Installing Microinverters

The M190 Enphase microinverters were in high demand and short supply, and my vision of a “barn-raising” installation—with half a dozen friends, taking a day or so to finish—turned into a piecemeal approach while I waited for the inverters to arrive.

I began at the bottom right of the lowest rack, wired the female cable end into the roof-mounted junction box, and then mounted the first inverter. I had planned to daisy-chain the AC cables up three rows, left one module, and then down three rows until I had placed all 15 microinverters. But when I installed the second inverter in the row above the first, I found that the AC cable built into the inverter was not long enough. Oops.

I called Enphase tech support and asked the technician to look at my blog posting photos so he could see the racking layout and understand my problem. He immediately offered to send me some 6-foot-long extension cables—free. I asked for four cables, anticipating changing the wiring sequence to start at bottom right, go left for five modules, then up one module, right five modules, then up one, then left five. Using this approach, I would only need to go up twice per block of inverters. Enphase later lengthened the cables an additional 8 inches to address this issue.

Enphase’s earlier model M175 had AC cables with male and female ends; my M190 microinverters have a male cable and a female connector built into the unit. I think the two-cable design was better as it allowed more flexibility in installation.

I mounted the inverters with an extra-large washer, regular washer, lock washer, and nut over the right mounting slot. The large washer covers the WEEB grounding washer between the inverter flange and the mounting rail to ensure it gets even pressure. I used a torque wrench to tighten the nuts to 10 foot-pounds, per the Wiley Electronics’ documentation for Iron Ridge mounting rails.

Enphase provides a chart that you use to indicate which inverter goes where so that their Enlighten Web interface can locate them. I removed one of the two bar-coded serial numbers that are stuck to each unit and stuck it onto the chart in the correct placement. This chart gets faxed to Enphase so that they can build the Web data page and validate the installation.

Enphase microinverters bolt easily to the PV mounting rails. They must be mounted under the modules to prevent interference with the module frame and mounting clips.