ARTICLE 705

Interconnected Electric Power Production Sources

Part I. General

Scope. This article covers installation of one or more electric power production sources operating in parallel with a primary source(s) of electricity.Informational Note: Examples of the types of primary sources include a utility supply or an on-site electric power source(s).
Definitions.Interactive Inverter Output Circuit. The conductors between the interactive inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.Microgrid System. A premises wiring system that has genera‐ tion, energy storage, and load(s), or any combination thereof,Microgrid Interconnect Device (MID). A device that allows a microgrid system to separate from and reconnect to a primary power source.
that includes the ability to disconnect from and parallel with the primary source.
Informational Note: The application of Article 705 to microgridsystems is limited by the exclusions in 90.2(B)(5) related to elec‐ tric utilities.Multimode Inverter. Equipment having the capabilities of both the interactive inverter and the stand-alone inverter.Power Production Equipment. The generating source, and all distribution equipment associated with it, that generates elec‐ tricity from a source other than a utility supplied service.Informational Note: Examples of power production equipment include such items as generators, solar photovoltaic systems, and fuel cell systems.
Other Articles. Interconnected electric power produc‐ tion sources shall comply with this article and also with the applicable requirements of the articles in Table 705.3.

705.6 Equipment Approval. All equipment shall be approved for the intended use. Interactive inverters for interconnection to systems interactive equipment intended to operate in paral‐ lel with the electric power system including, but not limited to, interactive inverters, engine generators, energy storage equip‐ ment, and wind turbines shall be listed and or field labeled for the intended use of interconnection service.

705.8 System Installation. Installation of one or more electri‐ cal power production sources operating in parallel with a primary source(s) of electricity shall be performed only by qualified persons.

Informational Note: See Article 100 for the definition of Quali‐ fied Person.

705.10 Directory. A permanent plaque or directory denoting the location of all electric power source disconnecting means on or in the premises shall be installed at each service equip‐ ment location and at the location(s) of the system discon‐ nect(s) for all electric power production sources capable of being interconnected. The marking shall comply with

110.21(B).

Exception: Installations with large numbers of power production sour‐ ces shall be permitted to be designated by groups.

or (B).

705.12 Point of Connection. The output of an interconnec‐ ted electric power source shall be connected as specified in 705.12(A)

Table 705.3 Other Articles

Equipment/System Article

Generators 445

Solar photovoltaic systems 690

Fuel cell systems 692

Wind electric systems 694

Emergency systems 700

Legally required standby systems 701

Optional standby systems 702

Energy storage systems 706

Stand-alone systems 710

DC microgrids 712

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.•
Load Side. The output of an interconnected electricpower source 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 distribu‐ tion equipment, including switchgear, switchboards, or panel‐ boards, is fed simultaneously by a primary source(s) of electricity and one or more other power source(s), and where this distribution equipment is capable of supplying multiple branch circuits or feeders, or both, the interconnecting provi‐ sions for other power sources shall comply with 705.12(B)(1) through (B)(5).
1. Dedicated Overcurrent and Disconnect. Each source interconnection of one or more power sources 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 power source output circuit current shall be used in ampacity calculations for the following:

Feeders. Where the power source 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 power source output connection shall be protected by one of the following:
1. The feeder ampacity shall be not less than the sum of the primary source overcurrent device and125 percent of the power source output circuit current.
2. An overcurrent device on the load side of the power source connection shall be rated not greater than the ampacity of the feeder.
Taps. In systems where power source output connections are made at feeders, any taps shall be sized based on the sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protect‐ ing the feeder conductors as calculated in 240.21(B).
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 power source(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 primary power source and the other another power source, are located at opposite ends of a busbar that contains loads, the sum of 125 percent of the power source(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 power source that displays the following or equivalent wording:WARNING:POWER SOURCE OUTPUT CONNECTION — DO NOT RELOCATE THIS OVERCURRENT DEVICE.The warning sign(s) or label(s) shall comply with 110.21(B).
The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, exclud‐ ing 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 displaying the following or equiva‐ lent wording:WARNING:THIS EQUIPMENT FED BY MULTIPLE SOURCES. TOTAL RATING OF ALL OVERCURRENT DEVICES EXCLUDING MAIN SUPPLY OVERCURRENT DEVICE SHALL NOT EXCEED AMPACITY OF BUSBAR.The warning sign(s) or label(s) shall comply with 110.21(B).
A connection at either end, but not both ends, of a center-fed panelboard in dwellings shall be permitted where the sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar does not exceed 120 percent of the current rating of the busbar.
Connections shall be permitted on multiple-ampacity busbars where designed under engineering supervision that includes available fault current and busbar load calculations.

