Choosing the right commercial generator is one of the most important decisions a business can make before a power outage happens. Buy too small, and your generator may fail to carry the load when you need it most. Buy too large, and you may overpay for equipment, fuel, installation, and long-term maintenance.

For supermarkets, cold storage facilities, manufacturing plants, warehouses, data centers, medical facilities, food processing operations, and industrial sites, backup power is not a convenience. It is business protection.

A commercial power outage can shut down refrigeration, HVAC, production equipment, lighting, security systems, computers, pumps, compressors, and critical controls. In some cases, one outage can cost a business tens of thousands of dollars in spoiled inventory, lost production, emergency repairs, and downtime.

That is why the real question is not just:

“What size generator do I need?”

The better question is:

“What size commercial generator will safely power the equipment my business cannot afford to lose?”

Start With Your Critical Loads

The first step in sizing a commercial generator is identifying what must stay powered during an outage.

Some businesses need full-building backup. Others only need to support critical equipment.

Common commercial loads include:

• Refrigeration systems
• Freezers and walk-in coolers
• HVAC systems
• Lighting
• Security systems
• Point-of-sale systems
• Office computers and servers
• Pumps
• Compressors
• Production machinery
• Elevators
• Fire/life safety systems
• Battery chargers and control systems

For example, a supermarket may not need every outlet and light fixture powered during an outage, but it absolutely needs refrigeration, frozen food cases, coolers, critical lighting, cash registers, and security systems.

A manufacturing plant may need specific production lines, air compressors, controls, and safety systems.

A data center or telecom site may need clean, uninterrupted power for servers, cooling, UPS systems, and switchgear.

The generator should be sized around the equipment that matters most.

Do Not Size a Generator by Square Footage Alone

One of the most common mistakes commercial buyers make is trying to size a generator based only on building size.

Square footage does not tell the full story.

A 20,000-square-foot office building and a 20,000-square-foot food processing facility may have completely different power requirements. One may only need lighting, HVAC, computers, and security. The other may need refrigeration, motors, pumps, conveyors, compressors, and heavy production equipment.

A proper generator sizing process should consider:

• Total connected load
• Critical load
• Starting amps
• Running amps
• Voltage
• Phase
• Motor loads
• HVAC loads
• Refrigeration loads
• Future expansion
• Runtime requirements
• Emissions requirements
• Available installation space

This is where working with a knowledgeable generator supplier matters.

Know Your Voltage and Phase

Before purchasing a commercial backup generator, you need to know your facility’s electrical service.

The most common commercial and industrial generator voltages include:

• 208V 3-phase
• 240V 3-phase
• 480V 3-phase
• 600V 3-phase
• Medium-voltage configurations for larger industrial sites

Many commercial facilities use 480V 3-phase power, especially larger buildings, plants, and industrial operations. Smaller commercial properties may use 208V 3-phase.

This matters because a generator must match your electrical system or be properly stepped up or stepped down with transformers and compatible switchgear.

Buying the wrong voltage generator can create major delays, added costs, or installation problems.

Before shopping, confirm:

• Your building voltage
• Single-phase or three-phase service
• Main service amperage
• ATS size
• Existing switchgear
• Required generator breaker size
• Whether your equipment can accept multiple voltages

Understand kW, kVA, and Amps

Most commercial generators are sold by kilowatt rating, usually written as kW.

Examples:

• 100 kW generator
• 250 kW generator
• 500 kW generator
• 1000 kW generator
• 1500 kW generator
• 2000 kW generator

But commercial buyers also need to understand kVA, amps, and power factor.

In simple terms:

• kW is the usable power the generator can produce.
• kVA is the apparent power capacity.
• Amps measure current.
• Voltage affects how many amps the generator can provide.
• Power factor affects the relationship between kW and kVA.

For many industrial generators, a common power factor is 0.8.

That means:

kW = kVA × 0.8

So a 1250 kVA generator is commonly rated around 1000 kW.

This is why you may see a generator listed as:

1000kW / 1250kVA

Both numbers matter, but for most buyers, the kW rating is the easiest starting point.

Account for Starting Loads

Some equipment requires much more power to start than it does to keep running.

This is especially important for:

• Electric motors
• Compressors
• Pumps
• HVAC systems
• Refrigeration equipment
• Chillers
• Industrial machinery

A motor may run at one level but require several times more current during startup. If the generator is not sized properly, voltage can dip, equipment can fail to start, breakers can trip, or the generator can overload.

This is one of the main reasons commercial generator sizing should not be guessed.

A generator may appear large enough based on running load but still fail when multiple motors start at the same time.

Decide Between Whole-Building Backup and Critical-Load Backup

Commercial buyers usually fall into one of two categories.

1. Whole-building backup

This means the generator is sized to support the entire facility or nearly the entire facility.

This is common for:

• Medical facilities
• Data centers
• Large retail stores
• Critical infrastructure
• Some manufacturing plants
• Facilities that cannot tolerate operational interruption

2. Critical-load backup

This means the generator only supports the most important systems.

This is common for:

• Supermarkets
• Warehouses
• Office buildings
• Food storage facilities
• Small manufacturing sites
• Commercial buildings with budget or space limitations

Critical-load backup is often more cost-effective because the business protects what matters most without overspending on unnecessary capacity.

Choose the Right Generator Rating

Commercial generators are usually rated as:

• Standby
• Prime
• Continuous

These ratings are not the same.

Standby generators

A standby generator is designed for emergency backup power during utility outages. This is the most common choice for commercial buildings that only need backup power when the grid fails.

