How To Size A Generator For A Commercial Building?

Getting the right sizing of a generator for a commercial building requires careful consideration of various factors.

A properly sized generator ensures the building can continue to function during power outages, reducing the risk of business interruption and loss of revenue.

In this guide, we will explore the key factors to consider when sizing a generator for a commercial building.

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how to size a generator for a commercial building?

The following are the steps of how to size a generator for a commercial building.

Step 1: Calculating the Total Power Requirements (Load Estimation)

To size a generator for your commercial building, start by calculating the total power requirements.

List all critical equipment such as computers, servers, refrigeration units, security systems, and lighting. Check the power ratings (in watts or kilowatts) of each item.

If the rating is in amps, multiply it by the voltage (120V for single-phase or 208/240V for three-phase) to convert it to watts.

Motors and compressors in particular can have a higher starting surge than their running power. Account for this surge when calculating the total power requirements.

Identify Critical Equipment

List all the critical equipment, such as computers, servers, refrigeration units, security systems, and lighting, essential for your business operations.

Determine Power Ratings

Check the power ratings (in watts or kilowatts) of each item on your list.

If the rating is in amps, multiply it by the voltage (120V for single-phase or 208/240V for three-phase) to convert it to watts.

Consider Starting Surge

Some devices, such as motors or compressors, have a higher starting surge than their running power.

Account for this surge while calculating the total power requirements.

Step 2: Understanding Load Diversity and Power Factor

Load diversity is crucial as not all equipment is at maximum power at the same time. This knowledge is crucial for accurately sizing the generator.

Load Diversity Factor

Consider the probability of all equipment running at their peak power simultaneously. Peak loads are often experienced at specific times, such as the start of the workday or lunch.

To account for this, apply a load diversity factor of 0.6 to 0.8 to your total power requirements.

Power Factor

The power factor is the ratio of real power (kW) to apparent capacity (kVA) in an electrical system. It accounts for power losses due to reactive loads.

Commercial buildings typically have a power factor of around 0.8 to 0.9. Make sure to use the appropriate power factor while sizing the generator.

Step 3: Selecting the Right Generator Capacity

After considering the total power requirements, load diversity, and power factor, it’s time to choose the generator size.

Oversizing Consideration

To ensure no power disruptions, consider the cost of purchasing, maintaining, and operating an excessively large generator.

Aim for a balance between adequate capacity and cost-effectiveness.

Fuel Type and Availability

Select a generator that runs on a fuel type readily available in your area. Common options include diesel, natural gas, propane, or bi-fuel generators.

Generator Type

Decide between a standby generator (automatic operation during power outages) or a prime power generator (used for continuous, extended hours of operation).

The type of generator affects the sizing and cost.

Step 4: Consulting with a Professional

Consult a qualified professional or electrical engineer for generator size and installation requirements.

Based on your commercial building’s electrical system and specific needs, they will recommend the appropriate generator size.

Step 5: Regular Maintenance and Testing

Once the generator is installed, remember to perform regular maintenance and testing.

This ensures the generator remains in optimal condition and is ready to perform during an emergency. Create a maintenance schedule.

Conduct load testing periodically to verify that the generator can handle the intended load.

Refer to the table below for a general guideline.

Building Size	Generator Size
5,000-10,000 sq. ft.	25-45 kW
10,000-20,000 sq. ft.	45-100 kW
20,000-30,000 sq. ft.	100-150 kW
30,000-40,000 sq. ft.	150-200 kW
40,000+ sq. ft.	Consult a professional

Factors to Consider When Selecting an Extension Cord

Sizing a generator for a commercial building is important. Here are the steps to follow:

Length of the Extension Cord

Choose an extension cord based on the distance between the power source and the device.

To minimize voltage drop and potential hazards, choose a cord long enough to reach without excessive slack.

If the cord is too long, it may cause power loss, affecting the performance of your devices.

A too-short cord can cause unsafe stretching or tugging, stressing the cord and the connected device.

Wire Gauge (AWG)

The wire gauge of an extension cord determines its capacity to handle the electrical current. Thicker wires have lower gauge numbers and can handle higher loads.

