Page 12 - North American Clean Energy November December 2015

solar energy

2017 NEC
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Phby Hannes Knopf

EVEN THOUGH 2014 NEC has yet to be adopted in all 50 states, solar professionals are
already looking to what the next edition holds in store, particularly when it comes to rapid

shutdown. While the rapid shutdown requirement outlined in 690.12 became the highest-
proile—and perhaps most debated—addition to the current version, proposed revisions in
2017 NEC will take that a step further to efectively require shutdown at the module level.
2014 NEC rapid shutdown is fairly inclusive of all PV architectures and technologies,

prescribing a 10-foot keep-out zone, outside of which the PV system voltages must be figure 1: 2014 NEC
reduced to less than 30V in 10 seconds. (igure 1) However, 2017 NEC language proposes Rapid Shutdown requires
reducing that to just a one-foot boundary with an additional 80V limit stipulation, a “10 foot rule” for
essentially requiring a module-level disconnect. (igure 2)
controlled conductors.
Many presume this change was developed with irst responder safety in mind. But is
module-level shutdown—which would drastically alter how PV systems are designed and
installed moving forward—really safer? To date, no data exists to demonstrate that safety
increases are needed. According to the National Institute for Occupational Safety and

Health database, between 1984 and 2013, there were seven irst-responder deaths due to
electrocution, and all were related to AC medium-voltage overhead or downed power lines,
not rooftop PV.
figure 2: Pictorial
he North American PV industry can look to European markets for further guidance representation of 2017

regarding irst responder safety and PV. A German study titled “Assessment of the Fire NEC 690.12 proposal.
Risk in Photovoltaic Systems and Elaboration of Safety Concepts for Minimization of
Risks”, completed in March by the Federal Ministry for Economic Afairs & Energy, T̈V

Rheinland, and Fraunhofer concluded that PV systems do not pose any particular threat
to ire department personnel, provided they comply with safety clearances just as with
any other voltage-carrying electrical equipment. Fraunhofer, Europe’s largest application-
oriented research organization, completed an additional report in May titled “Recent Facts his signiicant fact was achieved in a market that does not mandate rapid shutdown at all,

about Photovoltaics in Germany.” It found, with more than 1.4 million PV plants installed let alone at the module level.
in Germany, to date, no ireighter has been injured by PV power while putting out a ire.
It is unclear if the new limit will result in an increase in irst responder safety since it
was chosen primarily because 80V is
greater than most modules’ maximum

voltage, rather than corresponding to a
recognized safety limit. According to UL
1310, the safe voltage in dry conditions is
60V and 30V in wet conditions (also 2014

NEC Chapter 9, Table 11(B)). he 80V
limit is not suiciently small enough to
avoid restart arcs and even an attenuated
line voltage of a single panel can provide

enough concentrated power to cause a ire
ignition.
Additionally, UL 62109-1 and 2014 NEC
outline 240VA as the safe limit (energy

hazard), which is a lower power level
than many modules in the market today.
But, the 2017 NEC removes the 240VA
reference altogether and potentially

exposes irst responders to a higher
voltage than prescribed by UL or current

12 nacleanenergy.com
NOVEMBER/DECEMBER 2015