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You can have the right generator and equipment, yet still end up with a job site that won’t power up. The culprit is often a voltage drop problem nobody caught during planning.

Too much resistance over a long wire run quietly robs your equipment of the voltage it needs to operate safely and efficiently. It’s one of those details that feels merely technical until you’ve seen what happens when it’s ignored.

In this guide, you’ll learn how to calculate voltage drop using proven formulas. Discover which factors have the biggest impact on your results. Also, learn how to apply a voltage calculator approach that holds up in the field.

What Is Voltage Drop and Why Does It Matter for Power Equipment

Voltage drop is silent. It doesn’t trip a breaker or throw an error code. It quietly robs your equipment of the power it needs to run properly.

Understanding it is the first step before you reach for any voltage drop calculator or start running numbers on wire size.

What Voltage Drop Is

Electrical current flows from a power source through a conductor to a load. Along the way, resistance in the wire fights as it flows. The result is a lower voltage at the end of the run than the one that left the source.

Think of it like water moving through a long hose. The pressure at the nozzle is never as strong as it is at the spigot. The longer the hose, the weaker the flow. Wire works the same way.

That gap between supply voltage and delivered voltage, that’s your V drop.

Why It Matters on the Job Site

Low voltage is hard on equipment. Motors work harder to compensate. They draw more amperes, run hotter, and wear out faster. Generators underperform, and sensitive controls misfire or shut down entirely.

On industrial sites, that means downtime, damaged equipment, or jobs that stall because a power problem went unnoticed until something failed.

Temperature-sensitive equipment takes the hit hard. Climate control units and other temperature control equipment require a stable voltage to maintain setpoints accurately. A weak electrical circuit reduces efficiency and compromises the whole system.

The Industry Threshold You Need to Know

The National Electrical Code (NEC) sets the standard. It recommends a maximum 3% voltage drop on any single branch circuit. The allowable voltage drop across the entire system, including the feeder and branches, should remain at or below 5%.

These are the voltage drop limits that protect equipment, ensure safety, and keep installations code-compliant.

Exceed them, and you’re risking performance and liability.

Key Factors That Affect Voltage Drop

Voltage drop doesn’t happen randomly. Six specific variables determine how much voltage your equipment loses before it ever reaches the load.

 Wire Size (Gauge)

Wire size is one of the biggest factors in any electrical circuit. A small wire means higher resistance. Higher resistance means more V drop. Wire gauge is measured in AWG; the higher the number, the thinner the wire. Thin wire fights current every foot of the run. 

For heavy industrial loads, conductors are sized in kcmil (thousand circular mils), where a larger circular mils value means lower resistance and less drop. Always match conductor size to the job, not just the minimum NEC requirement.

Wire Run Length

Distance kills voltage. The longer the current flows through a conductor, the more resistance it fights. A common job-site mistake is measuring only one direction. The electrical circuit runs out and back, so a 200-foot run is actually 400 feet of conductor. That error alone can push a system past allowable voltage drop limits before a single piece of equipment powers on. Always calculate total cable length, not just the distance to the load.

Current Load (Amperage)

More amps means more drop. As load current increases, so does the voltage lost across the conductor. Running equipment near its rated ampacity leaves almost no margin. A motor pulling close to its rated amperes on a long run will see a meaningful voltage drop, enough to affect performance. Use a voltage drop calculator to verify your numbers before committing to a cable size.

<h3> Conductor Material (Copper vs. Aluminium)

Conductor material directly affects resistance. Copper has lower impedance and carries more current through a smaller cross-sectional area. Aluminium is lighter and cheaper, making it common in large feeder runs and temporary power setups. But aluminium has higher resistivity, so the same wire gauge formula that works for copper won’t work for aluminium. Each material has its own constant in the voltage drop formulas. Use the wrong one, and your calculation is wrong from the start.

Temperature

Heat raises resistance. As the conductor temperature rises, electrons encounter greater resistance as they move through the wire. Outdoor summer job sites are a real concern, as are runs near generators or engine exhaust. The National Electrical Code (NEC) provides temperature correction factors for a reason. Ignoring them on a hot-weather job can push percentage voltage drop beyond acceptable limits even on a correctly sized wire. Factor in ambient temperature before finalizing your cable size.

Single-Phase vs. Three-Phase Systems

System type changes everything about how you calculate voltage drop. In single-phase circuits, current travels out and back on two conductors; resistance adds up fast on long runs.

Three-phase circuits distribute the load across three conductors. That balance reduces the effective resistance the circuit sees. The result is less drop for the same supply voltage, amps, and cable length.

