A Brief Overview of NEC Article 702 as it Pertains to Generators
The classification of optional standby generators applies to systems in public or private facilities where the safety of human life doesn’t depend on the performance of the system. They are usually installed where loss of power will cause economic loss or detrimental business interruption. These systems are not legally required, so their parameters are much less strict. Portable generators do not fall into this category unless they are permanently connected to the premises wiring. Your AHJ must still inspect and approve these optional systems to make sure they are safely and correctly installed (NEC Article 702).
These systems are not legally required to have any sort of testing or maintenance done. However, it is a good idea to perform regular maintenance and testing to keep all equipment in working condition.
The calculated anticipated load must be in accordance with NEC article 220, or another method pre-approved by your authority having jurisdiction.
Transfer equipment is required for all standby systems, no matter if the system is portable or fixed. Whether your transfer equipment is manual or automatic, it must have the capacity for the full load that may be transferred.
Legally required and optional standby systems may be held on the same transfer switch. Emergency standby systems are the only systems that are required to have their own transfer switches.
A sign that indicates the type and location of any on-site optional standby power source must be placed at the service-entrance for equipment.
Optional standby wiring is allowed to inhabit the same raceways, cables, boxes, and cabinets as other general wiring.
Signaling to indicate malfunction and to let you know when the system is carrying a load is required by the NEC for optional standby systems. Many manufacturers sell prepackaged systems that will alert you to many more issues than is legally required. This is one area where more is better. If your system can alert you to more areas of change in your genset’s health, you will be more apt to catch small problems and remedy them before they become large ones.
Something to Consider
Although the requirements are much less stringent for optional standby generator systems, it is always a good idea to go above and beyond what is legally required. Maintenance, grounding and bonding, and notification systems are just a few areas where doing more than is required will greatly benefit you in the long run.
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Graduated from Idaho State University with a degree in Heavy Duty Diesel and Onsite Power Generation. Damien is a master tinkerer and has been working on anything with a motor since he was about six years old. Besides being a generator fanatic, Damien is also an avid snowmobiler and aspiring world traveler.