What a 30kW Generator Actually Powers
I've walked into too many small commercial jobs where the owner bought a 30kW unit because "the neighbor has one," and then watched it lug down every time the walk-in compressor kicked. Size the load first, buy second. A 30kW standby generator is a serious machine — at 240V single-phase it delivers 125 amps of continuous power, enough for most large homes, small restaurants, farm shops, and light commercial buildings. But the nameplate only tells half the story. Starting loads are where systems live or die.
Here is the honest math we run before we spec any unit in this class. Motor-driven equipment — air conditioners, refrigeration compressors, well pumps, air compressors — pulls three to six times its running current for the first few cycles. A 5-ton rooftop AC unit that sips 6,000 watts while running can demand 18,000 watts the instant the contactor slams shut. Stack two of those on a lazy sizing job and your 30kW machine is already in trouble before the first outage.
Typical Loads a 30kW Unit Handles
The table below uses field-measured values we see repeatedly on commercial and large-residential installs. Treat these as planning numbers, then verify against the nameplate of the actual equipment on site — a "5-ton" condenser from 1998 and a 2026 variable-speed unit are two very different animals.
| Load | Running Watts | Starting Watts (est.) | Notes |
|---|---|---|---|
| 5-ton central / rooftop AC | 6,000 | 15,000–18,000 | Largest single starting load in most buildings; soft-start kits cut surge 60–70% |
| Walk-in cooler compressor (2 HP) | 2,400 | 7,200 | Defrost heaters add 3–6 kW on a timer |
| Commercial electric range | 8,000–12,000 | same as running | Resistive, no inrush |
| 3 HP well pump (240V) | 2,800 | 8,500 | Check control box rating and pressure tank precharge |
| Commercial washer / dryer pair | 5,000 | 6,500 | Motor plus heat element |
| Office lighting + receptacles (per 5,000 sq ft) | 6,000–9,000 | same as running | LED retrofits cut this 40% or more |
| Electric water heater | 4,500 | same as running | Stagger elements if possible |
| Level 2 EV charger | 7,700–11,500 | same as running | Continuous load — derate per NEC 625 |
Add up the running watts of everything that must operate simultaneously, then add the single largest starting surge. If that number lands under 24,000 watts, a 30kW machine has healthy headroom — the rule we use in the field is keeping continuous load under 80% of rating so the engine isn't screaming at redline through a week-long outage. Engines that live at 95% load drink oil, run hot, and die young.
One more field note before we leave the load table: nameplate amps lie politely. We carry a clamp meter on every commissioning and we measure actual running current on each major circuit. On a winery job last fall the "6 kW" glycol chiller measured 8.9 kW at 208V because the pump package was specced separately. Measured beats printed, every time.
Amps, Voltage, and Wire: The NEC Side of a 30kW Install
We've pulled thousands of feet of copper for generator feeders, and the sizing questions are always the same. The table below converts 30kW into real amps at the voltages you'll actually encounter, using the basic power math — single-phase is watts divided by volts, and 3-phase divides by volts times the 1.732 root-three factor.
| System Voltage | Configuration | Full-Load Current | Application |
|---|---|---|---|
| 120/240V | Single-phase | 125 A | Homes, small offices, farm shops |
| 120/208V | 3-phase | 83 A | Small commercial, restaurants, retail |
| 277/480V | 3-phase | 36 A | Larger commercial with step-down transformation |
Now the part that fails inspections. NEC 445.13 requires generator feeder conductors to carry at least 115% of nameplate current unless the installation design limits loading, and NEC Article 702 governs the whole optional standby system — transfer equipment, signage, and the load calculations in 702.4. Since standby power is a continuous-duty application in practice, we size conductors at 125% and sleep better. Cross-reference our NEC compliance guide and the NEC wire sizing guide with ampacity charts before you pull a foot of wire.
| Generator Output | Design Current (×1.25) | Breaker (NEC 240.6) | Copper THHN/THWN-2 @ 75°C (310.16) | Aluminum @ 75°C |
|---|---|---|---|---|
| 125 A @ 240V 1φ | 156 A | 175 A | 2/0 AWG (175 A) | 4/0 AWG (180 A) |
| 83 A @ 208V 3φ | 104 A | 110 A | 2 AWG (115 A) | 1/0 AWG (120 A) |
| 36 A @ 480V 3φ | 45 A | 50 A | 8 AWG (50 A) | 6 AWG (50 A) |
Conduit fill matters here too — three 2/0 THHN conductors plus an equipment ground in one raceway needs 1-1/2" EMT at minimum, and my crews go 2" on any run with more than two bends because pulling tension ruins more insulation than bad math ever did. Check the conduit fill chart and the wire ampacity chart against your actual run length, ambient temperature, and bundling conditions. Long feeders also deserve a voltage-drop check: keep it under 3% and upsize one gauge on anything past 150 feet.
Fuel Consumption: What a Week-Long Outage Really Costs
Fuel planning separates professionals from hopefuls. Liquid-cooled machines in the 30kW class on natural gas or propane burn serious volume at load, and the consumption curve is not linear — the last 25% of throttle costs a disproportionate share of fuel. The figures below are typical for the liquid-cooled 30kW class; confirm against the specific model's published fuel data sheet before you size tanks or gas service.
| Fuel | 50% Load (typical) | 100% Load (typical) | 24-Hour Burn @ 75% | Planning Note |
|---|---|---|---|---|
| Natural gas | ~280 ft³/hr | ~430 ft³/hr | ~8,600 ft³ | Confirm meter capacity; 30kW often needs a 2 PSI service or upsized meter |
| Liquid propane | ~3.1 gal/hr | ~4.7 gal/hr | ~94 gal | A 500-gal LP tank (400 usable) gives roughly 4 days at 75% load |
| Diesel (same class) | ~1.6 gal/hr | ~2.5 gal/hr | ~48 gal | Needs on-site storage and a fuel polishing schedule |
One detail that bites people every winter: propane tanks vaporize slower as they empty and as temperature drops. A 250-gallon tank in a January cold snap may not feed a 30kW unit at full load no matter what the gauge says, because liquid withdrawal outpaces vaporization and the regulator starves. We specify 500 gallons minimum for LP in cold climates, and we upsize first-stage regulators to match full-load demand at 0°F. On natural gas, have the utility confirm delivered pressure under system-wide peak demand — a neighborhood running every furnace at once during an ice storm is exactly when your generator needs full pressure.
Featured Unit: Briggs & Stratton 076880 Fortress 30kW
The Briggs & Stratton 076880 Fortress is the value pick we keep coming back to in this class. It runs a 1.6L 4-cycle industrial engine, delivers 120/240V single-phase power, and ships in a corrosion-resistant aluminum enclosure that holds up in coastal and snow-belt installs where painted steel rusts through in five years. The Fortress line's sound attenuation keeps neighborhood noise complaints down — meaningful when the machine sits 15 feet from a property line and runs for six days straight.
The InfoHub wireless monitoring lets an owner (or us, on a service contract) watch oil pressure, battery voltage, and exercise status from a phone — that alone has saved our customers a dozen service calls when the unit reported a weak battery weeks before an outage would have exposed it. A standby generator with a dead starting battery is a very expensive lawn ornament, and remote monitoring is how you catch it while it's still a $200 fix.
Briggs & Stratton's Symphony Choice power management deserves a paragraph of its own because it changes the sizing conversation. Instead of stalling under combined surges, Symphony sheds and re-sequences managed loads — you can run a larger effective load profile on the same 30kW machine. On retrofit jobs where the service entrance can't support a bigger feeder, that feature has saved entire projects. Pair the unit with a properly sized automatic transfer switch — for a 125A output, a 200A service-rated ATS from our 200–225A transfer switch range is the standard whole-building configuration, with the broader transfer switch catalog covering sub-panel and manual options for partial-backup jobs.
