How to Backfeed a Generator
Safety is paramount when it comes to powering our homes. Some homeowners use generators to restore electricity to all or part of their homes during power outages or blackouts. There is more than one way to connect a generator, and choosing the safest method ensures that no one is injured and prevents property damage to you or a neighbor.
One method known as backfeeding connects a generator directly to a home’s electrical system. A homemade generator cord supplies power from the generator. One end plugs into the generator, and the other end plugs into an outlet inside the house. Dryer outlets are popular because they accept a 240-volt connection which allows powering the entire home instead of only a portion. Smaller generators may not have a 240-volt outlet and therefore, the outlet inside the house is a regular 120-volt household convenience outlet.
Warning: Backfeeding your home with a generator is illegal in most jurisdictions and was effectively outlawed by the National Electrical Code. You could be held criminally liable for injury to others or damages caused by backfeeding. Communities have passed laws prohibiting homeowners from using a generator to backfeed their home.
What is Backfeeding?
Backfeeding connects a power source to deliver power in the opposite direction. Usually, a household receptacle is a source of power for an appliance. Plug in the appliance and it works. Power from the utility enters the main circuit breaker panel, goes through a circuit breaker that protects the wiring against overloads, and then through the receptacle to power the appliance.
When backfeeding, electricity flows in the opposite direction from normal.
A generator backfeed connects the house to a generator using a cord with two male plugs, usually homemade, to connect the generator to an outlet in the house. Power flows into the outlet, to any other outlets on the same circuit as the backfeed receptacle, and through the circuit breaker panel, and from there throughout the house and also out of the house utility lines, through the transformer where it gets stepped up to the distribution voltage—as high as 50,000 volts.
The Dangers of Backfeeding a House
If you ever accidentally shocked yourself, you know that the result could range from mildly annoying to extremely painful. Electric generators produce electricity at voltages that can cause severe burns, injury, and even death.
Always read the owner manual, including the safety warnings. Heed the safety stickers on the generator.
Follow Portable Generator Safety Rules
Risk of Electrocution: Backfeeding introduces risks of electrocution in two ways.
Electrocute [ ih-lek-truh-kyoot ] (definition by Dictionary.Com)
(1) to kill by electricity.
(2) to execute (a criminal) by electricity, as in an electric chair.
- The homemade generator extension cord has two male plugs instead of a plug and and receptacle. The homemade cord plugs into the generator receptacle and into the receptacle inside the house. When the generator is running, the plug inside the house is hot. Anyone touching that plug risks electrocution. If someone trips on a cord—another risk of using extension cords—the plug may come out of the outlet, touch the person who tripped over it, and shock or electrocute them.
- Electricity flows through the main circuit breaker to the utility transformer which steps it up to distribution voltage—thousands of volts. Downed lines nearby become energized, exposing neighbors and utility workers to the high voltage, even after workers have pulled the fuses to shut power off.
Following Hurricane Ivan, a utility lineman was working on a section of the heavily damaged utility lines. Workers pulled the fuses and checked the downed lines checked for voltage. After hours of work restoring lines in a neighborhood, a homeowner started a generator connected to backfeed his home and the lineman was electrocuted. Efforts at the hospital failed, and the lineman died.
Fire Hazard: Overloaded wires get hot. Without the protection provided by the circuit breaker inside the home’s electrical panel, wires may get hot enough to start a fire. A homemade cord with a 30-amp plug on one end used to backfeed a 15-amp circuit could allow double the current on the wires, causing significant overheating. Even if the home’s breaker did trip, all the other outlets on the circuit are still live.
Damage to Appliances: The issue with making a 120-volt connection between the generator and a regular 120-volt circuit in the house is that the home’s circuit breaker panel will distribute that power to every circuit on that leg of the panel. Panels have two sides, each 120 volts. 240 Volt circuits use both sides. Any 240-volt appliance will only receive half the voltage it needs. Under voltage could damage some appliances.
Potential Legal and Financial Repercussions: Backfeeding is illegal in many jurisdictions because of the inherent risks. Engaging in this practice can lead to hefty fines or potential legal action, especially if it results in harm to utility workers or neighbors.
The National Electrical Code states that connections must have built-in protection against returning current to the distribution network. Further, the code specifies that electrical cords may expose no one to electrical current—the male-to-male extension cords allow this to happen and are therefore illegal.
Generator Damage: Backfeeding can damage the generator. When the utility restores power, the generator and the utility will not be in sync. Because the utility can supply much more power, the generator will sustain significant damage and could injure anyone nearby.
According to Norwall PowerSystems, Backfeeding is a Dangerous Practice to Avoid.
Generator Extension Cords
30-Amp Generator Cord (upper left) 30-amp 4-outlet extension cord (right) 50-amp generator cord (bottom)
Another method uses heavy-duty outdoor-rated extension cords between the generator and each appliance. This is less ideal than the single generator extension cord. Provided the extension cords have a current rating that matches or exceeds the generator outlet circuit breaker rating, the connection is safe from overloads. Multiple extension cords increase the risk of tripping.
Transfer Switch: A Safe Alternative to Backfeeding Your House
Generac HomeLink 50-Amp Manual Transfer Switch—Safe, Fast, Easy, Reliable Generator-Home Connection.
An inlet box on the outside of the house connects to the transfer switch inside. A generator cord plugs into a 120/240-Volt outlet on the generator, and into the inlet box. The circuit breakers inside the transfer switch distribute power to the circuits they protect.
Using a transfer switch:
- Safeguards utility workers and neighbors.
- Protects the home’s electrical system from overloads.
- Ensures safe and easy connection between the generator and home.
- Delivers power to hard-wired appliances like the furnace and air conditioner.
The Interlock Kit
(Image rotated for clarity) Note the Metal plate that locks the double-pole 30-amp breaker in the off position unless the 200-amp main is in the OFF position.
- An interlock can provide power to the entire circuit breaker panel.
- The user must understand the generator power capacity and select only those circuits that need power AND are within the generator’s power capacity.
The interlock kit includes a double-pole breaker designed to fit in the main circuit-breaker panel. A generator inlet box wires directly to the double-pole breaker.
Usually, the interlock breaker is in the OFF position. A mechanical interlock prevents it from moving to the ON position unless the panel’s main breaker is OFF. This satisfies the NEC code requirement for built-in protection against feeding current to the grid.
When the homeowner wants to use the generator, they turn all the breakers in the panel to the off position, including the main circuit breaker. After the generator is running and connected to the inlet box, the homeowner moves the interlock breaker to the ON position (the Main must be in the OFF position for this to happen) and then adds one circuit at a time. The first loads to add are heavy loads like an air conditioner.
Bottom Line: How to Backfeed Your Home with a Generator
Backfeeding your home with a generator is dangerous to you, your family, your property, neighbors, and utility line workers. Despite arguments that one must only “follow the correct procedure,” the system has no built-in protections against many hazards.
No one should backfeed their home with a generator under any circumstances. Ever.
A Manual Transfer Switch offers the safest, easiest connection to your portable generator that allows your hard-wired appliances like the furnace and air conditioner to function, along with the other most important circuits that you might need.
An interlock kit provides a few more options with similar safety, but the operator must understand how to balance the generator load and only add circuits deemed necessary at that time.
For most homeowners, a manual transfer switch offers the safest, easiest options while meeting code requirements.
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About MJ Logan
MJ Logan began his writing career in third grade creating small booklets with a construction paper cover and two or three sheets of white typing paper, carefully folded in half and glued to the construction paper. His career led from electrical engineering and electronic test to network management, independent software development, and finally back to writing.