For large industrial equipment and longer runs, three-phase is almost always the more efficient choice. The load’s power factor also plays a role, especially in three-phase systems, where reactance must be accounted for.

Voltage Drop Formulas You Need to Know

The right formula depends on your system type. Know which one applies to your electrical circuit before you run the numbers.

Single-Phase Voltage Drop Formula

VD = (2 x K x I x L) / CM

Each variable does a specific job. Here’s what they mean:

• VD – Voltage drop, in volts
• K – Resistivity constant of the conductor material. Use 12.9 for copper, 21.2 for aluminium.
• I – Load current, in amperes (amps)
• L – One-way cable length, in feet
• CM – Conductor size, in circular mils (the cross-sectional area of the wire)

The “2” accounts for the full circuit; current flows out and returns. Single-phase circuits carry both legs in the same run.

Worked Example

You have a 240V single-phase generator on a job site. It powers equipment 175 feet away. The load draws 45 amps. You’re running #4 AWG copper wire (41,740 CM).

Plug in your numbers:

VD = (2 x 12.9 x 45 x 175) / 41,740

VD = 203,715 / 41,740 = 4.88 volts

Now check your percentage voltage drop:

% VD = (4.88 / 240) x 100 = 2.03%

That clears the NEC 3% threshold for branch circuits. Your wire size works for this run.

If the number came back above 3%, you’d upsize to the next AWG, then recalculate.

Three-Phase Voltage Drop Formula

VD = (1.732 x K x I x L) / CM

The structure mirrors the single-phase formula. One number changes: 1.732 replaces the “2.”

That number is the square root of 3 (√3). Three-phase circuits distribute load across three conductors. The geometry of that distribution reduces the effective resistance of the run. The result is a lower voltage drop compared to single-phase at the same distance and load.

Here’s what each variable means:

• VD – Voltage drop, in volts
• 1.732 – Square root of 3, the phase multiplier for three-phase circuits
• K – Resistivity constant. 12.9 for copper, 21.2 for aluminium
• I – Load current, in amperes
• L – One-way cable length, in feet
• CM – Conductor size, in circular mils

Worked Example

Same job site. Same 175-foot run. Same 45-amp load. This time you’re running a 480V three-phase circuit with #4 AWG copper wire (41,740 CM).

VD = (1.732 x 12.9 x 45 x 175) / 41,740

VD = 176,243 / 41,740 = 4.22 volts

Percentage voltage drop:

% VD = (4.22 / 480) x 100 = 0.88%

Well inside the NEC allowable voltage drop limit 3%. Three-phase circuits handle longer runs more efficiently. That matters when you’re sizing cable for large industrial equipment spread across a job site.

A note on power factor and impedance: These formulas use resistance only. For most job-site calculations, that’s sufficient. For precision work, long cable runs, high-reactance conductors, or large kcmil cables, factor in impedance and power factor for tighter results.

Not sure which system fits your job site? HOLT’s team can help you spec the right generator or power distribution equipment for your run distances and load requirements.

Get Your Job Site the Power You Need with Holt Industrial Rentals

Accurate power starts before the first cable hits the ground. Know your load, run distance, and size your conductors right, and the rest follows.

HOLT Industrial Rentals supplies temporary generators, power distribution equipment, and temperature-control units designed for demanding job sites. Our team helps you match the right equipment to your actual electrical requirements and the closest available unit.

Don’t leave power delivery to chance. Call HOLT at 844.660.RENT (7368) or schedule a site assessment to get your next project wired correctly from the start.

Picking the right portable generator size isn’t complicated. But get it wrong, and you’ll pay for it in tripped breakers, damaged equipment, or wasted fuel. The size you need depends on your power requirements. 

In this guide, you’ll learn how to calculate your total power needs, understand the difference between running and starting watts, and match your power demands to the right portable generator size.

Why Choosing the Right Portable Generator Size Matters

Generator size affects everything: safety, reliability, and how long your equipment lasts. Getting it wrong has real consequences. 

Here’s what happens at both ends of the spectrum.

When You Undersize a Generator

An undersized generator struggles from the start. It can’t meet your total power demands, so it runs at or above its limit constantly.

That stress shows up fast. Voltage drops and breakers trip. Equipment that draws power inconsistently, such as air conditioners, compressors, sump pumps, etc, can overheat or burn out motors entirely.

On a construction site, an undersized portable generator means tools cut out mid-job. On a job site running an HVAC system, it means the air conditioning never quite keeps up, and the generator runs hot trying.

Examples of commercial HVAC systems by HOLT Industrial Rentals

The harder you push an undersized unit, the shorter its lifespan. It’s not built to sustain that kind of load.

When You Oversize a Generator

Oversizing feels like the safe choice. It isn’t.

A generator set running well below its rated capacity runs inefficiently. For diesel generators, low load operation causes wet stacking (unburned fuel builds up in the exhaust system and creates long-term engine damage.)

Oversized units also burn more fuel than the job requires. On a long-term construction site or during an extended power outage, that adds up fast. Your utility bills and fuel costs climb while your generator underperforms.

The Safety Risks of Getting It Wrong

An overloaded generator is a safety risk. Push a portable generator past its rated output and you risk overheating, electrical faults, and in serious cases—fire.

An improperly sized backup generator connected to your electrical system without the right transfer switch creates back-feed risk. That’s dangerous for utility workers and your own equipment.

Real Applications Where Size Gets Missed

A portable power setup for a small job site office looks simple. Add a space heater, a few device chargers, a laptop, and a coffee maker, and you’re already pulling more running wattage than most people expect.

Scale that up to a construction site running a compressor, power tools, and temporary lighting simultaneously, and the margin for error shrinks fast.

A standby generator sizing carries its own risk. An undersized unit can’t power an electric water heater, air conditioning, and basic lighting at the same time. During a power outage, that’s a problem you don’t want to discover after the fact.

How to Calculate Generator Wattage Requirements

The math behind generator sizing is straightforward. You just need to know what you’re powering and how much power each item draws.

Follow these steps, and you’ll have your total wattage figure in minutes.

Step 1: List Every Item You Need to Power

Start with a full list. Write down every piece of equipment that will draw power from the generator at the same time.

Don’t guess. Check each item’s label or manual for its power requirements. If something is missing from the label, the manufacturer’s website will have it.

Step 2: Find the Running Watts for Each Item

Running watts are the power an item draws during regular operation. This is your baseline figure for each piece of equipment. 

Most appliances and tools list running watts directly on their label. If yours lists amps instead, use this formula:

Watts = Volts x Amps

In the US, standard equipment voltage is 120V or 240V. Multiply your total amps by the voltage, and you have your running power.

Step 3: Identify Starting Watts for Motor-Driven Equipment

Some equipment needs a surge of power to start up. Air conditioners, compressors, sump pumps, and HVAC systems all draw significantly more power at startup than during normal operation.

An example of a Portable Diesel, Oil-Flooded Compressor by HOLT Industrial Rentals

This startup draw is called starting watts. It only lasts a few seconds, but your generator has to handle it.

Starting watts are typically two to three times the running wattage for motor-driven equipment. Check the label or spec sheet for the exact figure.

If your air conditioner runs at 1,500 watts but requires 4,500 watts to start up, your generator needs to handle that 4,500-watt surge even if it only lasts a moment.

Step 4: Add It All Up

Now put the numbers together.

Add the running watts for every item on your list. That gives you your total running wattage.

Then take the single highest starting watt figure from your list, usually your largest motor-driven item, and add it to your total running wattage.

Total Power Requirement = Total Running Watts + Highest Single Starting Watts

That final figure is your minimum power requirement. Your portable generator needs to meet or exceed it.

Step 5: Convert to Kilowatts or KVA if Needed

Generator output is often listed in kilowatts or KVA rather than watts.

The conversion is simple:

Kilowatts = Watts ÷ 1,000

So a total power requirement of 8,500 watts equals 8.5 kilowatts.

KVA figures account for power factor, the efficiency at which your electrical system uses power. For most portable generator sizing, kilowatts is the more practical unit to work with.

Use a Generator Wattage Calculator

If you’d rather skip the manual math, a generator wattage calculator can do the work for you. Enter your equipment list, and the tool automatically estimates your total power needs.

It’s a helpful starting point, especially for complex job sites or facilities with extensive equipment lists. Use it to get a ballpark figure, then verify with the step-by-step method above.

So, How Big of a Generator Do You Need?

You’ve done the math. Now let’s apply it.

Generator size needs vary by application. A backup setup has different power demands than a commercial job site. Here’s how to match your total wattage figure to the right size generator for your situation.

Portable Generators for Small Remote Sites

A power outage at any site is inconvenient. A long one is a real problem, especially if you rely on medical equipment, or have busy security stations, or are located in an area with extreme temperatures.

For basic site backup, such as lights, a freezer, device chargers, and a few small lab appliances and terminals, a 3,000 to 5,000-watt portable generator covers most needs.

If you want to run central air conditioning, an electric water heater, and multiple appliances simultaneously, plan for a minimum of 7,500 to 10,000 watts.

Whole-site generators that power everything in a small site typically start at 10,000 watts and go up from there. For small facility coverage, a standby generator connected through a transfer switch is usually the better long-term power solution.

Portable Generators for Medium-to-Large Job Sites

Construction sites have different demands depending on what’s running. A small site with basic power tools needs far less than a large site running compressors, HVAC, and heavy equipment simultaneously.

For light job site use such as power tools, lighting, and small equipment, a 4,000 to 8,000-watt portable generator handles the load.

Mid-size construction sites running a compressor, multiple tools, and temporary lighting need 8,000 to 15,000 watts of reliable power generation.

Larger sites with multiple power demands running simultaneously should consider commercial generator options starting at 15,000 watts or more.

Portable Generators for Commercial Use

Commercial applications vary widely. A small retail backup setup is a different beast from a large facility running HVAC, refrigeration, and complete electrical systems during an outage.

For small commercial backup power, e.g, office equipment, lighting, and basic systems, plan for 10,000 to 20,000 watts.

Mid-size commercial facilities running air conditioning, refrigeration, and multiple electrical systems need 20,000 to 50,000 watts of emergency power.

Larger commercial operations should consult with a power generation specialist before sizing. The variables, total amps, electrical system layout, and simultaneous load demands, get complex fast.

Portable Generator Sizes vs. Industrial Generator Rentals: When to Scale Up

Portable generators are practical. They’re mobile, easy to set up, and handle a wide range of power needs. But they have limits.

Here’s how to know when you’ve hit them.

When Portable Generator Sizes Aren’t Enough

Portable generators have a ceiling. For most units, that ceiling sits around 17,000 watts, or 17 kilowatts.

If your total power requirement exceeds that, you’ve moved past portable generator territory. Industrial generator sets, standby generators, and diesel generators pick up where portable power leaves off.

For industrial construction sites, manufacturing facilities, data centers, and critical infrastructure, power demands routinely run into hundreds of kilowatts. That’s a different category of equipment entirely.

HOLT Industrial Rentals specializes in exactly that range. If the power you need exceeds what a portable generator can deliver, our team can size and deliver an industrial generator rental tailored to your specific load requirements.

When to Consider an Industrial Generator Rental

A few clear signs tell you it’s time to scale up:

• Your site runs motor-driven equipment with high starting watts simultaneously
• You need continuous emergency power for days, not hours
• Your electrical system requires a dedicated transfer switch and professional installation
• Your application falls under the national electrical code requirements for commercial or industrial power
• Your total wattage calculation exceeds 15,000 to 17,000 watts

<h3> Renting Makes the Transition Easy

Buying an industrial generator set is a large capital commitment. Renting gives you the right size generator for the job without that investment.

You get the power supply you need, sized correctly, delivered on-site, and returned when the job is done.

Can I run a whole small building on a portable generator?

Yes, but you’ll need 10,000 watts or more to cover essential systems simultaneously. For full whole-house coverage, a standby generator with a transfer switch is the better long-term solution.

What’s the difference between KW and KVA?

Kilowatts measure actual power output. KVA accounts for how efficiently your electrical system uses that power. For portable generator sizing, focus on kilowatts.

Is a portable generator or standby generator better for backup power?

Portable generators are flexible and cost less up front. Standby generators start automatically during a power outage and are better suited to critical applications. Your power needs and outage frequency determine the right choice.

How long can a portable generator run continuously?

Runtime depends on fuel tank size and the load you’re running. Most generators run 8 to 12 hours on a full tank at 50% load. Push the load higher, and the runtime drops. 

For extended power outages that last days, a propane or natural gas generator with a dedicated fuel supply is a more practical backup power solution than a standard portable unit.

Explore Our Range of Portable Generators at Holt Industrial Rentals

Generator sizing doesn’t have to be a guessing game. You have the formula, the reference ranges, and the knowledge to make a confident call.

The next step is getting the right unit in your hands.

HOLT Industrial Rentals carries a full range of generator rentals, including portable power solutions and heavy-duty industrial generator sets. Every rental is delivered, installed, and supported by a team that knows power generation inside and out.

Don’t wait for a power outage to find out your generator can’t keep up.

Call 844-660-RENT (7368) to speak with a project manager today. We’ll assess your power requirements and match you to the right generator size.

Or schedule a site assessment online and get your power solution in place today.

Your backup generator looks fine sitting there. But looks don’t tell you much. The real question is: will it hold up when the power goes out, and your facility depends on it?

Most standby generators spend their lives running light loads or sitting idle. That sounds harmless, yet it isn’t. Without regular load bank testing, diesel engines build up deposits, alternators drift, and voltage regulators go unchecked. By the time you find out there’s a problem, you’re already in one.

In this guide, you’ll learn what load bank testing is, how it works, and how often you should do it. Discover the exact procedure to follow to keep your emergency power systems running reliably.

So, What Is Load Bank Testing?

Load bank testing puts an artificial load on your generator. It simulates real-world electrical demand to verify that your generator can handle full load conditions when actual power failure hits.

A load bank is a self-contained piece of equipment. It connects your generator and draws a controlled electrical load, just like your facility would during a real outage. The difference is that you control the test, pick the timing, and the conditions.

Why Idle Runtime Isn’t Enough

Your generator starts up during monthly tests. It runs for 20 minutes at light loads. That’s not the same as being ready.

Diesel engines need to work. Running a diesel generator at low loads for short periods causes wet stacking. This is a buildup of unburned fuel and carbon deposits in the exhaust system. Over time, this buildup reduces power output, increases the risk of overheating, and can create a fire hazard.

Running a load bank test tells you things idle testing never can. It confirms your generator can sustain its rated capacity. It puts real stress on the cooling system, coolant levels, and fuel pressure. It checks voltage regulator performance and frequency stability under actual electrical load.

How Does a Load Bank Work?

A load bank applies a controlled electrical load to your generator. It does this by converting electrical energy into heat through resistive elements. That heat gets discharged safely, usually through a built-in cooling system with fans.

Types of Load Banks

Not every load bank works the same way. The type you use depends on your generator and the test you’re running.

• Resistive load banks are the most common. They apply a pure resistive load, such as electric heaters or lighting systems. They test your generator at unity power factor and are used for most standard generator load bank testing.
• Reactive load banks go further. They include inductive and capacitive elements that simulate real-world loads like motors, transformers, and air conditioning systems. Inductive load banks test your generator under lagging power factor conditions. Capacitive load banks test under leading power factor conditions.
• Resistive/reactive combination units apply both simultaneously. These give you the most complete picture of how your generator sets will perform under actual facility conditions.

How Often Should Generator Load Bank Testing Be Performed?

Testing frequency depends on how your generator is used and what industry you operate in. Some facilities test once a year. Others are required to test more often. Here’s how to think about it.

The Baseline Standard

For most standby generators, annual load bank testing is the minimum. Once a year, you put the generator under full load conditions and confirm it performs to its nameplate rating.

If your generator supports critical operations, once a year may not be enough.

NFPA 110 Requirements

The National Fire Protection Association sets the standard for emergency power systems in the United States. Under NFPA 110, emergency power generators must be tested at 30% or more of their rated capacity for a minimum of 30 minutes every month.

If a generator fails to reach 30% of its rated load during monthly testing, NFPA 110 requires a load bank test to be performed. That test must run for a minimum of two hours at full load.

Testing by Industry and Use Case

Different operations carry different risks. Testing schedules should reflect that.

• Healthcare facilities run the strictest schedules. Hospitals and care centers depend on emergency power generators to keep patients alive. NFPA 110 compliance is mandatory. Many healthcare facilities run load bank tests every six months as a standard practice to meet code and manage risk.
• Data centers run on uptime. A power outage that takes down a server costs real money fast. Most data centers run annual load bank testing at minimum, with some running tests every six months. Their backup power systems are too important to leave to chance.
• Industrial and manufacturing facilities depend on prime power and backup generators to keep production running. Testing schedules here vary, but annual testing is standard. Facilities with older generator sets or high-demand operations often test more frequently.
• Construction and temporary power applications follow a different rhythm. Generators on job sites move around and take heavy use. Regular load bank testing keeps them reliable across projects.

Insurance and Risk Management

Your insurance provider cares about this too. Many commercial property and business interruption policies require documented generator testing as a condition of coverage. Skipping load bank testing or failing to keep records can affect your claim if a power failure causes losses.

Documented test records show your insurer, regulator, and team that your backup power systems are maintained and ready. That’s peace of mind with paperwork to back it up.

Generator Load Bank Testing Procedure

Knowing what load bank testing is and when to do it only gets you so far. The procedure itself matters just as much. Follow these steps to run a safe and practical test.

Step 1: Pre-Test Checks

Before you connect anything, inspect the generator. A load bank test puts your system under stress. You want to catch existing problems before the test.

