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Generator Wiring Diagram and Electrical Schematics

Generator Wiring Diagram and Electrical Schematics: A generator is a core component of many people’s emergency preparedness plans. (Maybe you have a cool charcoal powered or a multi-fuel generator.) However many fail to think through how exactly they will power the items they want to run when the grid is down.

Generator Wiring Diagram and Electrical Schematics

Generator Wiring Diagram and Electrical Schematics

Generator Wiring Diagram and Electrical Schematics:

A generator transfer switch is a legal and proper way to power your home with an emergency generator. There are three main types: automatic, manual transfer sub panel, and a breaker interlock. Each has varying degrees of complexity, benefits, and expense.

Automatic transfer switches will sense a power loss, start your standby generator and automatically move your load to the generator. These are awesome – but very expensive and require a full-time dedicated standby generator.

Manual transfer sub panel switches are a good option. They are less expensive than automatic transfer switches (Starting around $300) and can be used with a portable generator. They typically only cover a few breakers which was problematic for me.

Breaker Interlock is the option I chose. It is National Electric Code compliant and is, in my opinion, the least expensive and most flexible option. My setup cost was just under $150. In this setup, you use a breaker to energize your existing breaker box. Switching it on is easy and safe. My wife did an unassisted dry run in under 5 min – which included getting the generator out of the building.

The breaker interlock system has come in very handy for us. We can turn on overhead lights, wash clothes and keep our food cold, charge our phones, run the internet, and much more….all while keeping our doors and windows closed and not tripping on extension cords!

Generator Wiring Diagram and Electrical Schematics Disclaimer:

I am not an electrician. After much consulting and oversight from a licensed 25-year Master Electrician, I believe these instructions to be correct and accurate for my jurisdiction. Electrical codes vary from place to place. In my place of residence, homeowners are allowed to do their own electrical work if it is up to code. You are responsible for any code violations, permits or awesome good stuff that comes from doing a project like this.


Generator Wiring Diagram and Electrical Schematics 1

I’ve listened to and have even seen people using a double male plug to energize their house during a power outage. This is dangerous.

  • It is an electrical code violation.
  • It is illegal in most places.
  • It is a fire hazard. The power created by your generator is generally greater than the rating for the receptacle, wire, and breaker.
  • If you don’t disconnect your main breaker it can shock the power company linemen – and you will get sued.
  • You can easily get shocked because the male plug prongs are exposed.

Step 2: Determine Your Generator Plug Type and Amperage

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First you have to figure out what type of amperage and plug type we are working with. You only want to do this on a generator with a big round plug. This will provide 220V (in the US) and power both sides of your breaker box. You will see the amperage written near the plug. Mine is a 30 Amp L-14-30.

For your convenience these are the most common sizes:

  • Nema L14-20 – 20 amp
  • Nema L14-30 – 30 amp
  • Nema CS6365 – 50 amp

Step 3: Supplies

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Generator Wiring Diagram and Electrical Schematics 3.1
Generator Wiring Diagram and Electrical Schematics 3.2

Gather your supplies.
For the sake of this build, we are going to assume you have a 30 amp plug on your generator – like the one shown. If you have one different please adjust your supplies.

Breaker interlock kit. Buy a UL-rated device that fits your specific breaker box. These have been tested and validated to work. Many insurance companies and jurisdictions require the UL rating.

30 Amp 2 pole (double) breaker. Again you will need to buy one that fits your breaker box. All breakers are not the same.

Wire. I bought 10 feet of 10 gauge wire in black, red, green, and white.

30 Amp power Inlet box.

Schedule 40 electrical conduit and fittings

Conduit body

Conduit glue

Flexible Non-Metallic Conduit and fittings (optional)

30 Amp generator extension cord. (Search Amazon for (your plug type) extension cord.)

Notice how all the amperage match. If you are using a 50 output on your generator you will need a 50 amp breaker, 50 amp power inlet box, a 50 amp extension cable and 8 gauge wire.

Step 4: Drill (or Find) Access Hole

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Measure 5 times drill once.
My house had a conduit old hole in the foundation. Most people will need to drill one. A hammer drill is extremely helpful in making one. Try to get the conduit hole as close to the panel as you can.

Step 5: Mount Power Inlet Box

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Remove the front cover from the power inlet box.
Remove a knockout and attach the PVC fitting. You can see here I opted for the watertight connector. Glue works just fine too.

Using tapcons mount the power inlet box to the wall.

Step 6: Test Fit and Glue Conduit

Use a hacksaw and cut the conduit to length.

Don’t glue it until you know it fits. Once you are good glue it down.

Step 7: Wire the Generator Inlet Plug

Once the glue is dry we can start to work on the wiring.

Remove the cover on the conduit body. Pull the wires through one at a time attaching them to the plug as you go along. Remove about 3/4 of an inch of the insulation. Use a large flat screwdriver or a nut driver to tighten the terminals.

Green – Ground to the power inlet box.
White – Common, W terminal
Black and Red – Load – either X or Y terminal.

Step 8: Push Wiring Inside

Push the wires through the conduit into the house one at a time.

Replace the conduit body cover, checking the proper fit of the gasket.

Fill any gaps between your conduit and the house with silicone or expanding foam.

Step 9: Prep Breaker Box for Wires

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Turn off all the branch breakers and the main power breaker.

Remove the front panel of the breaker box by taking out the four screws.

Remove one knockout and screw in conduit adapter or in my case a blue non-metallic conduit adapter.

Pull wires through conduit and into the box.

Step 10: Create Open Breaker Space

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The breaker interlock method requires the to most upper and right breaker space to be free.

Generally, you will need to move a breaker or two down. Most boxes will have enough spare wire to move things around a bit. If you do not have enough room and your breaker is 30 amps or less you can use a short piece of insulated wire and a wire nut.

DO NOT wire nut copper and aluminum wire together. They will corrode over time. You will need to pick up a wire splice at your local home store.

Step 11: Install Generator Breaker and Wires

Generator Wiring Diagram and Electrical Schematics 14

Install your new breaker in the freed-up space in the upper right of your breaker box.

The red wire goes to one terminal on the breaker and the black goes to the other.

The white wire goes to the common bond rail in the box.

The green wire goes to the ground rail.

Note: In a 2 wire home like mine – meaning no 3rd ground wire in the outlet box or the outlets in the home. It is acceptable in my jurisdiction to put the green ground wire to an open common terminal. It is not appropriate to use the ground wire for the common at the outlet.

Step 12: Install Breaker Retainer

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Now it is time to lock down that breaker from moving. Install the retaining bracket. My retaining bolt was located between the main breakers and the 30 amp breaker.

Step 13: Install InterLock on Panel Cover

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Flip the cover over and use the provided template.

Pre-drill the holes and then finish them out with the bit size noted in your instructions.

Turn the panel back over and install the sliding interlock bolts.

Reinstall the panel with all the breakers in the off position. With the main in the off position turn the generator breaker to the on position. Ensure the interlock allows for the on position. You may have to shift the position of the panel cover.

Turn the generator breaker to the off position and drop the slide so it can not be turned on. Ensure the Main can be turned to the on position. Adjust the panel cover if it will not.

If it does turn the breakers on one at a time – with a 5-second delay between breakers. This will distribute the start upload.

Attach decals included in your kit to your breaker box and the outside service box.

Step 14: Operation

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