Combiner Boxes

      According to the National Electric Code, section 690.15, PV arrays must have a disconnecting means to isolate the inverter from the PV power source. Grid-tie inverters that utilize PV arrays with voltages above 250VDC require a disconnect rated for 600VDC to perform this function.

      The Square-D 600 VDC 30 amp 3-pole safety switches are UL listed to handle 13A at 600VDC per pole. They can be used for disconnecting up to three PV arrays for three grid-tie inverters. It has wiring lugs that are rated to accept two #14 to #10 wires in each lug. This allows the disconnect switch to also act as a string combiner in systems that utilize two strings of PV modules per inverter. All other Square D 600 VDC disconnects are rated for disconnecting one string at full rated power.

      Many utilities require an AC disconnect between an intertie inverter and the AC load center, close to the AC service entrance, with a visible and lockable handle. A 30 amp 240 volt disconnect is good for up to 5kW at 240 VAC (one or two 2500W intertie inverters) and the 60 amp disconnect is good for up to 12.5kW (three to five 2500W intertie inverters). For connection of multiple inverters to one of these disconnects, use an AC load center, with a circuit breaker for each inverter installed, as an AC combiner box between the inverters and the disconnect switch. The breakers can be back-fed with the inverter outputs and the load center main lugs will handle the combined outputs to be connected to the AC disconnect.

      Use Class-R fuses of the proper amperage for fused disconnects. Disconnects are rain-tight (NEMA 3R) for outdoor use. Order the neutral bus bar and ground bus bar if you need to land these conductors in the disconnect switch box.