Jason Palmer, CPA, CITP

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Hurricane Tech – The Whole House Generator Option

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In my article, “Hurricane Tech – Keeping the Lights On with a Portable Generator”, I discuss the benefits and basics of having a Generator to keep critical devices such as Refrigerators, Freezers, Heating, and Communications operational in the case of a Utility Power Outage.  The limitation is that a Portable Generator can only provide electricity to a limited number of devices such as those mentioned above.

If you want the ability to power most every device in your home – as if Utility Power were still present – you need a Whole House Generator that is able to produce a similar number of Amps.  The average home with a 100amp electrical panel would require a Generator capable of producing approximately 12,000watts.  And, with a 200amp panel, the Generator would need to produce approximately 20,000watts.

It is possible to power an entire home with a Generator producing less than the above approximate output wattage ratings if using a “Load Shedding Generator Switch.”  (See my article “Hurricane Tech – The Load Shedding Generator Switch” for an explanation of how this can be accomplished.)

It is more common to use a properly sized Whole House Generator so that the average load on the Generator is between 50% and 70% of rated capacity.  If you have 200amp service and a 20,000watt Whole House Generator, and assuming normal living patterns so that only selected lights and appliances are in use at any one time, the Generator should be operating in that range.  Rarely are Electrical Circuits in any home at capacity but more likely at a similar 50% to 75% of maximum capacity.

The Whole House Generator is usually connected to the Main Electrical Panel of the home using an Automatic “Utility/Generator Transfer Switch” which works with the Generator to sense loss of Utility Power, Turn-On the Generator, and then switch the Power Source of the Electrical Panel to the Generator from Utility Power.  (See my article, “Hurricane Tech – The Utility/Generator Transfer Switch”.)

Other than following local Electrical and Plumbing codes and using Licensed professionals for the installation, the other major decision after the sizing capacity is the Fuel Source for the Whole House Generator.  The most popular use Natural Gas (NG), Liquid Propane (LP), while some use Diesel Fuel or Fuel Oil.  The actual output of a Generator can be affected by the Fuel selection.  NG/LP rated Generators will produce approximately 10% less output with NG.  With LP, the output is closer to the actual rating.  A 20,000watt Generator may actually produce 19,500watts with LP but only 17,280watts with NG

A Whole House Generator requires periodic testing/”exercising” and maintenance.  Typically, a Whole House Generator will turn itself on once per week and “exercise” for approximately 20 minutes.  Like any other Engine, Oil needs to be changed.  For most Whole House Generators this is approximately every 100 hours or annually depending on usage.  IT IS CRITICAL TO FOLLOW ALL MANUFACTURERS MAINTENANCE RECOMMENDATIONS.  Failure to do so may cause the Generator to fail or not to start when it is needed most during a Power Outage.

IMPORTANT SAFETY NOTE:  CONSULT WITH A LICENSED ELECTRICIAN AND GENERATOR PROFESSIONAL TO CONFIGURE AND SELECT A PROPERLY SIZED WHOLE HOUSE GENERATOR SUITABLE FOR YOUR NEEDS.  ALWAYS USE A LICENSED ELECTRICIAN AND LICENSED PLUMBER TO PERFORM THE INSTALLATION.  FAILURE TO INSTALL A GENERATOR, TRANSFER SWITCH, NATURAL GAS OR LIQUID PROPANE CONNECTIONS CORRECTLY MAY RESULT IN FIRE, EXPLOSION, SERIOUS INJURY, OR DEATH.

Hurricane Tech – The Load Shedding Generator Transfer Switch

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A Load Shedding Generator Transfer Switch allows you to do more with less.

A standard Generator Transfer Switch provides a one to one relationship for the Main Electrical Panel Circuit being protected by the Generator.  (To learn more about the technology, read my article, “Hurricane Tech – The Utility/Generator Transfer Switch”)

A Load Shedding Generator Switch assumes that the demand by protected circuits is less than the maximum potential load thereby allowing more Circuits to be protected.  It does this by splitting the Circuits in to two or more groups of Critical/Priority Circuits and Non-Critical/Secondary Circuits.   Under normal operating conditions, assuming total sustained operating load is within the capacity output rating of the Generator (i.e. the Generator is producing enough electricity to power all of the devices presently turned “On”), all Primary and Secondary Circuits receive electricity from the Generator.

