Test Your Medium-Voltage Knowledge of the NEC

Most electrical engineers in our industry spend the majority of their time working on systems that are rated 480V or less. Occasionally, they might find themselves facing a small amount of medium-voltage (MV) work that pops up on a primary service portion of a job. Most sections of the National Electrical Code (NEC) cover systems rated 600V and less; however, it also includes requirements for systems rated greater than that. A quick review of the NEC table of contents will reveal the sections that do have additional requirements for systems with higher voltage levels.

The most common MV system that a building engineer will encounter is a 15kV system, which is a standard electric utility distribution voltage. These systems are more precisely rated at 12,470V, 13,200V, or 13,800V, phase-to-phase. For systems rated a nominal 15kV, here are seven of the more common items you should be aware of as noted in various sections of the NEC when designing MV systems that meet the NEC.

Sweet is a senior associate and an electrical engineer/electrical commissioning agent with Mazzetti in Seattle. He can be reached at [email protected].


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