Let’s be honest here. Most Code change seminars start at the beginning of the National Electrical Code (NEC), and by the time the class is over, we’re lucky if we get as far as Article 700. It is important that electrical professionals have a good grasp of Article 700—Emergency Systems, because most of us aren’t exposed to this on a daily basis. One common violation I occasionally run across is when designers attempt to power exit lighting and emergency lighting (that does not have battery backup) by using an Article 702 generator design.
I see many attempts whereby the design engineer attempts to simply “put everything in the building on the generator.” They feel that, since there is some type of backup power to the exit and emergency luminaires, they have done their job. This is incorrect. Any design attempt to use a generator to supply exit lighting and emergency lighting (life safety), automatically triggers Article 700 in the 2017 NEC. The generator in this instance does not fall under Article 702, Optional Standby Systems. The generator now becomes a true emergency generator, covered under Article 700, and installation requirements become much more stringent.
The term “emergency generator” is used loosely in the electrical industry. If a generator system is used as part of an emergency system that supplies life-safety loads, it must be designed to meet the requirements of NEC Article 700 as well as NFPA 110. NFPA 110 is a standard referenced in the informational notes in the scope of Article 700.1.
In all the times I’ve had to remind an electrical engineer that a generator feeding non-battery backup exit sign luminaires and emergency luminaires is an Article 700 system and not an Article 702 system, I’ve never had one argue with me. They just kind of get real silent on the other end of the phone line—sometimes I've even had to ask if they are still there.
After a bit more research, they all were willing to revise the electrical designs. In some cases, the designer of record would even revert back to using exit lighting and emergency lighting with battery backup, since this relieved compliance with the more stringent emergency generator requirements.
For an Article 700 system, if the generator is located outside of the building, it needs to be in a weatherproof enclosure as Article 700.12(B)(6) states and NFPA 110 (2013) Section 7.2.2 mandates. The enclosure must be capable of resisting the entrance of snow and rain at the maximum wind velocity for that particular jurisdiction. The enclosure also must minimize the damage that can result from flooding. In certain low-lying areas, this can be an important concern, and the generator may need to be elevated.
Since NFPA 110 does not attempt to define every possible emergency scenario, all of the responsibility falls back to the NEC professionals. Page 964 of the 2017 NEC Handbook shows us an example of one such generator enclosure for an emergency system. The generator manufacturer can usually assist with any design issues.
In general, NFPA 110 defines an Article 700 generator supplying life-safety loads as a Level 1 system. The various classification levels (Level 1, Level 2) have to do with system installation, performance, and maintenance. For a Level 1 system, the enclosure must be heated and maintain a temperature of at least 40 degrees Fahrenheit. This is a serious concern for many locations that experience extremely cold weather. It can be a challenge, but speaking as someone who enforced these installations in Wyoming where temperatures frequently fall below zero, I can state for the record that it is very possible to accomplish. Conversely, an Article 700 generator system must also be designed to anticipate heat, and a cooling system must be selected for a Level 1 system, per NFPA 110 Section 18.104.22.168. This is to prevent overheating of the prime mover under conditions of the highest anticipated ambient temperature and when fully loaded.
With the implementation of the 2017 NEC, disconnect requirements for all permanent generator systems have changed. Article 445.18(B) requires all generators to be provided with a specific type of disconnecting means to shut down the prime mover. These new requirements can be found in NEC Article 445.18(B)(1) and NEC Article (B)(2):
- The shutdown means shall disable the prime mover start control circuits, and must render the prime mover incapable of starting.
- The shutdown mechanism must employ a mechanical reset.
It is important to note that, for any generator greater than 15 kilowatts (emergency or optional), there must be an additional disconnecting means. For an outdoor emergency generator, this disconnecting means must be located somewhere outside the generator enclosure. Jumping ahead to Article 700 for a second—at first glance, it may seem that Article 700.12(B)(6) creates some type of exception to 445.18(B) to allow for a single disconnecting means only. Don’t fall into this trap. Let’s take a minute to review the code language:
“Where an outdoor housed generator set is equipped with a readily accessible disconnecting means in accordance with 445.18, and the disconnecting means is located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure.”
What Article 700.12(B)(6) speaks of is the disconnecting means for the building and is merely stating that the 445.18(B) disconnecting means for the generator can be used to meet Article 225.31 and 225.32 requirements. The 2017 NEC Handbook confirms this. In my opinion, the sentence should have been written like this:
“Where an outdoor housed generator set is equipped with a readily accessible disconnecting means in accordance with 445.18, and the disconnecting means is located within sight of the building or structure supplied, an additional disconnecting means for the building shall not be required where ungrounded conductors serve or pass through the building or structure.”
Article 700.12(B)(6) points to an entirely different Code requirement and has no detrimental effect on 445.18(B). So don’t be confused here—generators with greater than a 15-kilowatt rating must still be provided with two 445.18(B) Code-compliant means to shut down the prime mover start controls. This holds true for both interior and exterior generators greater than 15 kilowatts.
And just to recap—if there is a generator enclosure, the second disconnecting means must be located somewhere outside of the generator enclosure.
There are many, many requirements for generators used in emergency systems, and the 2017 NEC and NFPA 110 cover them. I've mentioned only some of the requirements. Emergency generators housed indoors have their own unique set of rules (I haven’t even touched on these). The codes and standards that I’ve covered here are just the tip of the iceberg but are necessary for electrical contractors, electrical inspectors, plans examiners, architects and engineers to familiarize themselves with. I see violations of these requirements on electrical plans more frequently than I care to admit. More often than not, it is an engineer inexperienced with emergency systems who just decides to “put everything in the building on the generator.”
Powering exit luminaires and emergency luminaires with generator power will trigger a plethora of additional requirements that must be incorporated into the design if the luminaires do not employ some type of battery backup. We as Code professionals need to be able to catch these mistakes so we can bring life-safety issues to quick resolution, ensuring proper safeguards are put into place. Electrical contractors need to be familiar with this not only because they are electrical professionals, but also so as not to waste time bidding on a huge Code violation.
Please share this article with someone who installs emergency systems or has the responsibility to enforce these types of installations.
Finally, it’s easy to write Code in retrospect. I will submit my proposed language above as a Public Input for the 2023 NEC cycle. Please feel free to copy it and do the same if you agree.