Welcome. Choosing the right generator extension cord can be confusing if you don’t know what to look for. I wrote this guide to help buy the correct extension cord to match your generator.
We seldom give an extension cord much thought. This is something we take for granted, yet we use them all the time. Few actually understand extension cord safety. Are you using the right product for the amps, or cord length? When it comes to generator extension cords, things can become a little more complicated.
Choosing Your Generator Extension Cord
Using a generator at home, on a jobsite, or for camping invariably requires extension cords. In most cases, you will need to cover quite a distance as the generator is seldom close to where you’re using the power. You obviously want a generator extension cord that is convenient and easy to use. Although we don’t always realize the risks involved, safety is (or at least should be) the main concern.
Because generators are typically used outdoors, you need to be more aware of the potential dangers than you would using one indoors for normal household applications. Typically, the extension cords used with a generator have to handle more current than those used in the home. If you’re using your generator to supply your home during an outage, you need to be certain that the extension cord can handle the load.
This article is going to serve as a guide on everything you need to know about generator extension cords, splitters, adapters, and the all-important safety considerations.
What size extension cord do you need for your generator?
You may be using one extension cord or several. It will depend on what you’re using the generator for. On a jobsite, you will often find many extension cords, some connected to others, or split to supply several areas. Linking extension cords together can become a hazard, as I’ll explain when discussing the gauge vs length requirements for a generator extension cord. Using an extension cord to connect a 30A or 50A supply to your home requires more detailed calculations for the load you’re using. The same would apply when deciding which would be the best RV generator extension cord.
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We have to understand the importance of distance in relation to current if we’re going to use extension cords safely. This applies, not only to generators, but also for use around the home, garage, workshop, or garden. Overloading an extension cord can easily result in fire, possibly even electrocution.
When determining the size of an extension cord we need to consider the length of the cord and its thickness. In other words, the gauge of the electrical conductor. Different metals are used for electrical conductors. Various metals have differing electrical impedance. Perhaps, I should first take some time to explain this.
Most extension cords use a conductor made of copper. This is a reasonably good conductor, with relatively low impedance. This means that copper does not have as much resistance as many other metals and will, therefore, not generate as much heat as a metal with higher impedance. However, copper is not the best conductor. Because copper is relatively inexpensive, it is the popular choice. Essentially, copper is the most cost-effective metal to use. It is quite cheap and is pretty efficient as an electrical conductor. If we use a more expensive metal, like aluminum or silver, we have a better conductor. This means lower impedance which won’t require the same gauge as a copper wire.
From this understanding of the conductivity of metals we can deduce the following. A copper conductor needs to be thicker than a metal like silver for the same current. Since most extension cords are made of copper, the standard gauges are provided for copper wire.
We measure an electric current using the Ampere (A) unit of measurement. This is commonly referred to as Amps. Amperes tells us how much current we are using. The power of an appliance (measured in watts) is equal to the amps multiplied by the voltage. To determine the amps required for a 125V 2,000W heater, we divide the wattage by the voltage. This would be 16.67A.
The electrical outlets in your home are rated for the amps that can be safely supplied by the copper wire that connects that outlet to your main breaker panel. A circuit breaker is used to ensure that you never exceed the safe maximum current for that circuit. A 125V 20A circuit can supply a maximum of 2,400W before the breaker trips. This is because electrical current generates heat. As the amps increase, more heat is generated.
Once you exceed the amperage that a metal is capable of safely conducting, the resultant heat will cause the insulation to melt. Amperage can reach a point where it generates enough heat to melt the metal conductor. This is the principle of an arc welder, using high electrical amperage to melt metal.
Now things may get a little complicated. Though there’s no need to despair, I’ll explain everything as we proceed.
The Amp rating for a 20A electrical outlet, is only relevant at the point of the outlet. As we increase the distance from the breaker box, the safe amperage that we can use is reduced. If your extension cord is too long, the impedance of the wire will reduce the amount of amps you can load onto that cord.