Marking. 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.
Suitable for Backfeed. Circuit breakers, if backfed, shall be suitable for such operation.Informational Note: Fused disconnects, unless otherwise marked, are suitable for backfeeding.
Fastening. Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.

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705.14 Output Characteristics. The output of a generator or

other electric power production source operating in parallel with an electrical supply system shall be compatible with the voltage, wave shape, and frequency of the system to which it is connected.

Informational Note: The term compatible does not necessarily mean matching the primary source wave shape.

705.16 Interrupting and Short-Circuit Current Rating. Consideration shall be given to the contribution of fault currents from all interconnected power sources for the inter‐ rupting and short-circuit current ratings of equipment on inter‐ active systems.

Disconnecting Means, Sources. Means shall be provi‐ ded to disconnect all ungrounded conductors of an electric power production source(s) from all other conductors.
Disconnecting Means, Equipment. Means shall be provided to disconnect power production equipment, such as interactive inverters or transformers associated with a power production source, from all ungrounded conductors of all
sources of supply. Equipment intended to be operated and maintained as an integral part of a power production source exceeding 1000 volts shall not be required to have a discon‐ necting means.
Disconnect Device. The disconnecting means for ungrounded conductors shall consist of a manual or power operated switch(es) or circuit breaker(s) that complies with the following:

Located where readily accessible
Externally operable without exposing the operator to contact with live parts and, if power operated, of a type that is opened by hand in the event of a power-supply fail‐ ureInformational Note: This overcurrent protection protects against short-circuit current supplied from the primary source(s) of electricity.Exception: Where the overcurrent protection for the power production source is located more than 3 m (10 ft) from the point of connection for the electric power production source to the service, cable limiters or current-limited circuit breakers for each ungrounded conductor shall be installed at the point where the electric power production conductors are connected to the service.705.32 Ground-Fault Protection. Where ground-fault protec‐ tion is used, the output of an interactive system shall be connected to the supply side of the ground-fault protection.Exception: Connection shall be permitted to be made to the load side ofindicate
Plainlypositionwhether in the open (off) or closed (on)ground-fault protection, if there is ground-fault protection for equip‐ ment from all ground-fault current sources.
Have ratings sufficient for the maximum circuit current,available short-circuit current, and voltage that is available at the terminals
Where the line and load terminals are capable of being energized in the open position, marked in accordance with the warning in 690.13(B)Informational Note : In parallel generation systems, some equip‐ ment, including knife blade switches and fuses, is likely to be energized from both directions. See 240.40.
Simultaneously disconnect all ungrounded conductors of the circuit
Be lockable in the open (off) position in accordance with 110.25

705.23 Interactive System Disconnecting Means. A readily accessible means shall be provided to disconnect the interactive system from all wiring systems including power systems, energy storage systems, and utilization equipment and its associated premises wiring.

Overcurrent Protection. Conductors shall be protec‐ ted in accordance with Article 240. Equipment and conductors connected to more than one electrical source shall have a suffi‐ cient number of overcurrent devices located so as to provide protection from all sources.
1. Solar Photovoltaic Systems. Solar photovoltaic systems shall be protected in accordance with Article 690.
2. Transformers. Overcurrent protection for a transformer with a source(s) on each side shall be provided in accordance with 450.3 by considering first one side of the transformer, then the other side of the transformer, as the primary.
3. Fuel Cell Systems. Fuel cell systems shall be protected in accordance with Article 692.
4. Interactive Inverters. Interactive inverters shall be protec‐ ted in accordance with 705.65.
5. Generators. Generators shall be protected in accordance with 705.130.
Location of Overcurrent Protection. Overcurrent protection for electric power production source conductors, connected to the supply side of the service disconnecting means in accordance with 705.12(A), shall be located within 3 m (10 ft) of the point where the electric power production source conductors are connected to the service.

