Perkins Generator Guide: Choosing the Right kW/kVA for Your Facility (2025)

There's No One 'Right' Perkins Generator Size. Here's How to Find Yours.

I've been managing equipment budgets for the past several years. Over that time, I've tracked every generator purchase, replacement, and service contract for our facilities. One thing I can tell you: the question of "what size Perkins generator do I need" doesn't have a single answer. It depends entirely on your scenario.

From the outside, it looks like you just add up the loads and pick a generator. The reality is that load composition, start-up current, and even your facility's power factor change the math completely. People assume a 175 kW generator and a 1250 kVA generator serve different markets entirely. That's true—but the decision isn't always about raw power. Sometimes it's about redundancy, fuel flexibility, or future-proofing.

Let's break this down by the three most common scenarios I've encountered.

Scenario A: Standby / Emergency Power (50 kW – 200 kW range)

This is the most common scenario I see. A facility needs backup power for critical systems: lighting, HVAC for server rooms, maybe a few production lines. They don't need continuous run time—just enough to keep things going until grid power returns.

What I've found works best here is a Perkins 1100 series or 1200 series generator in the 50 kW to 175 kW range. The Perkins 1106A-70TG1 (175 kW standby) is a workhorse I've recommended several times. It's reliable, parts are widely available, and it doesn't overpower your budget.

But here's where I've seen people get tripped up: don't just add up your running loads. Motors, pumps, and compressors can draw 3–5 times their running current during start-up. If you size strictly to running load, your generator may stall the first time an HVAC compressor kicks on. I've seen this happen. It's not pretty.

For standby applications, I usually recommend a generator rated at 125%–150% of calculated running load, depending on motor content. A 175 kW Perkins industrial generator might be overkill for a 120 kW running load—until that 30 kW motor starts. Then it's just right.

Pro tip: Many vendors will quote a 150 kW generator for a 120 kW running load. I' ve learned to ask: "What's the largest motor start-up current?" If they can't answer, I get nervous. That quote might be too small.

Scenario B: Continuous / Prime Power (industrial, 200 kW – 1250 kVA range)

This is a different animal. If you're running a generator continuously—say, for a remote mining operation, a datacenter, or a manufacturing plant with unreliable grid power—you need a generator built for sustained output. That's where the larger Perkins 2500 series and 4000 series engines come in.

The 1250 kVA Perkins generator (typically with the Perkins 4006 or 4012 engine) is a beast. I've only had hands-on experience with one installation, but I consulted on another. Both were for facilities that couldn't afford any downtime. In those cases, the decision wasn't about cost per kW—it was about reliability and service support.

What surprised me is the maintenance difference. A standby generator might require an annual oil change and battery check. A prime power generator at 1250 kVA? That's oil and filter changes every 250–500 hours, plus coolant analysis, injector checks, and major overhauls at 10,000–15,000 hours. The ongoing cost is significant.

Honestly, I'm not sure why some vendors push a single size for continuous applications—maybe because it's cheaper for them to stock one model. My best guess is they're prioritizing inventory over fit. For continuous power, I've learned to look at load factor, duty cycle, and ambient temperature. A 1250 kVA generator at sea level in a temperate climate is different than the same unit at 3,000 meters in a hot environment.

If you're in this scenario, I strongly recommend getting a detailed load study done. It's worth the $2,000–$5,000 investment. I once skipped that step and ended up with an undersized unit. The derating curve was steeper than the vendor estimated. We had to upgrade within 18 months. That was a penny-wise, pound-foolish move I won't repeat.

Scenario C: Commercial / Mixed-Use with Dual Fuel or Special Requirements

This is where things get interesting. Some facilities don't need a dedicated diesel generator. Maybe you have natural gas available and want the option to switch. Or you're looking for a 9500 watt dual fuel generator for light commercial use—which is a very different product from the 1250 kVA industrial unit.

The 9500 watt dual fuel generator is an affordable, flexible option for small commercial backup or construction sites. I've used one for a warehouse that needed lighting and a few outlets during outages. It's not going to run a full production line, but it's better than nothing. And the dual fuel capability (gasoline or propane) gives you fuel flexibility during shortages.

But here's the catch: wiring it correctly matters. I've seen people try to connect these directly to a building's panel without a transfer switch. That's dangerous and often illegal. How to wire a fuel pump to a toggle switch is a common question I've encountered, and it's relevant here because the generator's fuel system (for the engine itself) needs proper wiring. A cheap toggle switch that can't handle the current will fail. I learned that one the hard way.

If you're using a battery charger for your generator—say, the Optima Battery Charger 1200—make sure it's compatible with your starting battery. I've seen installations where a charger was undersized, and the battery went dead between tests. That's a failure waiting to happen.

What the industry doesn't tell you: For dual fuel generators, the transition between fuels isn't always seamless. If you switch from propane to gasoline, the carburetor may need adjustment. It's not a set-and-forget system. Plan for a service call if you switch frequently.

How to Determine Which Scenario You're In

Still not sure? Ask yourself these questions:

• How often do I expect to run this generator? Less than 100 hours/year? You're Scenario A (standby). More than 1,000 hours/year? You're Scenario B (continuous). Somewhere in between? Scenario C or a hybrid.
• What's the largest single load? If it's a 200 hp motor, you need careful sizing. If it's a few lights and computers, you have more flexibility.
• Do I need fuel flexibility? If natural gas is cheap and available, a dual fuel option makes sense. If you need absolute reliability, diesel (Perkins) is hard to beat.
• What's my budget for ongoing maintenance? A 1250 kVA generator might have annual maintenance costs of $5,000–$15,000. A 175 kW standby unit might cost $1,000–$3,000 per year. Don't just look at the purchase price.

I've seen procurement managers buy a 1250 kVA generator because they thought "bigger is safer." That's not how it works. Oversizing is expensive—both upfront and in maintenance. Undersizing is dangerous. The right size is the one that matches your actual load profile and duty cycle.

If you're still unsure, get a load bank test done. It's the cheapest insurance you can buy. I've made mistakes in this area, and I'd rather you learn from mine than experience them yourself.

Prices as of April 2025; verify current rates with suppliers. Generator sizing calculations should be reviewed by a licensed electrical engineer.