PV System Rapid Shutdown


Inside this Article

Like all microinverters, this Enphase S230 offers RSD capability by default.
SolarEdge offers a fully RSD-compliant solution with its Power Optimizers (DC-to-DC converters), which are designed to be installed with SolarEdge inverters.
This ABB low-profile RSD pass-through box fits behind a module, connecting to the series string positive and negative wires via the locking connector (H4) input leads. The output is connected to the output circuit routed to an ABB UNO or PVI inverter. This RSD solution is offered in one- or two-string models.
The Fronius Rapid Shutdown Box works with single or multistring arrays and with various Fronius inverters.
The Ginlong Solis RSD is offered in one- and two-string models, and connects directly to the PV strings via MC4 cables.
SMA’s TL inverter line offers limited backup power during the daytime with its SPS feature. The RSD solution shown here uses a remote switch, instead of loss of utility power, to initiate shutdown.
The Yaskawa-Solectria Solar Rapid Shutdown combiner can accommodate up to four input series strings and is compatible with its PVI transformerless inverter line.
The OutBack Power ICS Plus Combiner and RSI Initiator can work in grid-tied and/or battery-based systems, and are not dependent on using OutBack inverters.
The Bentek Rapid Shutdown system offers two- and three-string options for grid-tied inverters. The rapid shutdown controller shown here is used to initiate shutdown and is installed in an accessible location.
The Innovative Solar RSD is available as a SolaDeck flashed rooftop combiner or in a nonflashed, nonmetallic version. (An eight-string input version is also available.)
The MidNite Solar Rapid Shutdown system, which can be used in battery-based and grid-tied systems, includes the Birdhouse (above) that controls disconnecting combiner boxes (right) and remote trip breakers (not shown).
The Phoenix Contact SolarCheck RSD offers module-level rapid shutdown.
The Solar BOS line provides rapid shutdown of up to eight series strings, and works with grid-tied string inverters.

In 2014, section 690.12 “Rapid Shutdown of PV Systems on Buildings,” was included in the National Electrical Code to safely allow firefighters and emergency responders to easily and quickly shut down energized PV system circuits on buildings. Here, we’ll explain what needs to happen and which PV circuits are subject to this Code requirement, and discuss the methods and equipment available to achieve compliance. Additionally, we look forward to the upcoming 2017 NEC and how changes to the Code will impact rapid shutdown requirements.

Why is Rapid Shutdown (RSD) Needed?

Residential PV arrays are commonly installed with series string voltages up to 600 VDC (non-residential systems up to 1,000 VDC). A simple rooftop DC disconnect cannot protect emergency responders from these high voltages—during the day, full array voltage is produced on the conductors up to the input side of that disconnect. And on the output side of the DC disconnect, capacitors in the inverter can create high voltage between the DC disconnect and the inverter. Article 690.12 proposes solutions to rapidly reduce voltage to an acceptable level.

2014 NEC 690.12 Requirements

This NEC section is broken into five subsections. In 690.12(1), the NEC specifies which conductors must be controlled by a RSD method—PV system conductors of more than 5 feet in length inside a building, or more than 10 feet from a PV array. The 2014 NEC permits having a 10-foot zone around the PV array within which PV circuits on a building can still be at high voltage after shutdown is activated. This area will be reduced in the 2017 NEC as RSD requirements become more restrictive.

Sections 690.12 (2) and (3) specify that when RSD is activated, controlled conductors must be no more than 30 V (with a maximum power of 240 volt-amps) within 10 seconds. 30 V is considered the “touch-safe” voltage limit in wet environments. This voltage still allows for 24 V control circuits to be used, to allow RSD methods using contactors. Limited voltage and power is measured between any two current-carrying conductors and also between any conductor and ground.

Part 4 of 690.12 requires labels be provided, informing responders that the system is equipped with RSD, with instructions on how to initiate shutdown. Lastly, 690.12(5) specifies that equipment must be listed and identified, but not specifically for PV systems—off-the-shelf contactors, motorized switches, and shunt trip breakers can be used. This is another subsection that will be changing in the 2017 NEC. Under the 2014 NEC, installers can use any listed equipment to provide RSD, as long as it’s not installed in a way that could violate the product’s listing.


Comments (3)

Edward-Dijeau's picture

The problem is, to be at 30 volts or less, each solar panel must be an 18 volt Solar panel and must be under 240 watts in output from the roof to the inverter or solar charge controler to be exempt from this RSD rule. Most micro inverters, that have UL approval today, need over 30 volts to opperate and the output, if kept on the roof, becomes a nominal 240 volts and should be in electrical raceway. Even if the 240 volts is cut, the 36 volt or higher output is still up at the panel. The only safe way to bring down power without a raceway is to have 18 volt panels with each panel fed separatly down to any converter, inverter, charge controler with no backfeed from other solar panels. Using Double pole, double throw relays, one for each panel. with the common terminal points going one to positive and the other to negative and the normally open cantact termanals connected to the micro inverter and the normally closed contact terminals connected to a charge controler for a back up battery system all using 12 or 24 volt coils and control with control voltage comming through contacts from a Master Control Relay from the Utility incomming power on each phase, can you run a system that would not require a RSD. Most older PV systems could fry a Fireman, even with the PV diconect at thr meter turned off because the DC voltage is still present, on the roof, in open conductors under every panel. The industry wanted to sell their epecialty cables and connectors to fly by night, not licenced installers to instal with "Plug and Play" rather than have the "Solar Panel Junktion Box" fed with real flecable conduit requiring Licenced Inside Wiremen hired by C-10 Electrical Contractors. If all the wiring, on the roof, was in conduit or raceway from the Solar panel junktion Box all the way to the electrical invertes, disconects and Main Electrical panel, both AC and DC, there would be no need for the RDS instalation or retrofit.

randy dunton_2's picture

module level electronics need to be kept as simple as possible in order for cost & longevity to have a chance of succeeding. Furthermore proprietary systems will always lack future proof assurance; will parts be available 5-10 years down the road? Helios Focus has developed a simple module level rapid shutdown switch for module manufacturers, which can be cost effectively licensed and implemented to adhere to NEC 2017 rapid shutdown. This technology was developed in 2009 and since then tested in the Arizona desert heat.

Edward-Dijeau's picture

If the Solar panel Junction Box had an input cable that would not let any power "out" of the Solare Panel unless a 12 or 24 volt signal was detected at the input but would just shunt the panel to a closed loop circuit to protect the Solar Panel's Life expectancy, you would have a safe panel at any desired voltage. This would work for new panels with the built in system. However, if conected to older panels within the required footage BEFORE any micro inverter or series connection, retrofitting would cost as much in labor as the new panel instalation because you would need to run another series of wires to every panel, break apart existing connction to install the device, reconect all the wires and have a Master control relay and low voltage power sorce to fire them. There is also the problem of older code instaltions grandfathered in and when a property is sold, would the upgrade need to be made before the NEW owner took up residance? Would the old owner just chose ro remove the solar before sale rather than pay for a retrofit? If a residential Solar System does not have the upgrade and shut down, could a fire department refuse to go up on a roof and put out a fire on an older Solar systems even with the required AC disconect? I think the older 25 year life expectancy panels will be replaced at the end of life with more efficient, safer solar panel systems, but, like you said, the system developed in 2009 still hase not been made commercialy available because the 2017 codes have not forced the industry to become safer. It took 50 years before the "Grounding 3 wire" receptical replaced the 2 wire neutral grounded keyed receptical so how long will it take for Solar Panels to become safer?

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