Generator Extension Cord
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 generator comes out during a power outage, often the result of severe weather. Probably the most common temporary use is an extension cord for refrigerator to generator. Maybe a chest freezer. 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 GAUGE||MAX AMPS|
|(Max 3 bundle)||(Table: UL486E)|
|14 AWG||15 Amps|
|12 AWG||20 Amps|
|10 AWG||30 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.
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:
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 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).
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: