CODEAPPLICATIONS BY MARK C. ODE
While many such facilities are already
operating successfully throughout the
United States, Article 691 will provide
technical details on the construction and
safety of these large facilities.
Three definitions have been provided.
“Electric supply stations” are defined as
locations containing the generating stations and substations, including their
associated generator, storage battery,
transformer and switchgear areas. A
“generating station” is defined as a plant
wherein electric energy is produced
by conversion from some other form
of energy, such as chemical, nuclear,
solar, wind, mechanical or hydraulic, by
means of a suitable apparatus. “
Generating capacity” is defined as the sum of
parallel-connected, inverter-rated maximum continuous-output power at 40°C
Section 691.4 requires large-scale PV
electric supply stations to be accessible
to authorized personnel only and to
comply with five requirements. The first
requirement is that the electrical circuits
and equipment shall be maintained and
operated by qualified personnel.
The second requirement is that
access to the PV electric supply station shall be restricted by fencing or
other adequate means in accordance
with 110. 31. The second paragraph of
110. 31 requires a wall, screen or a fence
to enclose an outdoor electrical instal-
lation to deter access by persons who
are not qualified within the facility. A
fence must be constructed at least 7 feet
high or a combination of 6 feet or more
of fence and at least 1 (or more) foot of
three (or more) strands of barbed wire
at the top of the fence. In addition, Table
110. 31 requires the distance from the
fence to any live parts to be a minimum
of 10 feet for 601 volts (V) to 13,799V, 15
feet for 13,800 to 230,000V, and 18 feet
for more than 230,000V.
The third requirement is that the connection between the PV electric supply
station and the system operated by an
electric utility for the transfer of electrical energy shall be made by connections
to medium- or high-voltage switchgear, substation, switchyard or similar
methods so as to safely and effectively
interconnect the two systems.
The fourth requirement of the electrical loads within the PV electric supply
station shall only be used to power auxiliary equipment for the generation of the
The fifth requirement is that large-scale PV electric supply stations shall
not be installed on buildings.
In addition to these requirements,
691.5 requires all electrical equipment
to be approved by listing and labeling,
field labeling, or—where products com-
plying with either of the above are not
available—by engineering review vali-
dating that the electrical equipment is
tested to relevant standards or industry
practice. Documentation of the con-
struction of the engineered electrical
design shall be provided upon request of
the authority having jurisdiction (AHJ)
based on 691.7. Additional stamped
independent engineering reports detail-
ing how the construction conforms to
the NEC shall also be provided to the
AHJ upon request.
The independent engineer designing
the system shall be a licensed professional
electrical engineer retained by the system
owner or installer. This documentation,
where requested, shall be available prior
to commercial operation of the station.
Section 691.8 requires the direct current
(DC) operating voltage calculation be
included in the documentation in 691.7.
For PV equipment disconnection,
691.9 permits isolating devices to be
more than 6 feet from the equipment
where written safety procedures and
conditions of maintenance and supervision ensure only qualified people service
the equipment. These procedures would
be in accordance with 110. 1 in the 2015
NFPA 70E standard. Buildings with the
sole purpose of housing and protecting supply-station equipment are not
required to comply with the rapid shutdown requirements in 690.12.
Since there isn’t a rapid-shutdown
system installed on the building, written
system shutdown procedures must be
available at the station site in the event of
an emergency. Where DC arc-fault circuit
protection is not provided, 691.10 requires
details of fire-mitigation plans to address
DC arc faults and must be provided in
the documentation required in 691.6.
Details of fence grounding and bonding
requirements must also be included in
the documentation in 691.6.
A New Look at PV Supply Stations
Article 691 in the 2017 NEC
THE 2017 NATIONAL ELECTRICAL CODE (NEC) will feature the new Article
691, which covers nonutility company, large-scale photovoltaic (PV) electric supply stations with generating capacities of at least 5,000 kilowatts (k W). Facilities
covered by this article will have specific design and safety features unique to large-scale PV facilities and will tie into the utility company grid, but will be operated
by private concerns.
OD E is a lead engineering instructor at Underwriters Laboratories Inc., based in Peoria, Ariz.
He can be reached at 919.949.2576 and
email@example.com. I S T