Portable Power? Let’s Learn How to Rent a Towable Generator

By Bob Ferrante July 10, 2020 View Profile

Generator rental is common on most any jobsite, although the reasons for seeking the power provided by this equipment vary. In some instances, the rapid expansion of residential and commercial areas means that construction will begin long before utilities are in place. The addition of units to existing buildings may require generators for construction trailers, or a contractor may need to power tower cranes on larger sites. In areas of high humidity and warmer temperatures, generators can be invaluable for operating dehumidifiers or air conditioners to assist in the drying of concrete or spray insulation in commercial buildings.

Regardless of the need, towable diesel generators are among the most prevalent solutions for jobsite power. This is due in part to the range of available sizes — from smaller 20-kW generators for building construction to 2-MW tractor trailers to support microgrids. These microgrids allow contractors to have their own utility infrastructure for working in more remote locations or on large sites. Towable diesel generators are also efficient, readily available and their portability is an attractive alternative to powering a generator with natural gas, which requires a gas supply or propane tanks on site. It should be noted, however, some states and municipalities prohibit the use of diesel generators due to emissions restrictions.

When choosing a towable diesel generator, there are key factors to consider to determine the right size and to ensure safe operation.

The Importance of Sizing It Right

Selecting the right size generator is critical — not only in terms of performance but also cost. A rental partner can help in selecting the proper size generator for the job, starting with a site survey or job walk of the construction project. The goal is to have a generator that provides enough power that it doesn’t become overloaded, which can lead to downtime and unnecessary costs for service or for returning the generator to a rental partner and having a new one delivered. Conversely, renting a larger generator than required to energize the site increases costs for rental fees.
Ultimately, it is not a one-size-fits-all situation, and it’s important to remember that the generator power that worked for a past project might not be the best option for a current one. That’s especially true considering the Tier 4 standards now in place to control emissions at a national level, as this affects the power load. Tier 4 standards are designed to reduce particulate matter and nitrogen oxides, two of the primary causes of smog and pollution.

Consider this scenario. Five years ago, a contractor may have rented a 56-kW generator for a construction site, but only used about 10 kW of the power at a time. The generator, in this case, was barely working. The rationale for renting a larger unit, however, was that the power would be there if it was eventually needed.

Today, Tier 4 compliant generators have to be operated at high enough load to clean the exhaust to lower emissions and improve air quality. Operating a generator at too light of a load will cause it to experience “wet stacking” (unburned fuel in the exhaust) and shut down, leaving the contractor without power. This leads to downtime, as well as increased costs for troubleshooting and potentially for service support. The key with generators is to operate them at a higher load to ensure they continue to run smoothly and provide the desired power. There are several questions a rental partner may ask to help determine the right size generator. These include:

What voltage and frequency are needed for the project?
What will the generators be powering (e.g., are there any large motors or tower cranes)?
What amount of power (current/amperage) is needed?
How far will the generator be from where it is tied in?
How will the power be tied in? Note that most rental companies will not do terminations. This job requires an electrical contractor.
How many hours per day will the generator be running?
In addition, the rental partner will also ask the contractor if fueling services are required for the generator as part of the rental program.

Maintaining Safe Operation

Safety is priority No. 1 on any construction site — and safe use of towable diesel generators is no exception. Generators should only be installed and operated by electrically trained personnel on a contractor’s team or by a rental partner, whose personnel are also fully trained. The generator must always be grounded, and safe fueling and refueling practices must be followed, including when using an external fuel tank. These tanks provide additional capacity, allowing contractors to extend the time between fueling — from twice a day with the tank on the generator, for example, up to four days with the external tank. This saves time and the cost for a fuel truck to come on site multiple times a day. Any fueling, regardless, must be managed by personnel qualified in proper procedures.

Each model of generator has specific starting procedures that contractors need to familiarize themselves with and follow accordingly. Upon setup of the generator, the rental provider can offer instruction on safe startup and operation of the generator.

Other Considerations

In addition to the right size towable diesel generator, there are also accessories to help effectively power the jobsite. They include distribution panels, circuit breaker panels and transformers. These distribution accessories offer much-needed versatility to power construction trailers, air conditioning, computers, lighting and more. They also provide additional outlets for tools. Renting these accessories along with their generators allows contractors to have a power generation solution that fits the size and scope of their project — and helps them get the job done on time and on budget.