Now, it’s time to look at why the distance from the generator, or breaker panel, is so important. This means understanding electrical impedance and its effect on a conductor.
What is impedance?
Electrical impedance is the resistance within the conductor, measured in Ohms (Ω). Resistance to the electric current produces heat. Perhaps you’re starting to see a common thread here. Increasing the amps causes the extension to generate heat which may become dangerously high. Increasing the impedance generates additional heat, thereby increasing the risk of melting the insulation, or conductor, causing a fire.
I started out by discussing the impedance of various conductors, now this might begin to make more sense. Regardless of the metal used, the thickness of the wire (or gauge) needs to able to withstand the amount of current without overheating. If you’re conducting a high amp current, over a longer distance, you will need a thicker (lower gauge) wire to allow for increased electric flow. Just as a thicker pipe will allow for more water to flow through it (with less resistance), so a thicker wire will allow more current to flow through it, with lower impedance.
Gauge vs Distance
Based on the principles of electric current and impedance we now know the following: an electric conductor can supply a maximum current over a distance relative to the thickness, or gauge, of the conductor.
If an extension cord is rated at 20A, it means that it can be used safely for the specified length of that cord. If you connect one 20A extension cord to another, you’re increasing the distance, thereby increasing the impedance. In doing so, you run the risk of overheating the extension cord. The increased length will result in more heat being generated by the higher impedance within the conductors. It is of greatest importance to understand this relationship between the gauge vs distance, if you’re going to use any generator extension cord safely.
Here are few practical examples to illustrate the principles we’ve discussed.
- A copper 25’ extension cord, rated for 20A @ 125V, needs a #14 wire. For a 25’ 50A extension cord, a #10 wire would be required.
- A copper 50’ extension cord, rated for 20A @ 125V, needs a #12 wire. For a 50’ 50A extension cord, a #6 wire would be required.
- A copper 100’ extension cord, rated for 20A @ 125V, needs a #10 wire. For a 100’ 50A extension cord, a #4 wire would be required.
By increasing either the amps or length, the wire gauge will need to increase accordingly. Take note that a lower gauge wire is thicker. This means #6 wire is thicker than #10.
So far we’ve only looked at 125V extension cords. If you’re using a 125V/250V generator, things become even more complicated.
125V/250V Generator Extension Cords
A generator capable of supplying 125V and 250V AC power utilizes a 2-pole alternator. Each pole generates 125V. When the poles are connected to the outlets independently, the power supplied will be 125V. If both poles are connected to the same outlet, the power supplied will be 250V. The outlet will also have a neutral connection and, usually, a ground.
An outlet supplying 125V, will have at least 2 prongs, one hot and one neutral, a third (ground) prong is common. An outlet supplying 250V will have at least 3 prongs, 2 hot and one neutral, with a 4th ground prong in most cases.
The amperage supplied by the generator will be the same at each pole. If the maximum rated amps for a generator is 30A, it means that each pole can supply a maximum of 30A. When two poles used in parallel (250V), the total available amps will be 30A. Used independently (to supply 120A) each pole will still supply 30A, providing a total of 60A at 125V.
An extension cord used to supply 250V, requires two hot wires, whereas a 125V extension cord requires only one hot wire. This extra wire, used for a 250V extension cord, reduces the load on each wire. The current is now conducted along 2 wires instead of one. Because of the increased voltage, the percentage voltage drop over the distance is less for a 250V extension cord. This means a 250V extension cord can use thinner wire for the same amps.
From the above example, we know that a 125V, 50’, 20A extension cord requires #12 wire. The same extension cord, with an additional wire used for 250V, will only require #14 wire.
Although a 250V extension cord will always be thicker than a 125V equivalent, because of the need for an additional wire, the thickness of the actual wires inside the cord will be less for the 250V extension cord.
Using 250V is more efficient, which is why is why high-watt appliances usually use a higher voltage. A 2,000W heater, drawing 16.67A at 125V, will draw half as much at 250V (8.33A).
