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Thread: NEC 2008, Art 690.64(B)(1)

  1. #1
    Join Date
    Feb 2007

    NEC 2008, Art 690.64(B)(1)

    I've run into a little issue here and could use some assistance. We have a Utility Grade PV project going on-line soon, and I'm having a disagreement with the installer/designer that their installation violates the NEC 2008 Art. 690.64(B)(1) interpretation. According to the installer, they feel the intent of the code is met with their installation (refer to diagram and my comments). They show two inverters tied to a step down transformer with one fused disconnect switch vs. two separate dedicated over current devices per inverter as required per the NEC. The 2008 handbook goes on to say that the outputs of utility interactive inverters may not be connected directly in parallel without first being connected to the required dedicated circuit breaker or fusible disconnecting means. As an FYI, each inverter has an internal OCP.

    Just wondering if NEC Code allows this type of connection as shown on the diagram for Utility Interactive Inverters (Grid tie PV). The installer told me that a UL listing may be granted on the entire "SKID" assembly at some point (includes two inverters and the transformer along with all AC connections), but in the meantime how do I handle the code interpretation? Is this indeed a code violation? Two concerns I have: (1) how the utility will clear a fault if it occurs on the seconday cable between the transformer and the Inverter, and (2) should the secondary cable be sized to support the current that the primary fuse would allow?

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