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.