Hurricane Tech – The Utility/Generator Transfer Switch

An Extension cord is suitable for connecting the Generator to an individual device such as a TV set or major appliance but it limits you to devices that would normally be connected (plugged-in) to an electrical wall outlet.  If you want to connect a Generator to devices that are “hard-wired” to the Electrical Panel in your home or office, such as a Heating/Hot Water or Cooling System, or use the wiring in your home instead of Extension Cords, you need a “Utility/Generator Transfer Switch.”

This is a special type of electrical panel that has two inputs:  one for the normal electricity feed from the Power Company and one for the electricity feed from the Generator.  The output is a series of Circuit Breakers that replace the selected critical Circuits in the Main Electrical Panel that you want to provide Generator Power to in the event of a Utility outage.  Think the letter “Y”.  A Switch determines if Utility Power or the Generator is powering the Circuits.

Utility/Generator Transfer Switches come in two flavors:  Manual and Automatic.  As the names imply, the Manual Transfer Switch requires you to physically “Switch” the Power Source connection from the Utility Company to the Generator.  With an Automatic Transfer Switch, once the Transfer Switch senses a Loss of Electrical Power from the Utility, it waits approximately 30 seconds, and performs a series of tests to make sure there is a true “power outage” and it flips the Power Source from Utility Power to Generator Power.  (When power is restored from the Utility Company, you guessed it, with a Manual Switch you have to flip it back yourself while an Automatic Switch figures out the Utility Power is back and seamless flips the Switch for you along with powering down the Generator.)

An Automatic Transfer Switch only makes sense if you have an Electric Start Portable Generator or Whole House Generator that can be started “Automatically” upon sensing loss of Power from the Utility AND if the Automatic Transfer Switch is COMPATIBLE with the particular Generator configuration you have installed.

The amount of Generator Power you have available – Portable (usually under 8,500 watts) or Whole House (usually 15,000 to 20,000 watts), will determine the number of Circuits the Transfer Switch will support.   A Utility/Generator Transfer Switch for a Portable Generator will usually have a four to six circuits.

For a Whole House Generator, there may be almost as many circuits as on a regular electrical panel.  This will usually be ten or more Circuit’s.  When a Whole House Generator has sufficient capacity to power every device in the home or office, there may be a Single 100amp or 200amp Circuit Breaker which will exactly match the capacity of the Main Electrical Panel.

The Fuzzy Math Example:  A Portable Generator which produces approximate 8,500 Surge Watts at 120v Output will provide approximately 70 amps of “surge/start-up” power and 45 amps of sustained “full load” power.  A Utility/Generator Transfer Switch that has four 15amp Circuits which is a maximum load of 60amps is the proper size for the Portable Generator in this example.

IMPORTANT SAFETY NOTE:  Check with a LICENSED ELECTRICIAN for proper sizing and installation of any Utility/Generator Transfer Switch.  Failure to follow proper installation instructions may result in serious injury or death.  A Utility/Generator Transfer Switch is being connected to LIVE 120 volt ELECTICIAL POWER.  Use a professional, licensed electrician, preferably one with an explicit knowledge of Generator Power Systems to perform the work.

You are probably wondering, “I have way more than four circuits in my home.  What is the point of a Utility/Generator Transfer Switch that only supports four circuits?”

Answer:  Remember in the case of MOST Portable Generators and even a smaller Whole House Generators (Sub 15,000 watts), the purpose is to provide EMERGENCY and LIFE SAFETY power to CRITICAL Circuits in the home or office.  This would include the Refrigerator, Freezer, Heating System, Communications (TV, Internet, Phone), some Lighting and perhaps the Electric Ignition Starters for your Gas Oven, Stove, or Hot Water Heater and other critical Electrical Appliances.

To that end, the Circuit Breakers in the Utility/Generator Transfer Switch REPLACE the equivalent ones in the Main Electrical Panel.  When Utility Power is present, the Transfer Switch acts like a Sub-Electrical Panel.  The Circuits receive Utility Power exactly as if these Circuits were still in the Main Electrical Panel.

During a Power Outage, after the Power Source Switch is set to “Generator”, this entire Sub-Panel is COMPLETELY DISCONNECTED from the Utility Power and the power source is the Electricity from the Generator.

CRITICAL SAFETY NOTE:  The most important function of the Utility/Generator Transfer Switch is to connect EITHER UTILITY POWER OR GENERATOR POWER to the Circuits.  THE TRANSFER SWITCH ASSURES THAT ONLY ONE POWER SOURCE IS ACTIVE AT A TIME.  NEVER ATTEMPT TO BY-PASS THIS CRITICAL SAFETY FUNCTION.   Having both Utility Power AND Generator Power active on the same Circuit at the same time may result in Fire, Serious Injury, and Death.


  1. If you are Planning a Manual Transfer Switch Installation here is a good article to get you started

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