705.40 Loss of Primary Source. Upon loss of primary source, an electric power production source shall be automatically disconnected from all ungrounded conductors of the primary source and shall not be reconnected until the primary source is restored.

Exception: A listed interactive inverter shall be permitted to automati‐ cally cease exporting power upon loss of primary source and shall not be required to automatically disconnect all ungrounded conductors from the primary source. A listed interactive inverter shall be permitted to automatically or manually resume exporting power to the utility once the primary source is restored.

Informational Note No. 1: Risks to personnel and equipment associated with the primary source could occur if an utility inter‐ active electric power production source can operate as an inten‐ tional island. Special detection methods are required to determine that a primary source supply system outage has occur‐ red and whether there should be automatic disconnection. When the primary source supply system is restored, special detection methods can be required to limit exposure of power production sources to out-of-phase reconnection.

Informational Note No. 2: Induction-generating equipment on systems with significant capacitance can become self-excited upon loss of the primary source and experience severe overvolt‐ age as a result.

An interactive inverter shall be permitted to operate as a stand-alone system to supply loads that have been disconnected from electrical production and distribution network sources.

705.42 Loss of 3-Phase Primary Source. A 3-phase electric power production source shall be automatically disconnected from all ungrounded conductors of the interconnected systems when one of the phases of that source opens. This requirement shall not be applicable to an electric power production source providing power for an emergency or legally required standby system.

Exception: A listed interactive inverter shall be permitted to automati‐ cally cease exporting power when one of the phases of the source opens and shall not be required to automatically disconnect all ungrounded conductors from the primary source. A listed interactive inverter shall be permitted to automatically or manually resume exporting power to the utility once all phases of the source are restored.

705.50 Grounding. Interconnected electric power production sources shall be grounded in accordance with Article 250.

Exception: For direct-current systems connected through an inverter directly to a grounded service, other methods that accomplish equivalent system protection and that utilize equipment listed and identified for the use shall be permitted.

Part II. Interactive Inverters

705.60 Circuit Sizing and Current.

Calculation of Maximum Circuit Current. The maximum current for the specific circuit shall be calculated in accordance with 705.60(A)(1) and (A)(2).
1. Inverter Input Circuit Currents. The maximum current shall be the maximum rated input current of the inverter.
2. Inverter Output Circuit Current. The maximum current shall be the inverter continuous output current rating.
Ampacity and Overcurrent Device Ratings. Inverter system currents shall be considered to be continuous. The circuit conductors and overcurrent devices shall be sized to carry not less than 125 percent of the maximum currents as calculated in 705.60(A). The rating or setting of overcurrent devices shall be permitted in accordance with 240.4(B) and (C).

Exception: Circuits containing an assembly together with its overcurrent device(s) that is listed for continuous operation at 100 percent of its rating shall be permitted to be utilized at 100 percent of its rating.

705.65 Overcurrent Protection.

Circuits and Equipment. Inverter input circuits, inverter output circuits, and storage battery circuit conductors and equipment shall be protected in accordance with the require‐ ments of Article 240. Circuits connected to more than one elec‐ trical source shall have overcurrent devices located so as to provide overcurrent protection from all sources.Exception: An overcurrent device shall not be required for circuit conductors sized in accordance with 705.60(B) and located where one of the following applies:
1. There are no external sources such as parallel-connected source circuits, batteries, or backfeed from inverters.
2. The short-circuit currents from all sources do not exceed the ampacity of the conductors.
Informational Note: Possible backfeed of current from any source of supply, including a supply through an inverter into the inverter output circuit and inverter source circuits, is a consider‐ ation in determining whether adequate overcurrent protection from all sources is provided for conductors and modules.
Power Transformers. Overcurrent protection for a trans‐ former with a source(s) on each side shall be provided in accordance with 450.3 by considering first one side of the trans‐ former, then the other side of the transformer, as the primary.Exception: A power transformer with a current rating on the side connected toward the interactive inverter output that is not less than the rated continuous output current of the inverter shall be permitted with‐ out overcurrent protection from that source.
Conductor Ampacity. Power source output circuit conductors that are connected to a feeder, if smaller than the feeder conductors, shall be sized to carry not less than the larger of the current as calculated in 705.60(B) or as calculated in accordance with 240.21(B) based on the over-current device protecting the feeder.

