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
Let's address some
highlights of the Article 694 requirements:
- 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
- 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)].
- 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.
- 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.
- 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.
- Don't mix ac and dc OCPDs. They don't work the same way. For dc
circuits, use listed dc OCPDs [694.15(C)].
- You must provide a means of disconnecting all current-carrying
conductors of the wind system from all other conductors in the building
- 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
- 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].
- 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.