Using an extension cord safely
Based on what has already been discussed here, we need to observe the number one rule for buying and using an extension cord safely. The extension cord must be the correct gauge for the amps and length of the cord. This means you should never extend the cord beyond the amp rating.
You can calculate your end usage and determine if a longer cord can be used safely. Say , for example, you’re using a 20A extension cord to supply a 10A load, you will be able to use a longer cord because you are not utilizing the full 20A rated for that cord. You can calculate your load by dividing the watt rating for the appliance by the voltage.
Apart from ensuring that you use the correct extension cord for the load, there are several other considerations. Generator extension cords have there own safety requirements relating to the unique conditions pertaining to gas generators.
Using an Extension Cord in the Home
Inside the home, or any building, is the safest place to use an extension cord. You don’t have to worry about weather conditions and other hazards associated with outdoor use, or the additional precautions required for a generator.
Always run your extension cord along a wall, not crossing the floor. It easy for people to trip over the cord. It can also be a danger for anything moving across the floor, like a vacuum cleaner. An extension cord should never be placed under rugs as this is a fire hazard and the cord could be damaged without it being noticed.
An extension cord should not be used close to running water or drains. It is always best not allow the connectors to lie directly on the floor where water may be spilled or be exposed to flooding. Be cautious when using extension cords around heating equipment, like space heaters. Always ensure a safe distance between the cord and the source of the heat, as this could cause the insulation to melt.
Using your Generator Extension Outdoors
We often use extension cords to supply a lawnmower and other outdoor equipment. Outdoor events, tailgating, and camping, are also instances where we’re likely to use extension cords. For outdoor use, we need take note of the environment and how this may affect the safe use of the cords and electrical equipment.
The risks relating outdoor use of extension cords and appliances, or tools, is mostly about moisture. Even when it is not raining, moisture can collect outdoors. Using electricity in the presence of any type of moisture is hazardous. One cannot always avoid moisture completely, the lawn is often damp, as is the soil around the yard. Avoid placing an extension cord in water. Always make sure all connections, like plugs, splitters, and outlets, are not placed directly on the ground. This may expose them to water or moisture, which will ultimately result in a short circuit.
Never use an extension cord in rain or snow. Ensure that an extension cord used outdoors is plugged into a GFCI protected outlet to reduce the risk of electrocution through contact with water or damage to the cord.
Using an Extension Cord with a Generator
Depending on the generator power application, all of the above precautions may apply to generator extension cords. There are some others that relate specifically to generators.
The generator engine and muffler become dangerously hot. You need to be aware of this when using extension cords for a generator. Ensure that the cords are not too close to hot or moving parts.
A generator may sometimes move as a result of vibration. Be aware of this. Make sure that there is sufficient length and allow for a distance from the generator frame to prevent any damage that may occur if the frame exerts pressure on the cord.
General Precautions : Generator Extension Cord
Regularly inspect your extension cords for damage. Broken insulation or damaged connectors are dangerous.
Never use an extension cord when coiled or knotted. Electricity conducted through tightly wound extension cords generates extra heat which will damage the extension cord over time. Knots in the extension cord will have a similar effect.
Always keep the extension cord dry and avoid high temperatures close to the cord when using or storing it.
Replace damaged extension cords. Attempting to repair extension cords with electrical tape is not safe for long term use. It is only a temporary measure and should be avoided unless in an emergency.
Tips for Buying A Generator Extension Cord
There is a vast difference between cheap extension cords and those that cost a bit more. A lot can be said for the quality of plastics used for connectors and insulation.
A thick outer insulator will ensure that an extension cord is going to last longer and be safer to use. It is less likely to be damaged by usual wear if the plastic is of a higher grade.
You want a good deal of flexibility. The cord must be easy to roll and unroll. Thicker, more flexible extension cords are less likely to become tangled, greatly reducing the frustration that comes from constantly detangling the cord.