Check the following:

• Coolant levels — top up if low
• Fuel pressure and fuel supply — confirm adequate fuel for the full test duration
• Exhaust system — look for leaks, blockages, or damage
• Oil levels — check and correct before starting
• Transfer switches — confirm they are functioning correctly
• Electrical connections — inspect for loose or damaged wiring
• Nameplate rating — confirm the generator’s rated capacity before sizing your load bank

Document everything you find. Any existing faults should be resolved before the test begins.

Step 2: Confirm Load Bank Compatibility

Match your load bank to your generator. The load bank must be rated to handle the full electrical load of the generator set you’re testing.

Check voltage compatibility between the load bank and the generator’s power output. Confirm the load bank type suits your testing goals.

If the ratings don’t match, stop. Using the wrong load bank can damage your generator or produce inaccurate results.

Step 3: Connect the Load Bank

Connect the load bank to the generator’s power supply terminals. Follow the manufacturer’s connection instructions exactly.

Keep all connections tight and secure. Loose connections under full load create heat, arcing, and potential fire hazards. Double-check everything before you start the generator.

Step 4: Start the Generator and Stabilize

Start the generator and let it run unloaded for a few minutes. This gives the diesel engine time to warm up and reach normal operating temperature.

Watch the gauges. Confirm that the voltage output, frequency stability, and coolant temperature are all within the normal range before you add any load. If anything looks off, shut down and investigate.

Step 5: Apply Load Incrementally

Begin applying the load in steps. Start at 25% of rated capacity. Hold that level for a set period, typically 10 to 15 minutes, before moving to the next increment.

Progress through 50%, 75%, and then 100% of rated capacity. At each step, record your readings. Give the generator time to stabilize at each load level before increasing further.

Step 6: Monitor Performance

Active monitoring is the core of the test. Don’t just apply the load and walk away.

Track these metrics at each load increment:

• Voltage output — stable across all load levels?
• Frequency stability — holding at rated frequency?
• Operating temperature — staying within a safe range?
• Coolant temperature — is the cooling system keeping up?
• Fuel pressure — consistent throughout the test?
• Power factor — within acceptable range?
• Exhaust condition — watch for excessive smoke or unusual emissions

Step 7: Shut Down and Cool Down

Once the test is complete, reduce the load in reverse steps. Drop from 100% back to 75%, then 50%, then 25%, then zero. Never remove the whole load all at once; sudden unloading can damage the alternator and voltage regulator.

After the load is removed, let the generator run unloaded for a cool-down period.

Step 8: Post-Test Inspection

The test doesn’t end at shutdown. A post-test inspection confirms that the generator passed the test in good condition.

Check the following after shutdown:

• Exhaust system — look for new leaks or damage
• Coolant and oil levels — top up if needed
• Electrical connections — check for heat damage or loosening
• Overall condition — note anything that changed during the test

Document your findings alongside your performance data. A complete test record includes pre-test conditions, all performance readings, and post-test inspection results.

Having Issues with Your Generator? Call Holt Industrial Rentals for Help Today

Your backup power system is only as reliable as the last time you tested it.

Load bank testing is how you know your generator will hold up during a real power outage.

HOLT Industrial Rentals carries load bank rental equipment and industrial generator rentals to support your testing and backup power needs, delivered on-site and backed by an experienced team.

Don’t wait for a power failure to find out your system isn’t ready.

Call 844-660-RENT (7368) or schedule a site assessment today.

Power outages don’t send a warning. One minute, your operation is running. The next, it’s not.

Choosing the right generator type isn’t a small decision. The wrong call can undersize your power supply, stall your job site, or leave your facility dark when it matters most.

You have options such as diesel generators, natural gas, propane, solar, inverter generators, and more. Each one fits a different need, a different fuel source, a different job.

In this guide, you’ll learn the different types of generators, how each one works, and how to match the right power source to your application.

What Types of Generators Are There?

Generators convert mechanical energy into electrical energy. The type you pick depends on your fuel source, your power output needs, and how long you need it to run. Here’s a breakdown of each type.

Diesel Generators

Diesel generators are the workhorses of industrial power generation. You’ll find them on construction sites, in hospitals, at data centers, and anywhere that needs heavy-duty, continuous electric power.

They run on diesel fuel. Which is widely available and stores well. That makes them reliable for long running times. Some industrial diesel generators can run 24 to 48 hours on a single tank before refueling.

• Power Output: 20 kw to 2,500 kw and beyond

• Best for: Construction sites, manufacturing facilities, large-scale industrial operations, emergency backup power.