Five Factors That Decide Whether 30kW Is the Right Size
1. Honest load calculation
Run the NEC 220 or 702.4 math, or better, pull 12 months of utility interval data and look at the real peak. Guessing costs money in both directions — undersized machines stall, oversized machines wet-stack and wear out from light loading. Our generator sizing guide walks the full method, and the whole-house sizing article covers the residential version step by step.
2. Starting surge stack-up
One 5-ton AC starting is manageable. Two condensers plus a well pump hitting the same second is not. Load management modules or a soft-start retrofit on the biggest compressor usually cost a fraction of stepping up to a 38kW or 48kW machine, and they improve power quality for everything downstream.
3. Fuel availability at your site
Natural gas is effectively unlimited runtime but depends on utility pressure holding during disasters. Propane gives you independence with a hard runtime ceiling. Diesel stores longest but needs fuel polishing and tank maintenance. Pick for your worst realistic outage, not the average one — hurricanes and ice storms don't read averages.
4. Future load growth
EV chargers and heat pumps are landing on panels everywhere. If you're planning a Level 2 EV charger install or a heat-pump conversion in the next five years, size for it now. Swapping a generator later means a new feeder, a new ATS, a new pad, and a new permit — double the labor you already paid once.
5. Altitude and temperature derating
Engines lose roughly 3–4% of output per 1,000 feet above sea level, and hot ambient air costs additional output on many spec sheets. A 30kW unit installed at 6,000 feet in a warm climate is functionally a 24–25kW unit. We see this missed constantly on mountain and desert jobs, and it only surfaces during the first summer outage at full load.
How a 30kW Compares to Neighboring Sizes
Most buyers cross-shop three tiers. If 30kW is more machine than you need, the 22kW class covers most 2,500–4,000 sq ft homes with load management. If 30kW feels borderline, read the complete 26kW guide first — and if your load calculation honestly exceeds 26kW continuous, don't talk yourself into undersizing to save on the purchase price. For smaller applications, browse our 10–15kW range; for the featured Fortress line, see the Briggs & Stratton collection.
| Class | Best Fit | Typical Fuel | Cooling | Relative Installed Cost |
|---|---|---|---|---|
| 22–26kW | Large homes, small offices | NG / LP | Air-cooled | $$ |
| 30kW | Estates, restaurants, farm shops, small commercial | NG / LP / diesel | Liquid-cooled | $$$ |
| 38–48kW | Multi-tenant light commercial, large farms | NG / LP / diesel | Liquid-cooled | $$$$ |
Liquid cooling is the real dividing line, not the kilowatt number. Air-cooled engines are fine for the occasional multi-hour outage; a machine that must run five consecutive days at high load wants a radiator, a proper oil pump, and 1,800 RPM longevity. That's what you pay for in the 30kW class, and it's money well spent if your outages are measured in days.
Maintenance: The Schedule That Keeps It Alive
A 30kW generator is a small industrial engine that sits idle 95% of its life. That idle time is what kills them — stale fuel, flat batteries, condensation in the crankcase, and wasp nests in the air intake (yes, really, and more than once). The schedule we put customers on: weekly automatic exercise, monthly visual inspection, oil and filter every 100–200 run hours or annually, battery load-test every year with replacement around year three to four, and a full load-bank test every two to three years. Skip the load-bank test on a diesel and you'll find out about wet stacking during the outage, not before it.
Installation Essentials We Never Skip
Every 30kW install we sign off includes: a poured concrete pad or rated composite pad on compacted base; manufacturer-specified clearances with three feet minimum on service sides; gas line sized for the full BTU demand with a sediment trap; a service-rated ATS with a proper disconnect; and grounding per NEC 250 — two rods minimum unless a single rod proves 25 ohms or less, covered in our grounding and bonding guide. The generator gets its own disconnect means, and the transfer switch listing must match the application — service-entrance rated if it sits ahead of the main breaker.
