SDMO Generator FAQ: 400 kVA vs 30 kW Diesel, Dual Fuel, and Inverter Generator Basics

I'm an office administrator, not an electrical engineer. That didn't stop our company from putting me in charge of backup power purchases. In the last few years, I've bought an SDMO generator twice: a 400 kVA SDMO generator for a warehouse, and a 30 kW SDMO diesel generator for a smaller office. This FAQ covers the things I wish I'd known before those purchases—whether you're considering a dual fuel natural gas generator, wondering what an inverter generator is, or just trying to figure out why one generator costs so much more than another.

The questions I hear most are about size, fuel type, and the costs that never show up on the first quote. Here's what came up for me.

Why buy an SDMO generator instead of a no-name brand?

Cheaper equipment looks tempting on paper. I get it. But an industrial generator isn't a portable appliance. Take the cheap route and you may save 15% upfront, then lose it all on service calls and compatibility headaches. We made that mistake with a non-SDMO unit years ago. It had enough power on paper but couldn't handle the starting surge of a chiller without flickering the whole building.

The SDMO line uses Kohler technology, which gave us consistent support across different sites. Their range is broad—roughly 20 to 1250 kVA—so if you have two very different locations, you can standardize on one brand. Is it the lowest price? No. Is it defensible when finance asks why you picked a recognized brand? Yes. That's not because the machines are the same under the skin; it's because the engineering and support behind them are different.

Do I need a 400 kVA SDMO generator or will 30 kW do?

Sizing is where buyers get into trouble. I don't have hard data on how often people oversize or undersize, but based on my own orders, it's pretty common. For a small office with basic lighting, computers, and a few mini-split systems, a 30 kW SDMO diesel generator is usually enough.

A 400 kVA SDMO generator is a different beast. That's about 320 kW at a standard 0.8 power factor, so it's meant for motor loads, larger HVAC, or production equipment with high starting surge. My rule of thumb: get your actual running load in kW, add 20-25% headroom, then think about motor starts. If you ignore the start surge, the generator can stall the second a large load kicks in. Worse than expected. It's a lesson I learned by watching an undersized unit struggle.

Should I choose a dual fuel natural gas generator instead of diesel?

I was curious about this myself. A dual fuel natural gas generator is attractive because natural gas is often cheaper and burns cleaner. And there are portable units like the Champion tri fuel inverter generator that run on gasoline, propane, and natural gas—handy for job sites or home backup.

But for a fixed industrial installation, I stayed with diesel. A diesel generator holds its own fuel, so we control the supply. A natural gas unit depends on the distribution network. In severe weather, gas pressure can drop right when you need it most. Dual fuel flexibility is real, but it also brings extra permits, gas piping, regulators, and more points of failure. We also looked at installation timelines. Natural gas piping can take weeks to arrange; a diesel tank is straightforward by comparison. Does that mean dual fuel is bad? No. It means you should understand what happens upstream of the generator before you commit.

What is an inverter generator, and do I need one for backup power?

This question always comes up after someone searches "what is an inverter generator" and finds a small portable unit online. An inverter generator converts the raw AC power to DC and back again, producing a clean, stable waveform. That's great for laptops, phones, and other sensitive gear. Some inverter generators are also quieter and lighter than standard units.

The Champion tri fuel inverter generator is a good example of what a portable, multi-fuel inverter unit can do. But it's not the same job as an industrial SDMO generator. A 400 kVA unit or a 30 kW SDMO diesel generator is built for whole-building loads, not just a few devices. If you only need to power some electronics after an outage, a small inverter generator may be all you need. If you're keeping a facility running, you need the bigger machine. There's a place for both; it's about matching the machine to the job.

How much maintenance does an industrial diesel generator actually need?

More than you want, less than you fear. Once the unit is installed, the big pieces are the engine, cooling system, battery, transfer switch, and alternator. We schedule periodic load tests and do a full inspection at least once a year.

The thing I'd want to tell another admin buyer: don't defer maintenance to save money. I did that once with an older generator, and it failed during a summer outage. The repair bill was several times the cost of the maintenance plan we'd skipped. Deferred maintenance savings are small; emergency repair costs are not. Some people say you can just change the oil and call it done—until the transfer switch fails and the building goes dark. That's a hard way to learn what that component actually does. Not ideal, but workable, if you schedule the work before you need it. For buildings with critical uptime needs, NFPA 110 provides a framework for emergency system performance. Most normal offices don't need hospital-level redundancy, but the discipline of regular testing is worth borrowing.

Where do hidden costs show up in a generator purchase?

The generator price is the shiny number everyone focuses on, but it's not the real price. You may need a concrete pad, an enclosure, an automatic transfer switch, fuel tank, exhaust, wiring, permits, and a way to get the unit into the building. For our 400 kVA unit, installation and site work outweighed the equipment cost. Even for the 30 kW unit, the extras were smaller but still caught me off guard.

I don't have a clean percentage to give you—it depends too much on location and local code. What I can say is: get a site-specific quote before setting your budget. Ask about delivery, lifting, and commissioning. Ask who handles the local permitting and inspections. When a quote looks too simple, ask for a full line item breakdown. That's when the real numbers come out. The vendor who can give you a realistic installed price is worth more than the one with the cheapest brochure.

How much testing is actually required?

The short answer: it depends on your building codes and risk tolerance. NFPA 110 sets out classes and types of emergency power systems, and that level of rigor matters for hospitals, data centers, or life-safety applications. For a typical office, we do a scheduled test—weekly or monthly, depending on site requirements—plus an annual load test and inspection.

I'm not sure every municipality enforces the same schedule, so don't hold me to that. But the principle is universal: run the generator under load on a regular schedule so problems surface before the real outage. A quick visual check isn't enough. Put a recurring reminder on the calendar and treat it like a bill you can't ignore. Even a simple checklist builds a maintenance record that helps when inspectors or insurance teams ask questions.