A load shedding module is the piece of equipment that makes whole-house backup affordable. Rather than sizing a generator for every load a household could possibly turn on simultaneously, the module watches demand and disconnects designated large loads when the generator approaches its limit, restoring them when capacity frees up. The result behaves like whole-house backup without paying for whole-house capacity.
What the module actually senses and does
Most systems measure current on the generator output, or receive a load signal from the transfer switch controller, and compare it against a threshold. When measured demand rises past the threshold, the module opens a relay or contactor in the circuit feeding a designated load, typically an air conditioner, an electric water heater, a range, a dryer or a heat pump. When demand falls and stays down for a set interval, the load is restored. The delays in both directions matter: an immediate restore would cause a load to cycle rapidly, and an immediate shed would react to a harmless momentary surge. Better systems support multiple loads with a priority order, so the least important is shed first.
Air conditioning gets special treatment
Compressor loads are the usual target, and they get particular handling because a compressor must not be restarted immediately after being shed. A dedicated air conditioning shed relay interrupts the thermostat signal rather than the power to the unit, letting the equipment’s own anti-short-cycle timer manage the restart. Some systems can shed a second compressor before the first, allowing partial cooling rather than none. Interrupting the compressor while allowing the indoor blower to continue keeps air moving and avoids a frozen coil. These details are why manufacturers publish specific wiring arrangements for air conditioning rather than treating it as another circuit.
How this compares with a critical-loads panel
A critical-loads subpanel solves the same problem by construction: the large loads are simply never energized during an outage. Load shedding solves it dynamically, so those loads run whenever there is room. The dynamic approach is more pleasant to live with, since you may well get air conditioning in the evening when other demand is low, and it requires no rewiring of branch circuits into a new panel. It costs more in equipment and adds components that can fail. Many installations combine both ideas, transferring the whole panel and shedding the three or four largest loads, which is usually the cheapest route to a comfortable outage.
Where load shedding disappoints
The module only controls loads it is wired to control. A household that plugs in three space heaters during a winter outage can still overload a generator, because portable loads are invisible to the system. Shedding also does nothing about starting surges; a module reacts to sustained demand, not to the instantaneous inrush when a motor starts, so the generator still needs enough surge capability for the largest motor that remains connected. And a shed load is genuinely off, which can surprise someone waiting for hot water. Setting expectations with everyone in the house is part of commissioning the system. The other common gap is a load added after installation, such as an electric vehicle charger, which will happily consume the entire generator unless it is brought into the shedding scheme or locked out during outages.
Commissioning and testing it properly
A load shedding system is only trustworthy if it has been tested under realistic conditions, which means running the generator and deliberately adding load until shedding occurs, then removing load and confirming restoration. That test should be part of the installation and repeated occasionally, because thresholds can be set incorrectly and relays can fail. Document which loads are shed and in what order, and post that list with the transfer procedure. If you later add a large load, such as an electric vehicle charger or a heat pump water heater, revisit the configuration rather than assuming the system will cope. Capacity management only works when the configuration matches the house as it is today.
What to check before you act
- List the large loads and decide a shed priority order.
- Use a thermostat-interrupting relay for air conditioning, not a power cut.
- Test shedding and restoration under real load at commissioning.
- Revisit the configuration whenever a large load is added.
Common questions
Does load shedding replace sizing the generator properly?
No. It manages sustained demand but not starting surges, so the machine still needs surge capability for the largest motor that stays connected.
Will I notice loads being shed?
Usually as an appliance that stops for a while and resumes later. Documenting which loads participate prevents it from being mistaken for a fault.
The practical takeaway
Use load shedding to buy whole-house behavior from a mid-size generator, and configure the priority order deliberately rather than accepting defaults. Test shedding and restoration with real load before you rely on it, and post the list of managed loads where the household can see it. Then size the generator for surge, which shedding cannot help with.
References and further reading
- Department of Energy: appliance demand figures for setting shed priorities
- NFPA: National Electrical Code background on optional standby systems
- CPSC: generator capacity and home connection guidance
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