When a Primary Circuit demands additional electricity, such as when Heating System circulator pump or fan turns on, the draw of electricity may be greater than that being produced by the Generator.  To mitigate the problem, the Load Shedding Generator Transfer Switch will automatically “Shed the Load” or shut-down Secondary, Non-Critical Circuits such as lights or perhaps another high wattage appliance like a dishwasher to re-balance the available electricity from the Generator and provide it to the Primary, Critical Circuits.

Here is why it works:  The average electrical circuit in a home is rated at a maximum of 15 amps.  But rarely does the actual sustained load, (the amount of electricity required by the plugged in devices while “On”), approach the rated maximum of 15 amps.   And certainly the surge load, (additional electricity that is required when a device is turned “On”), does not exceed it.  If either the sustained or surge turn-on load exceeded the rated 15 amps, the Circuit Breaker would be tripping to “Off” frequently.  When this does happen, you remove devices, (un-plug them), such as that 1000 watt Hair Dryer and you “shed load” by turning off other devices on the same Circuit until the Circuit Breaker stops tripping to “Off.”

The same exact principle and math apply to the Main Electrical Panel in your home or office, which is usually rated at 100amps or 200amps.   As noted above, an individual Circuit Breaker may trip.  But rarely does anyone have a Main 100amp or 200amp Breaker trip (to “Off”) because the whole house load requirement, (total amount of electricity in use), never gets close to the maximum rating.

The Load Shedding Generator Switch takes advantage of this principle by allocating the total amount of electricity being produced by the Generator to all connected Circuits on a Priority basis determined by Critical and Non-Critical Groups of Circuits.  Instead of you having to be explicitly mindful of which devices are “On” or “Off” and personally managing the available electricity from the Generator, the Load Shedding Generator Transfer Switch can do it for you.

NOTE:  Keep in mind that unless you have a Generator capable of powering your entire home or office, one where the Generator output capacity closely matches the rating of the Main Electrical Panel at 100amps or 200amps, that the primary purpose of Emergency Generator Power is for Life Safety and Critical Services.  Non-Critical Circuits and Devices will need to be managed or remain “Off” during the Power Outage.

With a standard Generator Transfer Switch, the Emergency Load Demand, (amount of electricity and Amps) required to run these critical Circuits will be determined in advance and is fixed.  The same is basically true for a Load Shedding Generator Transfer Switch except that you have the added benefit of adding and allocating power Non-Critical Circuits – if excess Generator power is available.

Put simply, I definitely want my Living Room TV, FiOS Router, Set-Top Box operational along with my Refrigerator, Freezer, Heating System, and Electronic Start Gas Oven as a “Critical Circuits.”  If after all other Critical Circuit Loads are met, there is excess Generator capacity available, I would like to be able to power up the TV and related electronics in the Master Bedroom.  But as soon as a Critical Circuit needs more power (like when the Circulator Pumps to the Heating System kick “On”), it is O.K. for the Load Shedding Generator Transfer Switch to cut power to the Master Bedroom TV to meet the demand and allocate the available Generator Power to the Heating System.

As a reminder, when running on Generator “Emergency Power”, you should be mindful of what devices are “On” or “Off” at all times.  If you do not have the Generator capacity to “light up the entire house like Times Square” then you need to manage the available capacity either manually or with a Load Shedding Generator Transfer Switch.

IMPORTANT SAFETY NOTE:  It is CRITICAL to consult with a Licensed Electrician to determine the proper device and appliance load demand along with Circuit ratings and configuration.  A Transfer Switch is connected to LIVE ELECTRICTY provided from either Utility Power or a Generator.  FAILURE TO FOLLOW MANUFACTURES INSTALLATION INSTRUCTIONS AND MAXIMUM LOAD RATINGS MAY RESULT IN FIRE, SERIOUS INJURY, SEVERE ELECTRICAL SHOCK, OR DEATH.

Hurricane Tech – The Utility/Generator Transfer Switch

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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.