Don't Spec a Generator Backwards: A 5-Step Checklist for SDMO Buyers

Who Is This Checklist For?

This is for someone who's been given the task of buying a generator and isn't a power engineer. You're in operations, facilities, or admin procurement. You know the difference between a quote and an invoice, but maybe not between kVA and kW on a generator spec sheet. I've been there.

I'm an office administrator for a mid-size company—we handle about $500k in service orders annually across 8 vendors. I consolidated our facility needs after a 2023 office expansion. One of those needs? Backup power. I made some mistakes early on. This checklist is what I wish someone had handed me.

It covers 5 steps to make sure you don't spec a generator backwards—starting with the wrong number and ending with a machine that's either overkill or useless.

Step 1: Don't Count Lights. Count the Load.

Here's the classic rookie mistake: someone says 'we have 400 employees on three floors' and you think, well, that's a big generator. Maybe 200 kW. That's backwards.

You don't spec a generator based on the size of your building. You spec it based on what needs to stay on during a blackout. Is it the whole building, or just the server room, the HVAC for the main lab, and a few emergency circuits?

Your checklist here:

• Walk the facility with the facility manager (if you have one) or the IT lead.
• List every critical load: servers, security systems, refrigeration, specific production lines, lights for egress.
• Add up the running wattage (not the nameplate max, the actual draw).
• Then add 20-30% headroom for starting surges (motors, compressors).

I've seen a buyer order a 250 kVA generator for what they thought was a full building backup. When the electrician did the load calc, the actual critical load was 80 kW. They could have used a 100 kVA SDMO generator and saved $15,000. The vendor didn't correct them—they just took the bigger order. That's a transparency issue.

If your vendor isn't asking about your load list, that's a red flag.

Step 2: Understand the Kohler-SDMO Relationship (It's Not Weird, It's a Feature)

You're looking at SDMO generators. You see 'Kohler SDMO generator' in the search results. This looks like it might be a rebranding situation? It's not. It's a capability merger.

Kohler acquired SDMO in 2009. SDMO remains the manufacturing and engineering hub for the industrial diesel generator line in Europe and many export markets. So a Kohler-SDMO generator is basically a Kohler engine (or a Deutz/Perkins, depending on the size) integrated into an SDMO-designed enclosure and control system.

Why this matters to you:

• You get Kohler's global service network with SDMO's industrial generator engineering.
• Parts availability is generally excellent for the common models (20-1250 kVA range).
• It's a known quantity in the rental market, which means if yours goes down during a critical week, rental replacements are usually easy to find.

Don't get hung up on the branding. Focus on the support infrastructure in your region.

Step 3: Look for the 'Hidden' Specs (kW vs. kVA, Standby vs. Prime)

This is where inexperienced buyers get tripped up. Generators are rated in kVA but your loads are in kW. And those load numbers change depending on whether the generator is running full-time (Prime) or as a backup (Standby).

Here's the translation:

• kVA is the total capacity, including reactive power.
• kW is the real usable power. The ratio between them is the power factor (typically 0.8 for most industrial generators).
• Prime Power: The generator can run this amount for unlimited hours at a variable load.
• Standby Power: The generator can run this amount for a limited time during an outage (usually 200-500 hours per year) at a constant load.

A 40 kW SDMO generator (standby rating) might be listed as 40 kW or 50 kVA. A 50 kVA generator at 0.8 power factor gives you 40 kW. If you buy a 40 kW prime generator, you're buying a much more robust (and expensive) machine than a 40 kW standby unit.

For most office/administrative backup needs, the standby rating is sufficient and more cost-effective. But your electrician needs to confirm the load profile.

Step 4: Pay Attention to the Vibration Mounts (No, Seriously)

This sounds like a minor detail, but it's a major source of post-installation headaches. A diesel generator has a heavy engine and a rotating mass. If it's not properly isolated from the building structure, you'll get noise and vibration felt three floors up.

Anti-vibration mounts for diesel generators aren't an aftermarket add-on you should have to spec yourself. A good generator package—and SDMO's are generally good in this regard—comes with properly sized neoprene or spring mounts integrated into the skid base.

What to ask:

• 'Are elastomeric or spring vibration isolators included on the base skid?'
• 'For a rooftop or mezzanine installation, will an inertia base be required?'

I ordered a 200 kW unit years ago without verifying this. The generator itself was fine, but the building manager was getting complaints about a low-frequency hum from the floor below. We had to retrofit isolation mounts, which cost an extra $1,200 and required a crane to lift the unit. Not my finest moment.

Step 5: Don't Confuse a Portable Inverter with a Stationary Diesel

I see this question come up: 'how does an inverter generator work?' followed immediately by 'so should I get an inverter generator for my office building?' No.

An inverter generator works by converting the raw AC power from the alternator into DC, then inverting it back to a clean, stable AC signal. This allows the engine to speed up or slow down based on load, which saves fuel on small (<10 kW), portable units like a 4000 watt portable generator. They're quiet and efficient for camping or tailgating.

A diesel generator for commercial backup—like a 40 kW SDMO—operates at 1500 or 1800 RPM (depending on frequency and engine size). It doesn't vary speed. It produces bulk, reliable power. They're not the same tool. Don't go shopping for a generator for your office and end up looking at portable inverter units. You'll get the wrong product for the application.

If you need to understand the inverter mechanism for a small portable unit you're buying for a home or job site, that's a different conversation. For a fixed commercial installation, stick with the industrial diesel.

Common Mistakes I've Seen (and Made)

• Not checking noise regulations. A 40 kW generator at 7 meters is loud. You might need an enclosure or a residential-grade muffler. Ask for the dB rating before installation—not after. It's not a cheap retrofit.
• Assuming the fuel tank is included. Some generators come as 'base tank' (integrated into the skid). Others need a separate sub-base tank or a day tank. Clarify this. Running a fuel line from a distant bulk tank adds cost.
• Forgetting maintenance access. The generator needs air flow and space for a mechanic to lean into. Don't corner it into a closet. I've had a technician charge me for an hour just to squeeze past our storage boxes to get to the oil filter.

This checklist won't turn you into a generator engineer. But it'll keep you from making the expensive mistakes that happen when you treat a capital equipment purchase like a routine office supply order. And that, honestly, is the main goal for someone in my role.