Rapid Shutdown – Safety First

Although not mandated by federal law, the National Electric Code (NEC) has been adopted by many state and local authorities responsible for building and construction safety. With over a century of history, the NEC is routinely updated to keep up with technology and suggest best practices.

For example, starting in 2019, the NEC recommends new guidelines that reflect the changing adoption of solar design, where systems implemented with microinverters and with string inverters with power optimizers require new safety procedures.

In its most basic form, Rapid Shutdown refers to designs and installation procedures that allow the solar power generation source to be isolated quickly from the circuit. Solar panels must be disconnected in order to reduce or eliminate shock hazards in emergency situations. The photovoltaic reaction in solar panels continues as long as the front surface is exposed to light. The more potent the exposure, the more solar power is produced. Rapid shutdown breaks the circuit, indirectly “turning off” the panels from a point downstream in the power circuit. The panels themselves are still electrically “hot”.

Perhaps most importantly, these protocols are key to keeping a grid-connected solar energy system safe in the event of a grid power outage. Whether a person intervenes to purposefully cause a shutdown or the reaction is automatic due to grid faults, the designed response is the same.

Code Compliance – Design Matters

Just as solar power inverters must be selected to match the design and installation configuration, so are rapid disconnect solutions dependent on actual conditions. Disconnecting a single solar panel from a power circuit is very different from disconnecting at once 25 panels in a chain or string.

In a way, it’s analogous to stopping a economy car compared to stopping an over the road truck, or for large systems perhaps a traveling freight train. The power at the point of disconnect is key.

The newest 2019 NEC revision recommends module-level shutdown, meaning a disconnect as close as possible to the solar panels. With the growing use of power optimizers and microinverters, this requires robust communication from those components back to the main system disconnect, or breaker.

When that main breaker is tripped or shut off, each panel level optimizer or microinverter must respond and disconnect.

In technical terms, after 30 seconds no person near a solar panel should be subjected to a hazardous voltage, as defined by the NEC. Nearest the power generation (solar panels) that is 80 volts, and beyond 3 feet that is 30 volts.

Manufacturers Compliance

The good news is that manufacturers of solar power management components now build NEC Rapid Shutdown compliant devices. Power optimizers and inverters, microinverters, and AC disconnects are all designed to communicate following a shared protocol and to meet NEC standards.

See more about our product selection for rapid shutdown below:

Enphase Rapid Shutdown System

Enphase Energy is a leader in solar microinverter design and manufacturing. These products have been developed to meet the earliest Rapid Shutdown requirements in past years.

SolarEdge Optimizer Rapid Shutdown System

SolarEdge has been manufacturing and shipping string inverters and power optimizers for over a decade. With a focus on continuous improvement, the California-based company has provided rapid shutdown compliant power optimizers in conjunction with the fast adoption of NEC guidelines by state and local agencies.

Tigo TS4 Rapid Shutdown System

Tigo is a Silicon Valley company founded in 2007 by a team of experienced solar technologists. The second generation TS4 universal platform was designed for the widest array of solar energy system needs. With a number of power monitoring and power management options, the product line will meet all Massachusetts and Rhode Island rapid shutdown requirements.