Some installers are called upon to upgrade older, grounded, transformer-based inverters with newer, ungrounded, transformer-less, inverters. The general process for upgrading these systems is straight forward and outlined below.
- Check the existing PV wire (typically USE-2/RWH-2) for any defects, kinks, or damage. If the wire is still in good shape, you are allowed by NEC 2017 to repurpose this for a retrofit system.
- Identify the grounded PV wire. It may be colored white. Ensure to re-identify this as a ungrounded conductor with proper wire labeling or by covering up/removing any white markings that are on the wire.
- Install a new DC disconnect which opens both poles (positive and negative) of the PV array. Luckily, most transformer-less, non-isolated, inverters are now equipped with a DC disconnect integrated into the inverter itself. If you need a DC disconnect, a Square-D HU361 will work as well.