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Generator Transfer Switch Using Circuit Breakers


By Dave Rongey - Summary:

How to Install a Circuit Breaker Interlock Kit for a Generator Transfer Switch: How a Circuit Breaker Interlock Kit Works, Selecting a Generator Interlock Kit.


Guide to Using an Interlock for a Generator Transfer Switch

Electrical Question: Is it possible to run electricity backwards through a circuit breaker?

  • I want to connect my generator to my House panel during a power outage.
  • I have a meter with a 200 amp main breaker which also has a panel for breakers.
  • I want to use the 50 amp garage breaker in this panel as a source from my generator to my house.

My plan for an outage would be to trip the main breaker and plug a home made cord into my generator and garage outlet.
Please advise, Thanks.

This electrical wiring question came from: Colin, a Homeowner from Fruit Heights, Utah.

Dave’s Reply:
Thanks for your generator question Colin.
Yes Colin, a typical circuit breaker works the same way protecting the circuit in both directions.

Generator Transfer Switch Circuit Breaker Interlock

Preparations for Installing a Circuit Breaker Interlock Generator Transfer Switch

  • Skill Level: Advanced – Best installed by a Licensed Electrical Contractor.
  • Tools Required: Electricians pouch of hand tools and the various power tools necessary for installing the generator and transfer switch or circuit breaker interlock kit.
  • Estimated Time: Depends on the type and size of the generator and transfer switch and the available access to the project area.
  • Important: Installing a generator and transfer switch must be well thought out and performed with a permit with all work being inspected.

How to Install a Circuit Breaker Interlock Kit for a Generator Transfer Switch

PLEASE READ THIS CAREFULLY!

  • The following information is to be used for a Main Electrical Panel ONLY.
  • This cannot be done from a Sub Panel
  • The Circuit Breaker Interlock can only be used at the Main Panel.

How a Circuit Breaker Interlock Kit Works

The photo above is from a job site where I installed a Circuit Breaker Generator Transfer Interlock device which allows either the main electrical panel breaker or the generator feed circuit breaker to be on, but never both. The interlock kit must be properly installed with the appropriate circuit breakers and then may only be used with the panel cover positioned and securely mounted in place. Consult the installation instructions of the specific interlock kit that is obtained.

  • Selecting a Generator Interlock Kit
    • This serves as a required Generator Transfer Switch and is listed with UL.
    • The circuit breaker for the generator power must be sized for the capacity of the generator, or match the circuit breaker that is on the generator, (consult your generator manufacturer specifications.).
  • Avoiding Generator Overload
    • This set up works well, but keep in mind that you may need to turn off some circuits to avoid overloading the generator and or causing a voltage drop condition.
    • We found this to be the case if our refrigerator and septic pump came on at the same time, so I had to turn off the breaker for the septic pump and run it later.
  • Generator Transfer Switch Required by Electrical Codes

    • IMPORTANT: A transfer switch or mechanical device such as the one shown in the picture must be installed to provide separation between the electric utility power and the generator power to prevent hazardous electrical conditions and to be compliant with electrical codes.
    • The home electrical panel circuit breaker for the generator feed must be sized to the capacity of the generator.
  • Sizing the Interlock Transfer Switch
    • The amount of power available to the home will be limited to the Size and Type of generator that you have.
    • Not all generators have the same design features such as voltage regulation.
    • The circuit breaker interlock kits for generator transfer switches are available for a variety of electrical panels, circuit breaker sizes and styles.
    • All home electrical generator systems and transfer switches must be installed with a permit and be inspected as per your local building department or jurisdiction.

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6 Responses to “Generator Transfer Switch Using Circuit Breakers”
  1. Levi Joseph Uri says:

    I just want to ask about power standby for our house using solar power. Can you send me a simple circuit and contactor or any relay which I can use for installation. Can you send me a circuit diagram?
    Thank you very much.
    Regards,
    Levi

    • Dave Rongey says:

      Hi Levi,
      There are some wiring diagrams that may be helpful for you, which are found here in the website in the Home Generator area, and the Solar Power area.
      I hope you find them useful for your application!
      Dave

  2. Linda says:

    We have a main panel in the basement and a subpanel in the garage – they are very far apart (3500 sq. foot house). We are getting a 7500 Generac generator. About half the circuits we want to power with the generator are powered by the subpanel in the garage (kitchen outlets and lights, 1 bedroom). However, half the circuits run through the basement main panel (2nd bedroom lights, living room outlets, furnace).

    How do we safely connect the generator to run selected circuits on BOTH panels? If we use a transfer switch for safety, would we need to buy 2 transfer switches (one for each panel)? This would add a few $100 to our cost. We’d also prefer not running 100’s of feet of extension cords to both panels.

    Appreciate any suggestions that will be safe and economical. Thanks.

    • Dave Rongey says:

      Hi Linda,
      Here are some thoughts about your 7500 watt generator set up and supplying essential circuits with standby power.
      There are a few ways to provide generator power for two panels and their circuits if there will be manual control or intervention, starting with positioning the generator transfer switch in an approved location by the main panel which can then provide power to a separate panel in the basement for essential circuits only, and this panel can be sized large enough to feed the garage panel where non-essential circuits may be identified and shut OFF during generator operation. However if this is to be a fully automated system then splitting up essential circuits from non-essential circuits into separate panels which are fed from an automatic transfer switch will be required. It is also possible to install two transfer switches, one at each panel location, however this will require an additional feed from the generator line to the garage panel location. All of this will need to be configured by taking the existing electrical service and circuit panels into consideration, and the possibility of installing a circuit breaker interlock.
      I should also add that I do not advise using or installing extension cords to be used with a generator system such as this. If this were a small generator powering a garage refrigerator or single device then using an appropriately size extension cord is OK for temporary power only.
      Dave

  3. Stephen Mulenga says:

    Thanks,

    You have sent to me the most needs in my electrical work making it easier!

    Many thanks.


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Generator Transfer Switch Using Circuit Breakers


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