America’s aging energy grid is increasingly subject to outages due to planned maintenance, overloads and severe weather events. What’s more, the substation system is undergoing one of the largest overhauls of the last 100 years as utilities modernize the grid to integrate renewables and other technologies, and this means more-frequent outages due to upgrade projects.

For support during planned outages, utilities often turn to temporary equipment providers for temporary substation solutions. These allow utilities to reserve their existing fleet for emergent events.

“The components are like Lego blocks that can be pieced together to conform to the configurations, voltages and protections utilities need,” said Eric Bateman, regional product development manager at United Rentals. You may need just a voltage regulator, just a transformer, or a complete packaged substation. The right provider will understand your needs and how to configure a safe, effective solution.

Solutions can be fixed or mobile. Mobile substations are a self-contained trailer or skid-mounted units or containers complete with all the elements of a permanent substation, such as power transformers, switchgear, protection and control panels, disconnect switches, and diesel generators if needed.

When deciding what temporary substation provider to choose, consider these factors.

Available sizes

United Rentals’ equipment ranges from 5 MVA to 25 MVA, with multiple power ratings ranging up to 138,000 kVA and many different Delta-Wye and Wye-Delta configurations. Access to a broad range of components enables the company to customize the most effective solution for the situation. “With our strategic partners and engineering capability, we can support multiple different voltages or configurations,” said Bateman.

Flexibility and scalability of the offerings

Flexibility and scalability on the part of a provider may be important depending on your needs — for instance, if you need multiple voltage configurations. “Let’s say the utility has five or six different substation voltages in their system,” said Bateman. “Rather than spending $3 million on each one of those mobile subs to fleet a backup for everything, United Rentals has the capability to put a voltage regulator on the lower side to allow a multiple tap.”

The available footprint

Compact footprints require a space-efficient substation. United Rentals can offload the equipment, put it on a pad mount or keep it on trailers, for example, to fit the available space.

Will it need a permit?

Heavy haul equipment must be rated for DOT and over-the-road standards and meet weight and dimension restrictions. Some mobile substations will need a special permit. Alternatively, the provider may choose to transport a mobile transformer separately from other equipment.

How is it tested?

The components should be tested prior to delivery as well as during commissioning.The provider should load-test the system with a false load on-site. “Some companies just have the equipment and drop it off,” Bateman noted.

Does the company understand isolation and grounding?

Safety is a primary consideration. “We make sure our electrical distribution equipment is properly grounded so that in the event of an electrical fault, people are safe,” said Bateman. In addition, the temporary system needs to be isolated from the permanent substation. “An independent ground gridding plan that isolates the temporary sub is a safety benefit for the workers, and we take that into consideration. Not every company does,” Bateman added. The provider should also understand arc flash calculations, the potential imbalances and impedances in the line, and high side and low side protection both on the fused or breaker side and on the regulated and nonregulated side.

As utilities struggle to meet the demands of an ever-evolving grid and network, the right temporary equipment provider can be a game-changer, especially when it comes to longer-term outage work.

Contact United Rentals for help with your power distribution needs.

Marianne Wait is an editor and writer who creates content for Fortune 500 brands.