There is no true “one-size-fits-all” solution when selecting voltage for a commercial building, but there are various design criteria that can be utilized to help determine which voltage will fit a project best. The NEC states that there are 3 different voltage classifications in North America:
Low Voltage: 600V and below
Medium Voltage: 600V-100kV
High Voltage: 100kV and above
For most commercial building types in North America, low voltage systems are used. Although there are many different voltage configurations, the two most common voltage systems used within commercial buildings are 208Y/120V and 480Y/277V. These voltages are classified as three phase systems and can be converted to single phase configurations. Medium and high voltage classifications are more useful in larger distribution fields such as industrial work and manufacturing buildings. Another reason to use medium or high voltage is voltage distribution and power transmission on a larger scale. Each voltage classification is important for design based on its application. When choosing the voltage for a commercial building, there are a few different factors to consider, including: Building type/size, what the building’s electrical loads are, and cost.
Building Type/Size:
A general rule of thumb when deciding between 208Y/120V and 480Y/277V for commercial buildings is that larger buildings will typically lean towards 480Y/277V. The smaller the overall footprint of the building, the more likely its power needs can be served by a 208Y/120V . Larger buildings tend to lean towards 480Y/277V configurations for a couple of good reasons. By putting certain loads on this voltage configuration such as HVAC equipment and lighting, it helps lower the overall cost by decreasing wire size based on smaller amperage required and mitigates the effects of voltage drop.
Building Loads:
The next consideration when determining the voltage supplied to a building is the type of electrical loads within the building. Every commercial building will include convenience receptacles and lighting fixtures, and most will include various owner supplied or HVAC equipment. Standard convenience receptacles are rated for 120V and are used to power most general equipment within a commercial building. Because of this, most commercial projects will require 208Y/120V power throughout the building. If 208Y/120V is the designed voltage configuration, then no additional steps are required to serve these pieces of equipment. For commercial projects with small HVAC loads and standard office-style equipment, providing only 208Y/120V should be sufficient.
However, if 480Y/277V is the chosen voltage configuration, step-down transformers will be required to provide 208Y/120V power within the building. A 480Y/277V system may be preferred for some projects as they can be more energy/financially efficient if larger pieces of equipment, with more electrical needs, are part of the design. Many times, this decision is driven by electrical demand of the HVAC systems being provided within a building. For example, equipment sized at 208V configuration will have more of an amperage draw than a 480V configuration. So if choosing 480V over 208V, not only does it lead to a smaller amperage output, it leads to smaller breakers and wire sizes. If you have a lot of equipment on a project this decision could save a lot of money.
Project Budget:
In any construction project, cost will always be a consideration when making design decisions. Choosing the voltage configuration to serve the building is no exception. Below are a few comparisons on how either a 208V or 480V configuration can be more cost-efficient in a commercial building:
Amperage:
208V systems would require more amperage than the same building on 480V systems. Choosing 208V on a project that has a lot of amperage requirements will lead to larger, more costly equipment. Choosing a 480V configuration for a project like this would be lower cost.
Conduit and Wire Size:
208V systems would require larger conduit and wire sizes on a bigger scale job. The more amperage that is required, the more the conduit and wire size will increase. Utilizing 480V instead would help keep the conduits and wire sizes smaller. Depending on the size of the building, this can save a lot of the projects budget.
Lighting:
Most commercial grade light fixtures are selectable in either 120V or 277V single phase. Utilizing a 277V service on the lighting will create less circuits throughout the building and thus cheaper since more lighting fixtures would be able to be on one circuit. This helps cut costs in breaker space required in the panel lights are being served from.
Additional Equipment:
480V configurations on most commercial applications would require step down transformers. As discussed, most buildings will require 120V connections for standard receptacles. Step-Down transformers are needed to step down electrical voltage to get to a 120/208V configuration to be able to provide a single-phase connection to the receptacles. The cost of these can get expensive depending on the size and quantity needed throughout the project. Utilizing a 208V configuration on a smaller project would help reduce costs in this scenario.
While there is no “one-size fits all” solution when selecting the voltage for a commercial building, if the building type/size, electrical loads, and project budget are considered, it can help narrow down the best answer for the design.
Sources
(2023). National electrical code handbook. National Fire Protection Association.
Written By
Steven Nickerson
Senior Electrical Designer
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