Section 690.71(H) has new requirements for disconnects and overcurrent protection for systems with batteries or other energy-storage devices. When the output conductors connected to the battery (or energy-storage device) are longer than 5 feet, or pass through a wall or partition, there must be a disconnect and overcurrent protection (breaker or fused disconnect) at the battery, on the ungrounded conductor. The battery must connect to the “line” side terminals of a fused disconnect. Disconnects and OCPDs cannot be installed in an area where explosion is possible (for instance, in a battery box with vented lead-acid batteries). If the battery disconnect is not visible and within 50 feet of the connected equipment (inverter and charge controller) then another disconnect is required at the equipment (for example, at the inverter). When the PV system AC and DC disconnects are not within sight of the battery disconnect, directories (descriptive text and a diagram is ideal) showing the location of all disconnects are required on each disconnect. This ensures that all sources of power are identified and can be isolated.
The most significant changes in Article 705 are in 705.12(D), which further clarifies the ways a PV system can be connected on the load side of the AC service disconnecting means, particularly 705.12(D)(2), “Bus or Conductor Ampere Rating.” Under earlier editions of the Code, busbar calculations were performed using the rating of the overcurrent protection devices (OCPDs) that were supplying power to the busbar (the main, or supply breaker, plus any back-fed breakers connected to grid-tied inverters).
One significant change is that 125% of the inverter’s rated AC output current, rather than the actual back-fed breaker size, is used for busbar calculations. The advantage is that the installed OCPD size is usually larger than the calculated minimum OCPD size (since, if the calculation doesn’t result in a standard size, it has to be rounded up), but 125% of the inverters’ rated output current (typically a smaller value than the installed OCPD size) can be used in busbar calculations, potentially allowing larger PV systems to be interconnected on the load side of a service.
For example, consider a 7 kW, 240 VAC inverter with a rated output current of 29.2 A. The minimum breaker size, as well as the value for busbar calculations, is 36.5 A; the interconnection breaker would be 40 A, as it is the next larger standard size above the calculated minimum—but the 36.5 A will be used to ensure that the sources supplying current to the busbar don’t exceed 120% of the busbar’s rating.
Further clarification on busbar calculations is provided in 705.12(D)(2)(3), with four options:
Article 705 includes a requirement for AC arc-fault protection for utility-interactive inverters with wiring harnesses rated at 240 VAC and 30 A or less, unless the harnesses are installed within an enclosed raceway. This requirement—in 705.12(D)(6)—is aimed at microinverters and AC modules.
Section 705.31 stipulates that overcurrent protection for supply-side interconnections must be located within 10 feet of the point of interconnection, unless cable limiters (devices that isolate conductors from short circuits, but don’t necessarily provide overcurrent protection) or current-limited circuit breakers are installed. This helps reduce the risk from fault current sourced from the primary electricity source (the utility).
Brian Mehalic is a NABCEP-certified PV professional and ISPQ-certified PV instructor. He has experience designing, installing, servicing, and inspecting all types and sizes of PV systems. He is a curriculum developer and instructor for Solar Energy International.