Changes to the interconnection rules for solar PV systems in the NEC 2014
This week’s #SolarMOOC lecture covered changes to the National Electric Code interconnection rules (705.12). Richard Stovall, SolPowerPeople CEO and Instructor, reviewed how the 2014 code will differ from the 2011 code in the rules that govern how solar PV systems are connected to the grid supply at main distribution panels.
Richard reviews feeder taps, 100% rule, 120% rule and reveals that the NEC 2014 offers an improvement that allows more flexibility at the point of interconnection.
Utility Interconnection and the 120 Rule - In this previous lecture Richard reviews the 120% rule as it is outlined in the 2011 Code.
Article 705.12 - Here’s a snippet preview of the 2014 National Electric Code that is discussed in the lecture:
705.12Point of Connection.
The output of an interconnected electric power source shall be connected as specified in 705.12(A), (B), (C), or (D).
(A) Supply Side.
An electric power production source shall be permitted to be connected to the supply side of the service disconnecting means as permitted in 230.82(6). The sum of the ratings of all overcurrent devices connected to power production sources shall not exceed the rating of the service.
(B) Integrated Electrical Systems.
The outputs shall be permitted to be interconnected at a point or points elsewhere on the premises where the system qualifies as an integrated electrical system and incorporates protective equipment in accordance with all applicable sections of Article 685.
(C) Greater Than 100 kW.
The outputs shall be permitted to be interconnected at a point or points elsewhere on the premises where all of the following conditions are met:
- The aggregate of non-utility sources of electricity has a capacity in excess of 100 kW, or the service is above 1000 volts.
- The conditions of maintenance and supervision ensure that qualified persons service and operate the system.
- Safeguards, documented procedures, and protective equipment are established and maintained.
(D) Utility-Interactive Inverters.
The output of a utility-interactive inverter shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises. Where distribution equipment, including switchgear,^switchboards, or panelboards, is fed simultaneously by a primary source(s) of electricity and one or more utility-interactive inverters, and where this distribution equipment is capable of supplying multiple branch circuits or feeders, or both, the interconnecting provisions for the utilityinteractive inverter(s) shall comply with 705.12(D)(1) through (D)(6).
(1)Dedicated Overcurrent and Disconnect.
The source interconnection of one or more inverters installed in one system^ shall be made at a dedicated circuit breaker or fusible disconnecting means.
(2)Bus or Conductor Ampere Rating.
One hundred twenty-five percent of the inverter output circuit current shall be used in ampacity calculations for the following:^
- Feeders. Where the inverter output connection is made to a feeder at a location other than the opposite end of the feeder from the primary source overcurrent device, that portion of the feeder on the load side of the inverter output connection shall be protected by one of the following:^Taps.In systems where inverter output connections are made at feeders, any taps shall be sized based on the sum of 125 percent of the inverter(s) output circuit current and the rating of the overcurrent device protecting the feeder conductors as calculated in 240.21(B).^
- The feeder ampacity shall be not less than the sum of the primary source overcurrent device and 125 percent of the inverter output circuit current.
- An overcurrent device on the load side of the inverter connection shall be rated not greater than the ampacity of the feeder.
- Busbars. One of the methods that follows shall be used to determine the ratings of busbars in panelboards.
The sum of 125 percent of the inverter(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.
Informational Note: This general rule assumes no limitation in the number of the loads or sources applied to busbars or their locations.^
Where two sources, one a utility and the other an inverter, are located at opposite ends of a busbar that contains loads, the sum of 125 percent of the inverter(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed 120 percent of the ampacity of the busbar. The busbar shall be sized for the loads connected in accordance with Article 220. A permanent warning label shall be applied to the distribution equipment adjacent to the back-fed breaker from the inverter that displays the following or equivalent wording:^
INVERTER OUTPUT CONNECTION;
DO NOT RELOCATE THIS OVERCURRENT DEVICE.
The warning sign(s) or label (s) shall comply with110.21(B).^
The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar. The rating of the overcurrent device protecting the busbar shall not exceed the rating of the busbar. Permanent warning labels shall be applied to distribution equipment that displays the following or equivalent wording:
THIS EQUIPMENT FED BY MULTIPLE SOURCES.
TOTAL RATING OF ALL OVERCURRENT DEVICES,
EXCLUDING MAIN SUPPLY OVERCURRENT
SHALL NOT EXCEED AMPACITY OF BUSBAR.
The warning sign(s) or label (s) shall comply with110.21(B).^
Connections shall be permitted on multiple-ampacity busbars or center-fed panelboards where designed under engineering supervision that includes fault studies and busbar load calculations.^
Equipment containing overcurrent devices in circuits supplying power to a busbar or conductor supplied from multiple sources shall be marked to indicate the presence of all sources.
(4)Suitable for Backfeed.
Circuit breakers, if backfed, shall be suitable for such operation.
Informational Note: Fused disconnects, unless otherwise marked, are suitable for backfeeding.^
Listed plug-in-type circuit breakers backfed from utility-interactive inverters that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.
(6)Wire Harness and Exposed Cable Arc-Fault Protection.
A utility-interactive inverter(s) that has a wire harness or cable output circuit rated 240 V, 30 amperes, or less, that is not installed within an enclosed raceway, shall be provided with listed ac AFCI protection.^