Sizing guide
Load management, or just buy the bigger generator?
If the house's continuous load fits the generator and the trouble is several large loads starting at once, load management is the cheaper answer: a Cummins 20kW air-cooled unit manages up to four loads, enough for two air conditioners. Buy the bigger generator when the continuous load itself is too high.
The two questions people confuse
How much power does the house draw? is a steady-state question, and the answer is usually smaller than people expect. A large DFW home running two air conditioners, a refrigerator, lighting, networking and a pool pump is rarely pulling what its service size implies.
What happens when everything restarts at once? is a different question entirely. An air-conditioning compressor draws several times its running current for a fraction of a second at start. Two of them starting together is the single largest demand the house will ever place on a generator, and it lasts under a second.
Size for that instant with no management and you buy a machine that runs far below its rating for the rest of the outage.
What intelligent load management does
The control watches the generator's available capacity and restores large loads only when there is room. When the first compressor starts, the second is briefly held. When the first settles into its running current, the second is released. Both air conditioners run, started seconds apart instead of together.
The Cummins implementation on the air-cooled range:
| Property | What it means in practice |
|---|---|
| Control in the generator | The logic is built into the generator's controller. The loads are switched by the Cummins Load Add / Load Shed device (A051C329), which controls two 50 A loads. |
| Smart | Cummins says the generator continuously monitors how much power each load needs and restores only the loads it has capacity to run. |
| Responds to current | Cummins describes it as reacting to current demand rather than to engine frequency, which can only fall after the engine has started to slow. |
| Up to four managed loads | Typically two AC compressors plus two of: range, pool pump, well pump, electric water heater. Two Load Add / Load Shed devices. |
What the choice actually costs
The decision usually presents itself at the top of the air-cooled range. A 20kW air-cooled unit with load management, against stepping into the liquid-cooled range at 25kW:
| Option | Equipment price |
|---|---|
| RS17A — 17kW air-cooled | $5,326.86 |
| RS20A — 20kW air-cooled | $5,925.25 |
| RS25 — 25kW liquid-cooled | $17,622.48 |
The equipment gap between the top air-cooled unit and the entry liquid-cooled unit is $11,697.23, and that is only the machine. Liquid-cooled units are heavier, need a larger pad and carry a 2-year base warranty against 5 years on the air-cooled range, so the installed difference is wider than the price table shows.
Against that, load management on the air-cooled range needs the Load Add / Load Shed devices and their wiring. A soft-start module on the largest compressor works on the same problem from the other end, by reducing the startup surge itself. Price both against the gap above.
We price the soft start and the load management configuration before recommending a larger generator.
When load management is the right answer
Two air-conditioning systems in a house whose continuous draw is comfortably inside the generator's rating. This is the common two-story case, and the one load management is built for.
A single large compressor plus one other heavy intermittent load — a pool pump, a well, an electric range. These never actually need to run in the same second.
Any house where the sizing calculation lands just over a size boundary because of startup surge rather than running load.
When it is not
When the continuous load is too high. Load management sequences starts. It does not manufacture capacity. If the house needs more watts than the machine makes, all you get is a generator that shuffles loads for the whole outage.
When more than four loads need managing. Four is the limit on the air-cooled range. A house with three AC zones, a pool, a well and an electric range has exceeded it.
When nothing may ever drop. A home office with equipment that cannot tolerate being held back, medical equipment, a server rack. If a load must be continuously available, it should not be one of the managed ones — and if there are several of those, size for them.
When you want every load available at once. Say so and we will size for it. It costs more, and it should be a deliberate choice.
How to settle it for your house
Start with the sizing calculator, which gives you a range without asking for a phone number. Then read will a generator run my air conditioner, because in Texas the compressors decide this.
The final answer comes from the survey, where we count the actual loads, read the actual nameplates, and check the gas supply that has to feed whatever we land on. It takes about forty-five minutes and it costs nothing.
Questions
What is intelligent load management on a generator?
A control that watches what the generator can supply and restores large loads only when there is capacity for them. Instead of every air conditioner, oven and pump starting at once when the generator picks up the house, they come back in order, so a smaller generator can cover a house that would otherwise need a larger one. On the Cummins air-cooled range the generator controls up to four loads, switched through the Cummins Load Add / Load Shed device (part A051C329), each of which handles two 50 A loads.
Is load management the same as a load-shed relay?
Not quite. A plain load-shed relay simply disconnects a chosen circuit whenever the generator runs — you lose that load for the whole outage. Intelligent load management restores it as soon as there is headroom, so you usually get everything, just not all in the same instant.
What does Cummins load management measure?
Cummins describes its system as responding to current (amperage) rather than to engine frequency. A control that reacts to frequency can only act once the engine has started to slow under load; one that reads current can act on the demand itself. Compare it against any other brand's own documentation rather than a dealer's summary, ours included.
How many loads can it manage?
The Cummins air-cooled units manage up to four loads. Typically that is two air-conditioning compressors and two of the following: an electric range, a pool pump, a well pump, or an electric water heater. Each Load Add / Load Shed device (A051C329) controls two 50 A loads, so four loads take two devices.
Is it ever the wrong answer?
Yes. If the house needs more continuous capacity than the generator has — as opposed to needing help with simultaneous startups — load management does not create power that is not there. It solves a start-up problem. It does not fix an undersized machine; a house that needs more than the generator makes will spend the outage rotating loads.
Load management behavior described here is from Cummins dealer documentation for the 13–20kW home standby range. Equipment prices are the published prices on this site and exclude installation.
Been quoted a bigger generator than you expected?
Bring the quote. If a soft start and load management cover it, that is what we will quote.