Diesel generators are also fuel-efficient at high loads. The harder you push them, the better they perform. That’s why they’re the default choice for industrial generators and critical facilities.

One thing to plan for: emissions. Diesel units produce exhaust, so they need proper ventilation and must meet local emissions standards.

HOLT Industrial Rentals carries a range of diesel generator rentals built for exactly this kind of demand, heavy loads, long runtimes, and tough job site conditions.

An example of commercial and industrial generator rentals by HOLT Industrial Rentals

Natural Gas Generators

Natural gas generators connect directly to a gas line. You get a steady power supply as long as the line stays active.

They produce fewer emissions than diesel generators, which makes them a cleaner option for facilities with strict environmental standards.

• Power output: 10 kW to 2,000 kW 
• Best for: Facilities with existing gas infrastructure, commercial buildings, hospitals, standby power systems

Natural gas generators work well as permanent or semi-permanent backup power solutions. The fuel cost is also lower than diesel in most regions, making them a cost-effective long-term option.

The trade-off is fuel access. If a natural gas line goes down during a widespread power outage, your generator goes down with it.

Propane Generators

Propane sits in a tank on your site. Unlike natural gas, it doesn’t rely on a gas line. That gives you more control over your fuel source, especially in remote locations.

Propane burns cleaner than diesel and has a long shelf life in storage, up to 30 years. That makes it a practical choice for backup generators that sit idle for months at a time.

• Power output: 5 kW to 150 kW
• Best for: Remote sites, rural facilities, light commercial backup power

Propane generators are popular for standby use. They start automatically when the power goes out and connect to your electrical panel through an automatic transfer switch. Runtime depends on tank size, but a 500-gallon tank can keep a mid-size unit running for several days.

Solar Generators

Solar generators use solar power to change a battery bank. The stored electrical energy powers your equipment through an inverter, converting direct current into alternating current.

They produce zero emissions and run silently. For remote monitoring stations, small job site offices, or temporary lighting setups, they’re a clean and practical option.

• Power output: 1 kW to 15 kW (most portable units)
• Best for: Remote locations, low-load applications, renewable energy setups, off-grid sites

Solar generators have limits. They depend on sunlight to recharge, so cloudy days or high-demand jobs can drain them fast. They’re best suited for light power needs, laptops, lighting, small equipment; not heavy industrial loads.

For large-scale or critical power generation, solar alone usually isn’t enough. Think of it as a supplement, not a primary power source.

Bi-Fuel Generators

Bi-fuel generators run on two fuel sources at once, typically diesel and natural gas. The diesel engine starts the unit and carries the base load. Natural gas feeds in to reduce diesel consumption as the load increases.

This gives you the reliability of diesel with the cost savings and lower emissions of natural gas.

• Power output: 100 kW to 2,000 kW
• Best for: Long-term industrial operations, facilities with access to both fuel types, applications where fuel cost and runtime matter

Bi-fuel systems are gaining ground in industrial settings where runtime is long and fuel efficiency matters. They can cut diesel consumption by up to 70% under the right conditions.

Inverter Generators

Inverter generators produce alternating current, convert it to direct current, then invert it back to clean alternating current. That process produces stable, consistent power with low harmonic distortion.

The clean power output matters for sensitive equipment such as laptops, medical devices, and electronics that don’t tolerate power fluctuations.

• Power output: 1 kW to 7 kW
• Best for: Small job sites, outdoor events, light commercial use, sensitive electronics

Inverter generators are quieter and more fuel-efficient than conventional portable generators. They adjust engine speed to match the load, which saves fuel and reduces noise.

They’re not built for heavy industrial loads. If your operation needs serious wattage, look at diesel or natural gas options.

Portable Generators

Portable generators are small, gas-powered units you can move from site to site. They plug in directly; no permanent connection to an electrical system required.

They’re common for construction sites with light power needs, small outdoor events, and as temporary backup power.

• Power output: 1 kW to 17 kW
• Best for: Light construction, job site tools, small events, residential backup power

Most portable generators run on gasoline. Runtime is typically 8 to 12 hours on a full tank. One important safety note: they produce carbon monoxide and must always run outdoors or in well-ventilated spaces. Never run one indoors or near open windows.

Standby Generators

Standby generators stay connected to your electrical system at all times. When the grid goes down, an automatic transfer switch triggers the unit and it starts within seconds.

They run on natural gas or propane and are designed for long automatic operation, no manual startup, no extension cords, no delay.