Then we exercise-test under at least 50% load for two hours before calling the job done, because a machine that's never seen real load is an unproven machine. We log oil pressure, coolant temperature, and output voltage at no load, half load, and near-full load, and we hand the owner that sheet. It's the baseline every future service call gets compared against.
Common Mistakes We See on 30kW Jobs
After enough service calls, the patterns repeat. First, undersized gas piping: a 30kW unit at full load wants roughly 430,000 BTU/hr of natural gas, and the half-inch line that fed the old furnace won't carry it at pressure. We end up re-piping more often than not, and it's cheaper to do it at install than after a failed startup. Second, pads poured without checking frost depth — a pad that heaves two inches in February twists the enclosure, kinks the fuel flex line, and trips vibration sensors. Third, nobody exercising the block heater circuit; a cold-soaked engine at 5°F cranks slow, and slow cranking on a marginal battery is the number-one cause of failed starts we get dispatched on.
Fourth, and most expensive: buyers who size to today's load and ignore tomorrow's. The building that adds a second walk-in or an EV charger next year owns a generator that's suddenly too small, and the resale market for a used standby unit is brutal. Spend the extra capacity now or accept the replacement cost later.
Warranty and Service Reality
Standby generators in this class typically carry multi-year limited warranties on parts, with labor coverage that varies by brand and dealer network. Read the labor terms before you buy — a five-year parts warranty with one year of labor means you're paying a technician's hourly rate in year two for a covered part. Also confirm who services the unit locally. The best machine with no qualified tech within 100 miles is a liability during an extended outage. We stock parts for the lines we sell precisely because waiting ten days for a control board during a storm aftermath is not a service plan.
Register the warranty the day the unit is commissioned. We've seen owners lose coverage on a failed alternator because the registration card sat in a desk drawer past the deadline. It takes five minutes and it's the cheapest insurance on the whole project. Keep the commissioning sheet, the load test log, and the fuel receipts in the same folder — when a warranty claim lands, that paperwork is the difference between approval and a argument you won't win.
Ready for numbers on your building? Request a quote and we'll run the load calculation against the real equipment on your site — measured, not guessed.
Frequently Asked Questions
Will a 30kW generator run my whole house?
For most homes up to about 5,000 square feet with standard central air, yes — with room to spare. The limits appear with multiple large AC units, electric resistance heat, or on-demand electric water heating running simultaneously. Load management or a soft-start kit usually closes the gap without upsizing the generator.
How long can a 30kW generator run continuously?
Liquid-cooled natural gas units can run for weeks, limited by oil change intervals (typically every 100–200 hours under load) and utility gas pressure. Propane units run until the tank empties — plan on roughly four days at 75% load from a 500-gallon tank.
What size transfer switch does a 30kW generator need?
At 240V single-phase, 30kW is 125 amps, so a 200A service-rated automatic transfer switch is the standard whole-building choice. If you use a sub-panel ATS for selected circuits only, size it to the managed load, never below the generator's output feeding it.
Can I install a 30kW generator myself?
No — and the electrical isn't even the hardest part. Gas plumbing at this BTU rate, placing a machine over half a ton, NEC 702 transfer equipment rules, permitting, and warranty registration all require licensed trades. DIY attempts usually void the warranty and fail inspection.
How much does a 30kW generator cost installed?
Equipment in this class runs in the low-to-mid five figures depending on fuel type and enclosure options, and turnkey installation — pad, gas, electrical, ATS, permits — typically adds 40–70% on top. Complex gas service upgrades push it higher. A real quote requires a site visit.
Is 30kW enough for a small restaurant?
Usually, if the cooking line is gas-fired. All-electric kitchens with convection ovens, fryers, and walk-in refrigeration can exceed 30kW at full simultaneous load. Meter the building during a Friday dinner rush before deciding — that number settles the argument.
