Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Tips: Article 694, Wind Electric Systems

Among the three alternative energy sources covered by the NEC (fuel cells, solar, and wind), wind electric systems seem to have captured the largest market share. Wind systems come in a far wider range of designs than the other two.

While the iconic wind system is the large wind generator farm just off the coast of (country X), small wind systems available in kit form are supplementing electrical power in applications ranging from homes to industrial sites. Those that supplement are interactive with other power sources, and they have different requirements from those that serve as the standalone power source.

It's also worth noting that, though somewhat complicated, the electrical aspects of installing a wind system pale in comparison to the other aspects. An installation will draw upon a wide range of craft skills. Also, competency in tower erection is essential to completing the work safely and to having a reliable system. If your crew does not have at least one person who is trained and experienced in tower erection, you should not be installing one of these systems.

Let's address some highlights of the Article 694 requirements:

  1. The NEC differentiates between supplemental and standalone systems? Which way your system will serve is critical to know before you begin any sort of planning. One reason is if it's supplemental then Article 705 also applies.
     
  2. If you're installing a small wind system, you must install a surge protective device (Articles 280, 285) between it and any loads served by the premises wiring [694.7(D)].
     


  3. Article 694 has some maximum voltage requirements in subsection 10. These apply to small residential systems, and generally the design criteria of a wind power kit specified for the application will already have addressed these.
     
  4. You must size your conductors based not on average or typical turbine output, but on the maximum output [694.12(A)(1)]. Think about why this is so. From an engineering standpoint, it makes sense to consider even larger conductors than the NEC minimum. The cost of upsizing the conductors is relatively small, and it will make the system permanently more efficient. You may run into issues with being able to terminate oversized conductors, but you could probably resolve those by oversizing only your long run between the tower and the first junction box or disconnect.
     
  5. Follow the requirements of Article 240 when sizing overcurrent protection devices (OCPDs) for turbine output circuits, inverter output circuits, and storage battery circuit conductors and equipment [694.15(A)]. For the power transformer(s), follow 450.3.
     
  6. Don't mix ac and dc OCPDs. They don't work the same way. For dc circuits, use listed dc OCPDs [694.15(C)].
     
  7. You must provide a means of disconnecting all current-carrying conductors of the wind system from all other conductors in the building [694.20].
     
  8. New with the 2014 NEC is a requirement for a readily accessible manual shutdown switch. You must also post a shutdown procedure at the shutdown means [694.23(B)].
     
  9. You can use any Chapter 3 wiring methods (if used as permitted by the relevant Articles), and/or other wiring systems and fittings specifically intended for use in wind systems [694.30].
     
  10. These systems have specific bonding and grounding requirements [694.40]. But beware inconsistencies in the NEC in the usage of these two terms. See the Article 100 definitions. Always keep in mind that you bond to reduce differences of potential; grounding will not accomplish that.