Prime power generators

A prime power generator is designed for longer run hours and variable loads. This is common for remote sites, oil and gas operations, construction, mining, temporary power, and locations without reliable utility power.

Continuous power generators

A continuous generator is designed for constant-load operation over extended periods. These are used in specialized industrial and power generation applications.

This distinction matters. A standby-rated generator should not automatically be treated as a prime-power machine.

Before buying, make sure the generator rating matches your real-world use.

Factor In Fuel Type and Runtime

Most commercial generators are powered by:

• Diesel
• Natural gas
• Propane
• Bi-fuel configurations

For large industrial and commercial applications, diesel generators remain very common because they are powerful, reliable, and widely available in used and surplus markets.

When choosing a generator, think beyond the kW rating.

You also need to know:

• How many hours of runtime you need
• Fuel tank size
• Fuel consumption at different loads
• Whether the unit has a base fuel tank
• Whether you need an external tank
• Local fuel storage rules
• Refill access during an extended outage

A generator with a large double-wall base fuel tank may be more attractive for businesses that need extended backup runtime.

For example, a supermarket, cold storage facility, or food distribution warehouse may need enough fuel to ride through a long outage without losing refrigerated inventory.

Check Emissions Requirements Before Buying

Emissions compliance is one of the biggest issues in commercial generator purchasing.

A generator that works in one state or application may not be legal or practical in another.

Before buying, confirm:

• Engine year
• EPA emissions Tier
• Emergency vs non-emergency use
• Standby vs prime application
• Local air district rules
• State-specific requirements
• CARB requirements, if applicable
• Runtime limitations
• Permit requirements

Common emissions categories include:

• Tier 2
• Tier 3
• Tier 4 Interim
• Tier 4 Final

For emergency standby use, older Tier units may still be suitable in some locations, depending on local rules and application. For prime power or non-emergency use, stricter emissions requirements may apply.

Do not assume a generator is acceptable just because it is available for sale.

Always verify the emissions requirements before purchasing.

Make Sure the Package Setup Fits Your Site

Generator sizing is not only about electrical output.

The full package matters.

Before purchasing, ask:

• Is the generator open or enclosed?
• Is it sound-attenuated?
• Does it include a fuel tank?
• Does it include a battery charger?
• Does it include a jacket water heater or block heater?
• Does it include automatic controls?
• Does it include a main breaker?
• What are the dimensions?
• What is the weight?
• Will it physically fit where it needs to go?
• Can service doors open properly?
• Is there enough airflow?
• Can a truck deliver it?
• Can a crane or forklift unload it?

Many buyers focus only on kW and price. That is a mistake.

A properly matched generator package should fit the electrical need, physical space, fuel plan, emissions requirement, and installation path.

Should You Buy New or Used?

A new generator can be a good option when lead time, budget, and exact specifications line up.

But many businesses get more value from a properly inspected used industrial generator.

Used commercial generators can offer:

• Lower purchase cost
• Faster availability
• Proven equipment history
• Immediate shipping options
• Strong value on high-quality brands
• Access to larger units at better pricing

The key is knowing what to look for.

Before buying a used generator, ask for:

• Generator nameplate photos
• Engine nameplate photos
• Alternator nameplate photos
• Hour meter reading
• Controller display photos
• Service records
• Load bank test report
• Oil sample, if available
• Current running video
• Photos of enclosure, breaker, radiator, tank, and controls
• Emissions documentation
• Included manuals and drawings, if available

A used generator can be an excellent purchase when it is properly vetted.

What Size Commercial Generator Do You Really Need?

There is no single answer that fits every business.

A small commercial building may only need 100kW to 250kW.

A supermarket, warehouse, or food processing facility may need 300kW to 1000kW or more.

A hospital, data center, manufacturing plant, or industrial site may need multiple megawatts of backup or prime power.

The correct size depends on the load.

At minimum, you should know:

• Your voltage
• Your phase
• Your critical equipment list
• Your running load
• Your starting load
• Your required runtime
• Your application: standby, prime, or continuous
• Your emissions requirements
• Your installation space
• Your preferred fuel type

Once those details are clear, the right generator becomes much easier to identify.

ARC Power Systems Can Help You Match the Right Generator

At ARC Power Systems, we help commercial and industrial buyers avoid the guessing game.

Our team can help review your project requirements and match you with a generator that fits your actual application, including:

• kW requirement
• Voltage and phase
• Fuel type
• Runtime needs
• Emissions requirements
• Enclosure type
• Tank configuration
• Controls
• ATS compatibility
• Physical dimensions
• Shipping and load-out planning

We focus on commercial and industrial power equipment, including used diesel generators, commercial standby generators, prime power generators, and large-scale power generation assets.

When available, we prioritize equipment with strong supporting documentation, trusted sourcing, service history, load bank testing, and current running proof.

Before spending serious money on a generator, make sure the unit fits your business.

Use our Power Match Tool to get started:

https://www.arcpowersystems.com/pages/use-our-powermatch-tool

Or contact ARC Power Systems directly with your voltage, phase, load requirements, runtime needs, and emissions concerns.

We will help you narrow down the right generator before you buy the wrong one.

Call ARC Power Systems today or use our Power Match Tool to get started.

📞 Call or Text: (213) 371-2848

📧 Email: sales@arcpowersystems.com

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Call ARC Power Systems today or use our Power Match Tool to get started.

📞 Call or Text: (213) 371-2848

📧 Email: sales@arcpowersystems.com