How to Select Standby Generator

How to Select Standby Generator

1.    What are your power requirements?  Your power needs can certainly tie back to your available budget, however, the primary determining factor for generator sizing can be answered with the following question: In the event of a power outage, should the generator run the entire building or just emergency loads? When sizing a generator for an entire building, factors like peak demands during summer months and the amperage of your electrical service are relevant details. When sizing for emergency loads only, the emergency circuits need to be determined. For an existing structure, this may require the electrician to split the emergency circuits from your main electrical panel into a separate emergency panel. For a home standby system, this decision is typically homeowner preference. For a critical application such as a healthcare facility, certain loads may be required to have emergency back-up in order to meet code compliance.   

2.    Which fuel type?  The most common fuel types for emergency standby systems are natural gas, propane, and diesel. While gasoline may seem convenient, it’s typically viewed as a poor fuel choice for standby systems due to its relatively short life of stability. Cost can be a factor when choosing between a diesel or natural gas generator (or propane) since the cost difference can vary depending on the size of the generator. The availability of the fuel source is another important factor. Diesel and propane provide an ‘on-site’ fuel source but may require a re-fill during an extended power outage, where natural gas is pulled from the local utility. Local code requirements may dictate which fuel types are available to your area; for example propane may not be an option within city limits in some regions. In addition, the type of facility can sometimes dictate if an on-site fuel source is required.

3.    Who will install the equipment?  The general answer is a licensed electrician and may also require a licensed plumber, but the choice is most often up to the buyer. The key is to choose a reputable company with a history of installing standby generator systems. Some buyers may have a company in mind when deciding to purchase a generator while others may benefit from a referral. If the choice is unclear, one of our representatives would be happy to provide recommendations.

4.    Where will the generator be located?  The generator set should be located where it’s readily accessible for maintenance and repair, and high enough to keep rising water from reaching the generator. For outdoor and rooftop installations, comply with code requirements for minimum distance from combustible walls and building openings. For indoor installations, adhere to requirements for fuel supply, ventilation, exhaust ducting, and proximity to combustible materials. Typically the generator should be located as close as possible to the transfer switch and fuel supply.

For more info, see Generator Placement.

5.    If outdoors, which enclosure type?  A follow-up question:  Is there a local noise ordinance? Some areas require the sound level of the standby system to be within a specific decibel rating at the nearest property line. If a specific sound requirement exists, the target sound level will determine the type of generator enclosure. Many residential or light commercial generators come standard with a sound attenuated enclosure while industrial grade generators may offer several enclosure types ranging from a standard weather enclosure to a custom package to meet strict requirements.

6.    What is the voltage requirement?   Common low voltages for the U.S. are: 120/240 volts single phase, 120/208 volts three phase, 120/240 volts three phase, and 277/480 volts three phase. If you are unsure, your electrician can provide this information.

7.    Which type of transfer switch?  Transfer switches for emergency standby generator are usually the automatically controlled type. Manual transfer switches can be supplied for certain systems if preferred, although this lack of automation usually doesn’t come with much of a cost savings. The size of the transfer switch (amperage rating) and installation location should be determined by your electrician and may depend on the earlier question of “entire building or just emergency loads?” If the system is sized to carry the whole building, the transfer switch may need to be service entrance rated which incorporates a utility disconnect within the transfer switch cabinet. For commercial/industrial applications, several other transfer switch features are available such as bypass isolation, closed transition, and programmed transition.

8.    Any specific accessory requirements?  Accessory options will vary depending on the generator type. Residential or light commercial systems typically offer an optional remote annunciator panel which provides generator status and can be located in a preferred area indoors. Cold weather kits and remote monitoring are also available for many residential/commercial systems. For industrial systems, the number of available options is much greater, including an expanded list of communication options, enclosure lighting, alternator strip heaters, load centers, etc.

9.    Warranty duration?  The standard warranty for generator systems typically ranges from one year to five years depending on the generator type. Where a residential generator may come standard with a warranty ranging from two to five years, an industrial generator may come standard with a one or two year warranty and offer optional upgrades. It’s a good idea to understand the warranty duration and coverage of your standby generator, and ask for upgrade costs if you prefer an increased coverage.

10.  Who will maintain the equipment?  Just like your vehicle, your generator needs to be properly maintained to help ensure the equipment will start and run as expected during your next power outage. Unlike your vehicle, generators tend to be neglected for extended periods between power outages. This can result in equipment failure during that critical time when you need it. Whether you are a do-it-yourselfer or if you prefer the added insurance of a maintenance program, keeping your equipment maintained properly is highly important to ensure reliable operation.