Portable vs. Fixed-In-Place Generators

Generators are manufactured to either be portable or fixed-in-place. Each has its own advantages and disadvantages.

Portable generators are useful because they can be moved from location to location. They are typically used though in smaller applications and are not permitted per NEC to be used for Emergency or Legally Required systems, which limits there use in commercial and industrial applications. They are most commonly used in residential applications and on construction sites where power is not available. These Optional Standby uses can be very important though during a natural disaster. During the 2004 hurricanes in Florida, the sound of generator engines was very common in residential neighborhoods as people awaited their power to be turned back on. A common 5550W generator is enough to supply power to a refrigerator, coffee maker, television and/or window air-conditioner.

Fixed-In-Place generators are commonly seen in commercial and industrial applications. They are becoming more popular in residential use but are not widely common. These types of generators can be very large which is why they are so common for large areas of assembly. Not to mention, they are required to be used per the NEC in Emergency and Life Safety situations. And the engine fuel that can be used is very diverse which is especially useful in retrofit projects. For more information about the code classifications regarding fixed-in-place generators, please read below.

Code Classifications of Generators

Chapter 7 of the National Electrical Code defines the three classifications of generator systems. They are:

• Emergency (Life Safety)
• Legally Required
• Optional Standby

This classification involves systems that supply loads that are essential to safety and life such as emergency lighting, exit signs, essential ventilation systems (especially in hospitals) and fire protection systems. Life Safety systems are installed in places of assembly such as high-rise buildings, schools, theaters, hotels, stadiums and any type of location where large groups of people gather. NFPA 101 dictates exactly the requirements for Life Safety applications. These systems are designed to provide illumination, during normal power outage, to ensure a safe means of exit. Life Safety systems also provide power for proper fire detection, continuous operation of fire pumps and fire alarm devices. Per NEC 700.12(B) it is required to maintain enough fuel on-site to provide no less than 2 hours of operation and the system must turn on within 10 seconds of normal power shutting off.

This classification is very similar to Emergency systems with regard to where they are required. The main difference between the two is that legally required standby systems are intended to provide electric power to aid in firefighting, rescue operations, control of health, elevator usage, hazards and similar operations. The main focus of legally required systems is to "get people out of the building". During a power outage, a legally required genset automatically (with 60 seconds) supplies power to selected loads that, according to NFPA 110, are not classified as emergency systems.

Optional Standby gensets are those that are not required by life safety, governmental agencies or the local AHJ. The requirements for these systems is dictated by the residential, commercial or industrial building owner(s), property managers and/or the businessses occupying them. Optional standby systems are intended to supply on-site power to selected loads either automatically or manually. The purpose for optional standby gensets is to maintain power, during normal power outages, to either preserve inventory, prevent heat/humidity damage or to maintain normal working conditions following a natural disaster (hurricane, earthquake, etc). These gensets can serve power to any system not classified as emergency or legally required such as power receptacles, hvac, domestic water booster pumps and water heaters, industrial machinery, freezers, refrigerators and/or UPS (uniterruptable power source) systems.

One important thing that needs to be mentioned in conclusion is that all three classifications refer to the entire system, not just the engine-generator. The National Electrical Code has specific guidelines regarding the type and location of transfer switches which are an integral part of the generator system. When assessing the specific transfer equipment requirements, review NEC 700.6, 701.7 and 702.6.

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