I read with interest Ryan Mayfield’s “Code Corner” article in HP157 about AC modules, and their unique treatment in the NEC. Enphase has just released its M250 microinverter, which has built-in, isolated DC grounding. Enphase claims this eliminates the requirement for a grounding electrode conductor (GEC).
Does this development signal a departure for future grounding requirements? Can this technology allow “any” module to be retrofit and then treated as a “factory” AC module?
Jody Herperger • Regina, Saskatchewan
This release from Enphase will undoubtedly change the method for grounding its new inverters, but will not change overall module-grounding requirements.
An inverter and module must be factory-supplied and listed as an AC module to qualify for that distinction. Attaching an Enphase M250 microinverter to a PV module doesn’t qualify. Code still considers this setup two distinct pieces of equipment—and your installation will need to reflect that.
However, the new Enphase microinverter eliminates the need for a GEC between microinverters. The array and inverters still need proper bonding via an equipment-grounding conductor (EGC) but per Enphase instructions, a GEC is not required. The sizing and installation requirements surrounding an EGC are not as stringent as they are for the GEC, so this will likely result in installation-labor savings. The availability of an EGC in the cable system will play a big role in the installation. For example, Enphase microinverters contain an EGC in their cabling system, so bonding modules and inverters to the rack establishes the required bond. The cable system can carry that from the roof.
As with all grounding issues, this is not a slam dunk. There are varying opinions on this subject, so check with your authority having jurisdiction to make sure they agree with the manufacturer and your installation plans.
Ryan Mayfield • PV Systems Technical Editor, SolarPro magazine