Figuring out the correct size when installing a generator for a commercial or industrial customer is not a one-size-fits-all type of project. You need expert help from experienced industrial/commercial electrical contractors to ensure the job is done right.
Why Do Industrial and Commercial Companies Need Backup Generators?
Power outages happen everywhere and everyone has experienced them. At home, this is an inconvenience. For commercial and industrial businesses, a power outage can cripple them. For manufacturing companies, a power outage shuts down production which costs them while the equipment and workers are not working. For restaurants and grocery stores, a long power outage can result in thousands of dollars in food spoilage, as well as losses in sales because customers cannot shop there. These generators prevent losses associated with outages, keep businesses operating, and allow important building services to continue.
Square Footage of Location
Using the square footage of your location is a great starting point to help calculate the backup generator size you need. There are equations within the industry used for this purpose.
- For Retail applications such as grocery stores, convenience stores, restaurants, and most other retail establishments, the formula for calculating power needs is 50 kilowatts + 10 watts per square foot.
- For most other commercial applications, the formula is 50 kilowatts + 5 watts per square foot.
Full Load Capacity of the Site
Calculating the full-load capacity of a site requires a little more legwork and research to come up with an accurate number. Here are the steps to follow to help calculate this number.
- Look at your service panel and take full-load current measurements during peak usage.
- Clamp on an ammeter for each leg of the electrical service, and add these measurements together. This will provide you with the total amps used.
- Divide the total amps by three for three-phase current, or by two for single-phase current.
- Multiply the total amps divided by phase current number by the supply voltage and multiply it again by 1000 for the Kilowatts (kW) required.
- Next, add the power in kilowatts used by each emergency safety standby system following articles 700, 701, 702 and 708 of the National Electric Code (NEC) to the kilowatts. This provides you with the full load kilowatts number.
The formulas to calculate this size are:
- Total Amps × Supply Voltage / 1000 = Full Load Kilowatts
- Full Load Kilowatts × 0.25 = Reserve Capacity
- To determine the proper generator size at 100% power is Full Load Kilowatts + Reserve Capacity = Generator Size
Other Factors to Consider When Sizing a Generator
The square footage of a location and the full load capacity of the site are good indicators to estimate the size of the generator you might need, but here are some other factors to keep in mind:
- Number of customers/employees onsite
- Operating hours of the business – Does it have regularly scheduled hours each day? Different hours on different days? Or online 24/7?
- Voltage sag – This is a temporary drop that occurs when there is a short circuit or overload of electric motors. Some industries need to meet specific tolerances so this is a factor in some installations.
- Environment – Humidity, temperature, and the altitude of the building may impact how to size the generator.
In conclusion, sizing a backup generator for a commercial or industrial business is a complex process that can be extremely expensive if you make a mistake. At Tri-State Electrical Contractors, we have the experience to make the process smooth and trouble-free. To learn more, give us a call at (423) 800-2134, fill out our simple online form, or email us at email@example.com today.