How to Connect a Generator to Your House Without a Transfer Switch

Many homeowners think about how to use a generator when the power goes out at home. They invest in portable gasoline-powered generators to keep the lights on during an emergency. You can plug appliances and medical devices directly into your generator, but if you want to send power to your home’s electrical outlets, an intermediary device is a necessity. Although a transfer switch can safely tie a portable generator to your household wiring, a generator interlock kit is a less expensive option for connecting an external source of electricity to your household circuit breaker panel. This mechanical device minimizes the risk of fire, damage, and electric shock to your wiring, yourself, and other people.

Generating Power With a Portable Generator

Small gasoline-powered portable generators use an onboard alternator to convert mechanical energy to electricity. Duplex ground fault circuit interrupter (GFCI) outlets can supply 120 volts each while protecting the user from electric shocks. Other 120/240-volt outlets provide a connection to two 120-volt terminals, a neutral terminal, and a ground wire. To obtain the full 240 volts, both 120-volt terminals are used to connect the generator to a circuit breaker panel. This setup mimics your normal utility supply. If you connect your generator correctly, you can use it to power your home without needing to move your appliances.

Quite a few people put off installing a portable generator transfer switch because of the expense, only to have difficulty utilizing a standby power source when the need arises. If you have a small house and space outdoors, it may be enough for you to plug essential home appliances that use standard three-prong plugs directly into the generator’s outlets. Bypassing the utility grid in this way to directly supply power indoors has its own set of risks. Loose cables, plugs, exposed terminals, and live wires can cause serious injuries. If you do choose to draw power straight from your generator, use properly rated outdoor extension cords. Dedicate one cord to each appliance to prevent overloading the circuit, and secure your cords with properly rated conduit, shielding, or tape.

The Danger of Back-Feeding Electricity Through Wires

Transfer switches and generator interlock kits prevent homeowners from back-feeding electricity into the utility grid. Connecting your portable generator directly to your circuit panel is dangerous and often illegal. Normally, utility lines carry high-voltage electricity that passes through a transformer before reaching your home. The power is regulated to supply 110 or 120 volts at a maximum amperage of 15 or 20 amps or 240 volts at 30, 40, or 50 amps. Back-feeding power from a generator distributes electricity throughout your home’s electrical circuits, but it can also send electricity back through power lines to the utility grid if your main breaker is on.

Switching off the main breaker before connecting a generator to your house will prevent power from feeding utility lines, but the setup can be hazardous. If the breaker is inadvertently turned on, there are no safeguards against energizing utility lines or electrocuting people or pets in the home. The generator supplies electricity through two 120-volt lines. If the generator plug is pulled out of the outlet, anyone who comes into contact with the terminals will be shocked. If the main power comes back on, back-feeding electricity into a convenience outlet can overload your circuits, damage your electronics, and overheat wiring to create a fire hazard. If the power flows back into the utility grid, you could be criminally liable if linemen or workers are critically or fatally injured.

How to Hook up a Generator to Your House

Transfer Switches

A transfer switch is a separate breaker panel that you install next to your main breaker panel. When your electric service goes out, you plug your portable generator into an outdoor outlet that’s connected to a transfer switch inside the house. The switch feeds electricity into branch circuit breakers in the breaker panel and prevents it from flowing into any other circuits.

Generator Interlock Kits

You can also safely draw power through your home’s circuitry by using a generator interlock kit. This cost-effective, legal alternative to a transfer switch is a manual, mechanical device that is relatively less expensive to procure and install. The interlock is a metal or plastic guard or bracket that allows the generator to feed electricity into your home’s circuitry while keeping the main circuit breaker switched off. It covers your service panel to deactivate the main power supply while the generator is running, and it blocks the flow of power to and from utility lines when the generator is on.

Choose the interlock kit that is designed to work with your generator and electrical panel. Take note of the location of the main breaker. Determine if the breaker is centrally positioned or placed to the right or left of the other switches. Measure the distance between the main and branch breakers. Record the amperage of the main breaker and the orientation of the switch so you can match an interlock kit’s specifications. Some vendors can guide you through this process so that you’ll be confident in your choice. There are many different models of generator interlock kits, so be sure to carefully follow the manufacturer’s instructions when you install the interlock switch on your breaker box.

