SOLAR DC DISCONNECT SWITCH

                                                                                                                  Photo courtesy of Explorist.life

A Solar DC (Direct Current) Disconnect Switch, aka Solar DC Isolator, is a device that simultaneously disconnect the solar array wires (Strings) from the solar charge controller. However, it does not need to provide overcurrent protection. The DC disconnect should not be confused with an AC disconnect; the two are not interchangeable, due to differences in their Sine Waves.

According to the U.S. National Electric Code (NEC) 2020 Article 690.13 a “means shall be provided to disconnect the PV system from all wiring systems including power systems, energy storage systems, and utilization equipment and its associated premises wiring”. According to British Standard (BS) 7671:2018, Section 712.537.2.2.101 “A switch disconnector or a circuit breaker suitable for isolation shall be provided on the DC side of the inverter.”

Some solar DC disconnect comes with preinstalled male / female MC-4 connectors which are convenient if the entire solar PV disconnect needs to be serviced or replaced. However, the MC-4 connectors should not serve as the primary means of solar DC disconnection. Also, it is recommended that the preinstalled MC-4 connectors on the solar PV disconnect are the same brand and model used on the PV array wires to prevent any potential of incompatibility or equipment failure.

A solar DC disconnect should not be confused with a solar DC breaker; the latter provides overcurrent protection. The solar DC disconnect pictured below supports 2 sets / strings of PV wires from 2 separate PV arrays and provides “simultaneous” disconnection of both PV arrays. The ends of the 10 AWG PV wires should be prepared with heat-shrink and ferrules then perforate a M25 entry gland and inserted in to their respective terminals. The M25 gland maintains the IP66 sealing effectiveness rating of the electrical enclosure. The disconnect terminals do not have a specific polarity but the polarity of the inserted PV wires should match the polarity of their corresponding counterpart—positive to positive, negative to negative. The energized PV wires will enter the DC disconnect from the top of the DC disconnect while the non-energized wires will exit from the bottom; then transition to the MPPT Solar Charge Controller.

                                                                                                                            Photo courtesy of Explorist.Life

CAUTION: If the PV wires are connected to the solar array they may be energized and should be disconnected from the array before maintenance. Also, for added protection, some solar DC disconnection switch models have lock-out features to prevent accidental activation during maintenance.

                                                                     Photo courtesy of Solar PV

The solar DC disconnect will be rapidly accessible in the Tiny Off-Grid House Engineering Compartment. The manually operated switch clearly indicates if the switch is in the ON or OFF positions (2023 NEC 690.17(C); along with proper signage indicating its intended purpose (2023 NEC 690.56(B).

For more information on “Sizing & Wiring An Off-Grid Solar Array” please read OFF-GRID SOLAR

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