Use a cord with a lower AWG rating for heavy-duty appliances and power tools to prevent overheating.

A cord with a higher AWG rating is suitable for smaller devices with lower power requirements.

Extension cords should have the right wire gauge to carry electrical current safely without overloading.

Power Rating (Wattage Capacity)

Verify the extension cord’s power rating, usually in watts or amps, to ensure it can handle the total power of your devices.

Exceeding the cord’s capacity can lead to overheating and pose a fire hazard. Add up the wattage of all the devices you’ll be using with the extension cord to determine its power rating.

Ensure that your cord can accommodate the combined power requirements of your devices.

Indoor vs. Outdoor Use

Different extension cords are designed for either indoor or outdoor use. They are weather-resistant and protect against moisture and UV rays, making them suitable for outdoor use.

Extending an indoor extension cord outdoors can cause electrical hazards due to the environment.

For safety and reliable performance, ensure extension cords are specifically designed for outdoor use.

Type of Plugs and Outlets

Verify that the extension cord’s plugs and outlets match the ones in your electrical system.

Maintaining a secure electrical connection requires compatibility to avoid any connection issues. Most extension cords come with standard three-pronged plugs and outlets.

Ensure that the cord’s plugs and outlets fit your devices and the available power sources to ensure proper operation.

Safety Features

Extension cords with grounded plugs (three-pronged) and outlets provide extra shock protection.

The third prong, known as the ground prong, diverts any potential electrical leakage safely into the ground.

Some extension cords come with built-in circuit breakers that automatically trip if the cord gets overloaded.

These safety features add an extra level of protection for both you and your connected devices.

Cord Jacket Material

The cord’s jacket material is crucial for its durability and resistance to abrasion. Common materials used for extension cord jackets are vinyl, rubber, or thermoplastic.

Choose a cord with a robust jacket suitable for the intended usage and environment. Choose an extension cord with a rubber or weather-resistant jacket if you plan to use it outdoors.

The jacket material plays a significant role in ensuring the longevity and safety of the extension cord.

Certifications and Standards

Opt for extension cords that meet safety standards and certifications, such as UL (Underwriters Laboratories) or ETL (Intertek).

These certifications ensure that the cord has undergone rigorous testing for safety and performance.

Those with these certifications are more likely to meet industry safety standards, reducing electrical hazards.

Cord Reel or Cord Management

Consider whether you need a cord reel for easy storage and organization.

Cord reels are a convenient way to prevent tangling and protect the cord from damage during storage.

After use, they retract neatly, reducing clutter and making it easier to find and use the extension cord.

Cord management solutions are especially beneficial if you frequently use extension cords for various tasks.

Overcurrent Protection

For added safety, consider using extension cords with overcurrent protection. Surge protectors are built into some extension cords to protect connected devices from power surges.

Overcurrent protection helps prevent damage to sensitive electronic equipment. It provides an extra layer of safety during sudden electrical surges.

For electronics like computers and televisions, surge-protected extension cords are a good choice.

Proper Usage and Maintenance

Follow the manufacturer’s guidelines for using the extension cord safely. Avoid running cords under carpets or rugs, as this can lead to overheating and pose a fire risk.

Check your extension cord regularly for signs of wear or damage, and never use damaged cords.

If you notice any fraying, exposed wires, or cracks in the cord’s jacket, replace it immediately.

To reduce the risk of electrical accidents, extension cords must be used and maintained correctly.

Recommended Extension Cord Sizes for Common Generator Sizes

When choosing an extension cord for your generator, select the right size to ensure the safe and efficient operation of your equipment.

Here are the recommended extension cord sizes for common generator sizes:

For generators up to 2,000 watts

Use a 16-gauge extension cord that is no longer than 25 feet in length.

A 16-gauge extension cord has a wire diameter of 0.0508 inches and can handle up to 13 amps of current.

For generators between 2,000 and 3,500 watts

Use a 14-gauge extension cord that is no longer than 50 feet in length.

A 14-gauge extension cord has a wire diameter of 0.0641 inches and can handle up to 15 amps of current.

For generators between 3,500 and 5,000 watts

Use a 12-gauge extension cord that is no longer than 100 feet in length.

