What size generator for 200 amp service?
Not 48 kW. 200 amps at 240 volts is the panel's ceiling, not what the house draws; an actual load calculation on a typical 200 amp home lands at 15 to 25 kW. Example: a 2,500 sq ft 200 amp house with gas heat and a 3.5 ton AC calculates to about 14.9 kW here, a 18 kW standby, and 35.5 kW all-electric (past air-cooled sizes without load management).
Ceiling vs. demand at 200 amps
| Number | Watts | What it means |
|---|---|---|
| Service rating | 48,000 W | The most the panel may ever carry. Not a sizing input. |
| Example demand, gas appliances (2,500 sq ft, 3.5 ton AC) | 14,875 W | 18 kW standby |
| Example demand, all-electric | 35,475 W | 30 kW+ or load-managed |
| Essentials on a portable | ~2,000 W | 3,500W portable on an interlock |
Why the breaker label keeps fooling people
The main breaker is a limit, like a bridge's weight rating; driving a hatchback across doesn't require a 40-ton hatchback. Sizing rules live in NEC Article 220's load calculation, which counts the actual appliances at demand-adjusted values, and that's the number the whole-house calculator approximates. Salespeople occasionally quote the 48 kW ceiling with a straight face; the counter-question is "what did the load calc come to," and a good installer answers with a number in the teens or twenties, then talks about shedding the water heater to hit the class below.
Whole-panel transfer plus a right-sized generator plus load management is the modern pattern at either service size: the switch carries everything, the module sheds the tank heater or the AC for minutes at a time, and the generator stays a class or two smaller than the worst case. Capacity is the expensive way to solve a problem that scheduling solves free.
Questions people ask
What size generator do I need for 200 amp service?
Not 48 kW. The 200 amp rating is the panel's ceiling (200A x 240V = 48,000W), not your demand; a typical 200 amp house calculates out between 15 and 25 kW of actual load, which is why the 18 to 26 kW classes cover almost every 200 amp home, with load management pulling many down a size. Size to a load calculation, never to the main breaker.
Can a generator have a 200 amp transfer switch but fewer kW?
Yes, and almost all of them do. A 200 amp automatic transfer switch means the switch can carry the whole panel, so nothing needs rewiring; the generator behind it can be any size, with load-shedding modules keeping demand inside its rating. Whole-panel transfer with a 14 to 26 kW unit is the standard install, not a mismatch.
Will a portable generator do anything useful on a 200 amp panel?
The panel rating changes nothing about portables: a 7,500W unit on an interlock still carries the essentials list of any house (the fridge-furnace-sump math on our house pages). What it can't do is pretend to be the utility; you pick circuits. The service size only matters when someone tries to sell you 48 kW because the label said 200.