705.70 Interactive Inverters Mounted in Not Readily Accessi‐ ble Locations. Interactive inverters shall be permitted to be mounted on roofs or other exterior areas that are not readily accessible. These installations shall comply with (1) through (4):

A dc disconnecting means shall be mounted within sight of or in the inverter.
An ac disconnecting means shall be mounted within sight of or in the inverter.
An additional ac disconnecting means for the inverter shall comply with 705.22.
A plaque shall be installed in accordance with 705.10.

705.80 Utility-Interactive Power Systems Employing Energy Storage. Utility-interactive power systems employing energy storage shall also be marked with the maximum operating volt‐ age, including any equalization voltage, and the polarity of the grounded circuit conductor.

705.82 Hybrid Systems. Hybrid systems shall be permitted to be interconnected with interactive inverters.

705.95 Ampacity of Neutral Conductor. The ampacity of the neutral conductors shall comply with either (A) or (B).

Neutral Conductor for Single Phase, 2-Wire Inverter Output. If a single-phase, 2-wire inverter output is connected to the neutral and one ungrounded conductor (only) of a 3-wire system or of a 3-phase, 4-wire, wye-connected system, the maximum load connected between the neutral and any one ungrounded conductor plus the inverter output rating shall not exceed the ampacity of the neutral conductor.
Neutral Conductor for Instrumentation, Voltage, Detection or Phase Detection. A conductor used solely for instrumenta‐ tion, voltage detection, or phase detection and connected to a single-phase or 3-phase interactive inverter, shall be permitted to be sized at less than the ampacity of the other current- carrying conductors and shall be sized equal to or larger than the equipment grounding conductor.

705.100 Unbalanced Interconnections.

Single Phase. Single-phase inverters for hybrid systems and ac modules in interactive hybrid systems shall be connec‐ ted to 3-phase power systems in order to limit unbalanced voltages to not more than 3 percent.Informational Note: For interactive single-phase inverters, unbalanced voltages can be minimized by the same methods that are used for single-phase loads on a 3-phase power system. See ANSI/C84.1-2011, Electric Power Systems and Equipment — Volt‐ age Ratings (60 Hertz).
Three Phase. Three-phase inverters and 3-phase ac modules in interactive systems shall have all phases automati‐ cally de-energized upon loss of, or unbalanced, voltage in one or more phases unless the interconnected system is designed so that significant unbalanced voltages will not result.

Part III. Generators

705.130 Overcurrent Protection. Conductors shall be protec‐ ted in accordance with Article 240. Equipment and conductors connected to more than one electrical source shall have over‐ current devices located so as to provide protection from all sources. Generators shall be protected in accordance with 445.12.

705.143 Synchronous Generators. Synchronous generators in a parallel system shall be provided with the necessary equip‐ ment to establish and maintain a synchronous condition.

Part IV. Microgrid Systems

705.150 System Operation. Microgrid systems shall be permit‐ ted to disconnect from the primary source of power or other interconnected electric power production sources and operate as a separate microgrid system.

705.160 Primary Power Source Connection. Connections to primary power sources that are external to the microgrid system shall comply with the requirements of 705.12.

705.165 Reconnection to Primary Power Source. Microgrid systems that reconnect to primary power sources shall be provi‐ ded with the necessary equipment to establish a synchronous transition.

705.170 Microgrid Interconnect Devices (MID). Microgrid interconnect devices shall comply with the following:

Be required for any connection between a microgrid system and a primary power source
Be listed or field labeled for the application
Have sufficient number of overcurrent devices located to provide overcurrent protection from all sources

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