• Power output: 7 kW to 150 kW for commercial units; larger industrial standby systems go well beyond that
• Best for: Hospitals, data centers, commercial facilities, any operation where downtime is not an option

A properly installed standby generator keeps your operation running through blackouts without anyone lifting a finger. An electrician handles the installation and connects the unit to your electrical panel.

Industrial Generators

Industrial generators sit at the top of the scale. These are heavy-duty units built for continuous, high-load operation across large facilities, power plants, mining operations, and major construction projects.

They handle loads that smaller generators simply can’t. And they’re built to run for extended periods without a break.

• Power output: 50 kW to 3,500 kW and above
• Best for: Manufacturing plants, mining sites, refineries, large construction projects, critical infrastructure

Rental fleet includes industrial diesel generators sized for the most demanding applications, delivered, installed, and supported by an experienced team.

How to Choose the Right Generator Size

Picking a generator type is only half the decision. The other half is getting the size right.

Too small and your equipment strains or shuts down. Too large and you’re burning fuel and money on power you’re not using. Here’s how to find the right fit.

Start With Your Power Needs

Before you look at any generator spec sheet, figure out what you’re actually powering. Make a list of every piece of equipment that will draw power from the generator.

For each item, find the wattage. Most equipment has a label on the back or side that lists running watts and starting watts. Starting watts are higher, motors and air conditioning units pull a surge of power when they first kick on.

Add up all the running watts. Then add the highest single starting watt figure to that total. That number is your minimum power output requirement.

A licensed electrician can help you do this calculation accurately for large facilities. For complex industrial setups, it’s worth getting a professional assessment before you rent or buy anything.

Understand the Cost of Getting It Wrong

Undersizing is the more common mistake. A generator running at or above its rated capacity runs hot, wears out faster, and can trip or shut down at the worst possible moment.

Your electrical system suffers too. Voltage fluctuations from an undersized unit can damage sensitive equipment over time.

Oversizing has its own problems. Diesel generators, in particular, run poorly at low loads. Running a large diesel unit at under 30% capacity causes a condition called wet stacking. This is the incomplete combustion that damages the engine and shortens its lifespan.

The goal is to run your generator at 70% to 80% of its rated capacity. That’s the sweet spot for efficiency, performance, and long-term reliability.

Account for Running Time

Size and runtime are connected. A generator sized correctly for your load will run longer and more efficiently than one that’s constantly pushed to its limit.

Think about how long you need continuous power. A short-term job site need is different from a facility running backup power through an extended blackout.

For longer running times, factor in fuel storage and refueling logistics. A unit that’s right on your load limit will burn through fuel faster and need more frequent attention.

Consider Renting

Buying a generator means committing to one size. If your power needs grow or change, you’re stuck with what you bought.

Renting gives you flexibility. You can right-size the unit for each specific job or situation. If your load increases, you scale up. If the job wraps early, you send it back. There’s no capital commitment, depreciation, or maintenance costs sitting on your books.

For industrial operations, this matters. A planned maintenance shutdown has different power needs than an emergency outage response. Renting lets you match the generator to the moment, not the other way around.

HOLT Industrial Rentals carries a wide range of generator sizes for exactly this reason. Our team can assess your site and match you to the right unit before delivery. If your power needs shift mid-project, the rental can be adjusted.

For a deeper look at sizing options, see the Portable Generator Sizes guide for a full breakdown by application and load range.

FAQs

Do you need a transfer switch? 

Yes. A transfer switch connects your generator to your electrical panel and switches your power supply automatically when the grid goes down. An electrician will require one for any permanent setup.

Can you run a generator indoors? 

No. Gas-powered generators produce carbon monoxide. Always run them outdoors and away from windows and vents.

How long do industrial generators last? 

A well-maintained diesel generator can run 20,000 to 30,000 hours. Lifespan depends on load management, fuel quality, and regular servicing.

Can generators power air conditioning? 

Yes, but AC units draw a lot of power at startup. Always factor in that surge when calculating your load before sizing your unit.

Explore Our Range of All Generators Rental Types Today

You now know the different types of generators, how each one works, and how to size one for your power needs. The next step is finding the right unit for your specific job.

HOLT carries a full range of industrial generator rentals, including diesel, natural gas, and beyond. Every unit is delivered, installed, and supported by an experienced team that knows industrial power generation inside and out. If your load changes mid-project, the rental scales with you.

Your facility can’t afford downtime. You can get reliable electric power when and where your operation needs it.

Call 844-660-RENT (7368) to speak with a project manager today. We’ll assess your site, calculate your power needs, and match you to the right generator before a power outage forces your hand.

Or schedule a site assessment online and get a contingency plan in place.