NFPA 110: Standard for Emergency and Standby Power Systems is the most applicable standard in this regard. NFPA 110 addresses installation, testing and (most importantly) ongoing maintenance requirements for the EPSS. The issues that are examined in this article echo those identified within NFPA 110 and consist mostly of simple items that have outsized consequences if not properly addressed.

Here are five common reasons why generators fail, with additional information available in the previous issue:

1. Generator or related systems are in a vulnerable location
   1. Aside from engineers, few people appreciate the appearance of generators. Often, generators are consigned to out of sight locations that are less that optimal — on roofs, in basements, behind shrubbery. As multiple natural disasters have proved, these types of locations can make a generator just as vulnerable as the electrical utility services that they are intended to back up.
2. Weak or dead batteries
   1. Even with proper charging, batteries have a finite life expectancy. As such, NFPA 110 appendix section A5.6.4.5.1 recommends that batteries:
      1. Be tested semi-annually.
      2. If not tested, replaced every 24 to 30 months when exposed to temperatures exceeding 81°F for significant periods of time.
      3. Replaced every 36 to 60 months for cooler temperatures.
3. Bad fuel (diesel)
   1. It is recommended where fuel is stored for extended periods of time (more than 12 months) that the fuel be periodically pumped out and replaced with fresh fuel.
4. Generator controls not left in auto
   1. Auto Start turned off for maintenance or testing and technicians forget to return it to Automatic Start
   2. Indication/status needs to be visible in a common location for observation
5. Lack of testing with load
   1. This is a frustratingly simple problem. How do you know if a generator will work if you don’t test it? As stated before, most generators have very little run time. While NFPA 110 mandates monthly generator testing and an annual two-hour full load bank test, a surprising number do not comply with the load bank requirement.
   2. Also, many generator owners perform monthly tests consisting of running the generator under no-load for 30 minutes. Running a diesel generator excessively with little or no load can result in wet-stacking. Wet-stacking occurs when cylinder pressure and temperature does not reach a sufficiently high level, resulting in incomplete fuel combustion.

https://www.csemag.com/articles/five-more-reasons-generators-fail-when-you-need-them-the-most/