For questions about the National Electrical Code, NFPA 70. Just about all US jurisdictions that have adopted an electrical code use the NEC, often with a handful of local or state level amendments.
The National Electrical Code (NFPA 70 or the NEC) is the de facto standard for electrical installations in the USA. Most local and state jurisdictions have adopted the NEC, often with local amendments, or a code that substantially conforms with the NEC (such as the California Electrical Code).
The NEC is revised by NFPA on a triennial cycle. Most larger jurisdictions will stay current with the NEC, or at most 1 or 2 editions behind (so, given that the current NEC is the 2017 edition at the time of this writing, many jurisdictions are still on the 2011 or 2014 editions of the NEC).
Querents should state their locale, as usual -- there are cases where local amendments to the NEC are significant, and there also are some differences between editions (especially with regards to circuit protection requirements). Note that while the NEC as a whole applies to all occupancies where electrical power, light, control, or communications circuits are present irrespective of power source, there are many sections of the NEC that are only applicable to specific occupancies or use cases.