Generator outlets are not always the same. You will require the correct type of plug for the outlet you intend using to supply your extension cord. You may need an adapter to use a specific type of plug for the outlet fitted to your generator.
Industry standards for power outlets and connectors, used in the North America, are managed by the National Electrical Manufacturers Association (NEMA). This provides a standard for electrical outlets and the plugs used to connect appliances and extension cords to the outlet.
While there well over 40 listings for various types of NEMA outlets, there are two basic types of outlet, locking and non-locking outlets. All NEMA outlets and connectors are classified using an Alpha Numeric designation. If the letter “L” appears at the beginning of the NEMA designation, it means that it is a locking outlet. The letters “TT” at the beginning stand for Travel Trailer, commonly known as an RV outlet.
The first Number indicates the voltage classification, and the number of wires that can be connected to the outlet (NEMA 1 – 24). The first number is followed by a hyphen (dash), with the next number indicating the amp rating for the outlet. The amperage designation can be followed by the letter “R” or “P”. The letter “R” stands for receptacle, and “P” for plug. While both are basically the same type of outlet, the difference between R and P outlets has to do with configuration, angle, and size of the blades , or prongs. Both types of outlets perform the same function but cannot be used interchangeably. The plug has to match the outlet.
Identifying the most common NEMA outlets by Numeric Category:
Since many of the NEMA outlets (and connectors) are used for industrial applications, this will be an abbreviated list of more common NEMA outlets and plugs used for domestic applications and portable generators.
- NEMA 1: Two prong 125V outlets: hot and neutral, with no grounding.
- NEMA 2: Two Prong 250V outlets: 2 X hot, with no grounding.
- NEMA 5: three prong 125V outlets: hot, neutral, and ground.
- NEMA 10: three prong 125V/250V outlets: 2 X hot, neutral, with no grounding.
- NEMA 14: 4 prong 125V/250V outlets: 2 X hot, neutral, and ground.
- NEMA TT: 3 prong RV 125V outlet: hot, neutral, and ground.
Outlets with no grounding have become less common, as modern building regulations require that all permanent electrical installations include a ground wire. OSHA regulations also require that jobsite generators be protected by Ground Fault Circuit Interrupters (GFCI), which requires a ground wire connection.
The amperage for 125V household and generator NEMA outlets normally range from 15A – 30A. For example, NEMA 5-20R, which is a 125V 20A receptacle. The most commonly used 125V/250V outlets are NEMA 14, usually 30A or 50A, and are generally locking outlets (EG. L14-30). RV (TT) outlets are always 125V, 30A (TT-30).
Splitters and Adapters
Smaller generators, with an output of less 30A, are usually fitted with only NEMA 5-15 (125V 15A), or NEMA 5-20 (125V 20A) outlets. Larger generators can have any variety of outlets for 125V, 125/250V, and 125V RV outlets, ranging from 20A to 50A, sometimes more. When using an extension cord, you will often be using various types of splitters and adapters.
Probably the most common adapter is used to convert a NEMA 5 or 14 outlet to a TT plug for RVs. Though basically all common types of NEMA outlets have adapters that allow you to use just about any 125V, 250V, or 125V/250V outlet to supply any type of NEMA extension cord.
Splitters allow you to increase the number outlets that you can use. These are common and are used for a variety of applications, from AC extension cords, to audio and digital signal cables and outlets. There are three common terms used to describe various types of splitters. AC splitters are most commonly used in the NEMA 1 and 5 configuration, but they can also be found for other types of outlets.
This is a general description of most splitters, meaning that one plug will have two or more cords connected to it, each supplying additional outlets. Fan-style splitters are used in two common formats:
- W-Splitters consist of a male plug, split to 3 female outlets, allowing a single outlet to supply 3 extension cords or appliances.
- Y-Splitters consist of a male plug, split to 2 female outlets, allowing a single outlet to supply 2 extension cords or appliances.