Temporary Electrical Service Sizing for Construction Projects

Sizing and securing temporary electrical service is essential to any new construction project as it will serve as the only source of electricity until permanent power can be brought in.

Temporary size calculations must be as accurate as possible. Service that is too large can be very costly. If it’s too small, the project will be plagued with tripping breakers, insufficient electricity to power lighting, tools, and equipment, and hindered progress.

Here are a number of important items that must be taken into consideration when sizing temporary power for a construction project:

• How many construction trailers will there be, and what size? Calculations must allow for the trailers' HVAC needs, copiers, computers, coffee makers, space heaters, etc.

• What are the power needs for heating and cooling the building under construction? Keep in mind that HVAC may be required during summer months for drying finishes.

• Electrical power for lighting, tools, and battery chargers should be calculated by the square foot.

• Will there be special equipment present such as tower cranes, material elevators, sump pumps, dewatering systems, etc.?

• Will structural steel be erected using electrical arc welders, gas welders, or a combination?

• If the building will have passenger elevators, will temporary power be required during their setup and installation?

Construction is a dynamic process, so once the service size has been calculated, a good rule of thumb is to increase it by 15-20%. This allows spare capacity for the unexpected surprises and changes that occur on almost every construction project. It’s also important to ensure that the temporary service is properly located and won’t require relocation before the end of the project. It should be close enough to the building and construction trailers to avoid unnecessary voltage drop.

Different utility companies have different requirements for temporary power installations, but almost all require that a load calculation sheet showing how the electrical needs were determined be submitted and approved by the utility.