Friends:
I recently studied the implications of replacing a negative grounded grid-interactive inverter with transformerless inverter or inverters. I had noticed language in 690.9(C)Informational note that indicates only the positive PV lead needs to be disconnected. August Goers kindly forwarded to me an article by Bill Brooks that explored this subject and other changes in the 2017 NEC regarding PV systems. Here is a link <https://millersolar.com/MillerSolar/Resources/NEC/2017_NEC_changes.pdf> to that article. Now I want to learn how to apply this information to stand-alone systems. I asked one of the local AHJs about this and they appeared to have no awareness of any change in bonding requirements. I offered my preliminary opinion (see below) and they immediately adopted it as policy! Are those of you installing off-grid now disconnecting positive and negative? Here is my take on the subject: For stand-alone systems: For ground mount systems with not more than two source circuits, ground fault protection is not required (690.41(B) Exception). This means the negative lead can be solidly grounded. In such cases only the positive lead needs to be switched. For all other systems ground-fault protection is required. To provide ground fault protection, the negative cannot be solidly grounded. Therefore the positive and negative leads must be disconnected at the appropriately located disconnecting means (690.9(C) Informational note). Onto the subject of battery disconnects: I am probably behind the times on this one too. Are you providing externally accessible battery system disconnects? Thanks in advance for any input on these questions. William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985
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