end wires.  Hopefully, if you purchase a generator with DC capability, the unit will come with a DC cord included.

Extension cord information can be confusing the first time through, as it was for me.  Take your time on this.  Make the right choice for your generator and the uses that you plan for it.  Most importantly, make sure that you have the right gauge for what you plant to run, AND sufficient length.  You’ll want at least 25 feet, but can’t go wrong with 75 feet to 100 feet as long as the gauge is 10awg.  You’ll find many uses for your cord that you may not have expected.

Generator Cord Varieties

OK, here is the nomenclature that most don’t need to know, but the Generator Grader prides itself in providing all of the education that you could use.  You may come across a series of letters describing your generator cord like SJ, SJT, SEOW, SO and others.  Each has an application and materials associated with it.

The cord could be made of thermoset, thermoplastic elastomer, or thermoplastic.  Thermoset cords have heavy-duty  rubber jackets and are very sturdy.  Thermoplastic elastomer cords are medium-duty and work well in cold environments.  Thermoplastic cords are light-duty.

Here are what the letters mean.  The nomenclature may be any combination and will determine its best use:

  • S = Severe Service Cord – 600 volts
  • SJ = Junior Severe Service – 300 volts
  • T = Thermoplastic
  • H = Heat Resistant
  • N = Nylon Outer Jacket Material
  • E = Elastomer – thermoplastic that looks and feels like rubber
  • O = Oil Resistant Outer Jacket
  • OO = Oil Resistant Outer Jacket and Oil Resistant Insulation
  • V = Vacuum (typically for vacuum cleaners)
  • W = CSA Weather and Water Resistant (for indoor and outdoor use)

Well, that’s about it.  Check out hundreds of styles and lengths available.  Happy browsing.  While you’re at it, you might want to check out the 5 gallon gas containers, funnels, fuel stabilizer and generator covers to have everything you’ll eventually need.



Filed under: Understanding Cords & Outlets