More 2014 Code Changes: Page 2 of 2

Intermediate
Cable tray for PV
New allowances in Article 690 make it easier to use cable tray for PV source- and output-circuit wire management.
Microinverter systems
Due to the amount of exposed AC conductors typical of most AC module and microinverter systems, AC arc-fault protection is now required.
A partition is now required between AC and DC conductors
A partition is now required between AC and DC conductors, even if connected to the same inverter (such as in the gutter box shown here).
Cable tray for PV
Microinverter systems
A partition is now required between AC and DC conductors

Battery Disconnects & OCPDs

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.

Section 705.12(D)

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:

  • 125% of the inverter’s rated current + the rating of the OCPD protecting the busbar ≤ the busbar rating. The location of the back-fed inverter breaker is not stated, and the “120% rule” is not being applied.
  • 125% of the inverter’s rated current + the rating of the OCPD protecting the busbar ≤ 120% of the busbar rating.The breakers must be at opposite ends of the busbar so that current from the two sources will not be additive at any point on the busbar, in the same manner that the “120% rule” was applied in the 2011 NEC.
  • The sum of the ratings of all the overcurrent protection devices, both supply and load, but excluding the rating of the overcurrent device protecting the busbar from the utility supply ≤ busbar rating. This allowance is for inverter AC combiner subpanels, in which the output of multiple inverters are connected and run through a single, larger OCPD to the point of interconnection. By counting both supply and load breakers, this section makes provisions for load circuits such as data monitoring, security systems, or other associated loads to be fed from a panel being used to combine the output of multiple inverters. Note that in this option the calculation is based on the inverter’s back-fed breaker size, not 125% of the inverter’s rated current. The combination of supply and load breakers being less than the rating of the busbar ensures that it cannot be subject to overcurrent. This will allow smaller subpanels, since the OCPD protecting the busbar from the utility source is not counted.
  • Engineering studies, including busbar loading and fault studies, can be performed for center-fed panel boards or load centers with multiple-ampacity busbars. Although center-fed panels are common in some areas of the country, there was previously no guidance for making load side connections to them. Under the 2011 NEC, the sum of all supply breakers had to be less than the busbar’s rating (inverter breaker(s) + OCPD protecting the busbar from the utility supply, no allowance for the 120% rule, since the “opposite” end of the busbar from the utility supply OCPD could not be defined), effectively limiting the size of PV system that could be connected to this equipment.

Other Changes

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).

Access

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.

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