A 12-gauge extension cord has a wire diameter of 0.0808 inches and can handle up to 20 amps of current.

For generators between 5,000 and 7,500 watts

Use a 10-gauge extension cord that is no longer than 100 feet in length.

A 10-gauge extension cord has a wire diameter of 0.1019 inches and can handle up to 30 amps of current.

For generators between 7,500 and 10,000 watts

Use an 8-gauge extension cord that is no longer than 100 feet in length.

An 8-gauge extension cord has a wire diameter of 0.1285 inches and can handle up to 40 amps of current.

For generators between 10,000 and 13,000 watts

Use a 6-gauge extension cord that is no longer than 100 feet in length.

A 6-gauge extension cord has a wire diameter of 0.162 inches and can handle up to 55 amps of current.

For generators over 13,000 watts

Consult with a licensed electrician to determine the appropriate extension cord size and length for your specific needs.

Ensure that the extension cord can handle the current load and voltage requirements of your generator to prevent overheating and potential safety hazards.

Potential Hazards of Using the Wrong Extension Cord Size

Using the wrong extension cord size with your generator can pose a number of potential hazards. Here are some of the risks you should know:

Overheating

If you use an extension cord that is too small for your generator can overheat and melt and can cause a fire.

This is because the smaller wires in the cord can’t handle the current load and become overloaded.

Voltage Drop

When using an extension cord that is too long or too small for your generator, a voltage drop can occur.

This means that the voltage output from your generator will decrease as the power travels through the extension cord, leading to inefficient operation and potential damage to your equipment.

Tripping Hazards

If your extension cord is too long or not properly secured, it can become a tripping hazard.

This is especially dangerous if you’re using your generator in an area with lots of foot traffic or where people may be working.

Electrical Shock

If your extension cord is damaged or not rated for outdoor use, it can pose a risk of electrical shock.

This is because the cord’s insulation is compromised, allowing electrical current to leak out and potentially harm anyone who comes into contact with it.

Equipment Damage

If you use an extension cord that can’t handle the current load of your generator, it can damage your equipment.

This is because the voltage output may fluctuate and cause the motor or other parts to malfunction, leading to costly repairs or replacements.

Tips for Using Extension Cords Safely and Effectively

Using extension cords safely and effectively is important to ensure the safe and efficient operation of your equipment. Here are some tips to keep in mind:

Choose the Right Cord

Always use an extension cord that is rated for outdoor use and can handle the current load of your equipment.

Check your equipment’s manual for recommended cord specifications, and choose a cord that is the appropriate length for your needs.

Inspect Your Cord

Before using your extension cord, inspect it for any signs of damage, such as cuts, frayed wires, or exposed insulation.

If you notice any damage, replace the cord before using it.

Use Ground Fault Circuit Interrupters (GFCIs)

If you’re using your extension cord with power tools or other outdoor equipment, consider using a GFCI adapter to help prevent electrical shock in case of a ground fault.

Avoid Overloading

Never overload your extension cord by plugging in too many devices or equipment that exceed the cord’s current rating.

This can cause the cord to overheat and potentially cause a fire.

Don’t Run Cords Under Rugs or Furniture

Running your extension cord under rugs or furniture can cause it to overheat and potentially cause a fire.

Always keep your cords on top of carpets and furniture, and avoid running them across high-traffic areas where they can become a tripping hazard.

Keep Cords Dry

Water and electricity don’t mix, so always keep your extension cords dry.

If you need to use your cords in wet conditions, consider using a cord with a built-in ground fault circuit interrupter (GFCI) to help prevent electrical shock.

Store Cords Safely

When not in use, store your extension cords in a dry, cool place away from direct sunlight and heat sources.

This can help prevent damage to the cord’s insulation and prolong its lifespan.

FAQs on Sizing A Generator For A Commercial Building

Final Words

Sizing a generator for a commercial building requires careful consideration of factors such as power load, equipment and appliance requirements, fuel type, and installation costs.

If you work with an electrician or generator installer, they can perform a load analysis and determine your building’s specific power requirements.

It is important to select the right generator and to follow proper installation and maintenance procedures to ensure reliable backup power.