When you are ready to install your kit, disable your main circuit breaker or primary power source so you can safely connect your generator to the house without accidentally electrocuting yourself. The mainline from the utility pole usually attaches to a metal box on the side of your house. Find the box and shut off any breakers labeled “main.” If you’re unsure about which breakers supply power, turn off all the breakers.

Install the Inlet Box Outside Your Home

Before you install the interlock kit on your breaker panel cover, you need to install the power inlet box that feeds electricity from the generator into your home. The box contains a green ground wire that connects the inlet to the ground screw.

• Locate your breaker panel and decide where you will install your inlet box.
• Bore holes through your house and the back of the box so they will align when you mount the box to the outside of the house.
• The inlet box will connect your generator to a dedicated breaker in your circuit panel. Prepare to wire the inside of the inlet box with a 10/3-gauge electrical cable. Measure enough cable to connect the breaker panel to the inlet box. Allocate extra length to pass through and bend around wall studs or other materials, and leave about 6 inches of slack above the breaker.
• Remove the cover from the inlet box and pull the cable through the hole you made.
• Use a metal collar to secure the cable to the entry point inside the box, and then strip off a few inches of insulation from the cable. You will see four wires: an unshielded copper wire, a black wire, a red wire, and a white wire.
• Connect the copper wire to the ground screw, and then connect the white, red, and black wires to the outlets on the box cover. The red and black wires will feed electricity from the generator into the breaker. The neutral wire is white. The outlet should be marked to indicate where you should place each different colored wire, so make sure you position each wire correctly.
• Once the outlet is wired, reassemble the box for mounting. Feed the remaining shielded wire emerging from the box through the hole into the house, and then mount the inlet box to the exterior of the house.
• Locate the cable you fed into the house and attach it to the wall with a staple as directed by your local building code.
• Strip the insulation from the long tail of the cable so you can connect the individual wires to your breaker panel. Attach the ground and neutral wires to the bracket surrounding the breaker panel. Make sure you understand where to attach these wires and hire the help of a licensed electrician if the placement is not clearly indicated. Then, feed the red and black wires into the 30-amp breaker that will connect to your generator. Make sure all wires are tightly secured.

Install the Generator Interlock Kit

Now you are ready to install the interlock switch plate onto your breaker panel cover. Here is a general outline of the steps most installations follow:

• Read any documentation and gather any tools and safety equipment you may need to complete the installation.
• Switch off the main breaker.
• Carefully remove the breaker panel cover, which is typically fastened with Phillips or flat-head screws. Do not touch any bare wires.
• Place the panel cover face-down on your workbench, and then align the panel with the interlock kit. Mark the location of each screw, and then drill the holes into the interlock kit so it can be installed over the panel.
• Use screws to join the interlock kit to the panel.
• Reattach the modified panel cover to the breaker box.
• Once the panel cover is secure, you can switch on the main breaker if your electric utility service is functioning normally.
• If the power goes out, adjust the interlock switch plate to shut off the main breaker while switching on the generator breaker.
• Plug in your generator outside, at least 20 feet away from the inlet box, and start it.
• When the generator is safely providing electricity to connected panel breakers, you can draw power from wired outlets.
• Once the main power comes back online, power down the generator and slide the interlock back to its initial position to restore utility service.

The Necessity and Cost of a Generator Interlock Kit

It is imperative to take safety measures when working with electricity to protect you, your family members, and your home. Depending on the regulations in your area and your level of experience, you may need to hire a licensed electrician to verify that your generator interlock kit meets local building codes and is compatible with your electrical system. Expect to pay between $1,000 and $1,500 total for parts and labor.

Safely Power Your Home

In the face of unpredictable power outages, portable generators are becoming an essential appliance. Many homeowners appreciate the convenience and peace of mind a portable generator has to offer. Portable generators can power sump pumps to prevent basement flooding, prevent food from spoiling, keep the heat or air conditioning on, and keep power running to essential appliances and security systems. They can literally be lifesaving devices when they supply power to medical devices, and they are ideal for providing a consistent supply of electricity in remote areas.

Transfer switches and generator interlock kits are essential to the responsible operation of your portable generator. Happily, the generator interlock kit is a solution that can save money as it keeps your home up and running in every circumstance. We hope that you have found this article on how to hook up a portable generator to a house without a transfer switch helpful.