SOLAR PHOTOVOLTAIC SYSTEMS

A. General 690-1. Scope. The provisions of this article apply to solar photovoltaic electrical energy systems including the array circuit(s), power conditioning unit(s) and controller(s) for such systems. Solar photovoltaic systems covered by this article may be interactive with other electric power production sources or stand alone, with or without electrical energy storage such as batteries. utilization. These systems may have alternating- or direct-current output for Blocking diodes Module Power B conditioning unit Photovoltaic source A circuits Panel Photovoltaic output circuit Array or Solar Power hotovoltaic cells conditioning power source unit output circuit 1: Disconnecting means required by Section 690-13. : Equipment permitted to be on the photovoltaic power source side of the photovoltaic power source disconnecting means, per Section 690-14, Exception No. 2. See Section 690-16. Diagram 690-1. Solar Photovoltaic System (Simplified Circuit-grounding system not shown) ARTICLE 690 - SOLAR PHOTOVOLTAIC SYSTEMS 70-715 690-2. Definitions. Array: A mechanically integrated assembly of modules or panels with a support structure and foundation, tracking, thermal control, and other components, as required, to form a direct-current power-producing unit. Blocking Diode: A diode used to block reverse flow of current into a photovoltaic source circuit. Interactive System: A solar photovoltaic system that operates in parallel with and may be designed to deliver power to another electric power production source connected to the same load. For the purpose of this definition, an energy storage subsystem of a solar photovoltaic system, such as a battery, is not another electric power production source. Module: The smallest complete, environmentally protected assembly of solar cells, optics, and other components, exclusive of tracking, designed to generate direct-current power under sunlight. Panel: A collection of modules mechanically fastened together, wired, and designed to provide a field-installable unit. Photovoltaic Output Circuit: Circuit conductors between the photovoltaic source circuit(s) and the power conditioning unit or direct-current utilization equipment. See Diagram 690-1. Photovoltaic Power Source: An array or aggregate of arrays that generates direct-current power at system voltage and current. Photovoltaic Source Circuit: Conductors between modules and from modules to the common connection point(s) of the direct-current system. See Diagram 690-1. Power Conditioning Unit: Equipment that is used to change voltage level or waveform, or both, of electrical energy. Commonly, a power conditioning unit is an inverter that changes a direct-current input to an alternating-current output. Power Conditioning Unit Output Circuit: Conductors between the power conditioning unit and the connection to the service equipment or another electric power production source, such as a utility. See Diagram 690-1. Solar Cell: The basic photovoltaic device that generates electricity when exposed to light. Solar Photovoltaic System: The total components and subsystems that, in combination, convert solar energy into electrical energy suitable for connection to a utilization load. Stand-Alone System: A solar photovoltaic system that supplies power independently but that may receive control power from another electric power production source. 70-716 NATIONAL ELECTRICAL CODE 690-3. Other Articles. Wherever the requirements of other articles of this Code and Article 690 differ, the requirements of Article 690 shall apply. Solar photovoltaic systems operating as interconnected power production sources shall be installed in accordance with the provisions of Article 705. 690-4. Installation. (a) Photovoltaic System. A solar photovoltaic system shall be permitted to supply a building or other structure in addition to any service(s) of another electricity supply system(s). (b) Conductors of Different Systems. Photovoltaic source circuits and photovoltaic output circuits shall not be contained in the same raceway, cable tray, cable, outlet box, junction box, or similar fitting as feeders or branch circuits of other systems. Exception: Where the conductors of the different systems are separated by a partition or are connected together. (c) Module Connection Arrangement. The connections to a module or panel shall be so arranged that removal of a module or panel from a photovoltaic source circuit does not interrupt a grounded conductor to another photovoltaic source circuit. (d) Equipment. Inverters or motor generators shall be identified for use in solar photovoltaic systems. 690-5. Ground Fault Detection and Interruption. Roof-mounted photovoltaic arrays located on dwellings shall be provided with ground-fault protection to reduce fire hazard. The ground-fault protection circuit shall be capable of detecting a ground fault, interrupting the fault path, and disabling the array. B. Circuit Requirements 690-7. Maximum Voltage. (a) Voltage Rating. In a photovoltaic power source and its directcurrent circuits, the voltage considered shall be the rated open-circuit voltage. (b) Direct-Current Utilization Circuits. The voltage of direct-current utilization circuits shall conform with Section 210-6. (c) Photovoltaic Source and Output Circuits. Photovoltaic source circuits and photovoltaic output circuits that do not include lampholders, fixtures, or receptacles shall be permitted up to 600 volts. (d) Circuits Over 150 Volts to Ground. In one- and two-family dwellings, live parts in photovoltaic source circuits and photovoltaic output circuits over 150 volts to ground shall not be accessible while energized to other than qualified persons. (FPN): See Section 110-17 for guarding of live parts, and Section 210-6 for voltage to ground and between conductors. ARTICLE 690 - SOLAR PHOTOVOLTAIC SYSTEMS 70-717 690-8. Circuit Sizing and Current. (a) Ampacity and Overcurrent Devices. The ampacity of the conductors and the rating or setting of overcurrent devices in a circuit of a solar photovoltaic system shall not be less than 125 percent of the current computed in accordance with (b) below. The rating or setting of overcurrent devices shall be permitted in accordance with Section 240-3 (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. (b) Computation of Circuit Current. The current for the individual type of circuit shall be computed as follows: (1) Photovoltaic Source Circuits. The sum of parallel module shortcircuit current ratings. (2) Photovoltaic Output Circuit. The photovoltaic power source shortcircuit current rating. (3) Power Conditioning Unit Output Circuit. The power conditioning unit output current rating. Exception: The current rating of a circuit without an overcurrent device shall be the short-circuit current, and it shall not exceed the ampacity of the circuit conductors. (c) Systems with Multiple DC Voltages. For a photovoltaic power source having multiple output circuit voltages and employing a commonreturn conductor, the ampacity of the common-return conductor shall not be less than the sum of the ampere ratings of the overcurrent devices of the individual output circuits. 690-9. Overcurrent Protection. (a) Circuits and Equipment. Photovoltaic source circuit, photovoltaic output circuit, power conditioning unit output circuit, and storage battery circuit conductors and equipment shall be protected in accordance with the requirements of Article 240. Circuits connected to more than one electrical source shall have overcurrent devices so located as to provide overcurrent protection from all sources. (FPN): Possible backfeed of current from any source of supply, including a supply through a power conditioning unit into the photovoltaic output circuit and photovoltaic source circuits, must be considered in determining whether adequate overcurrent protection from all sources is provided for conductors and modules. (b) Power Transformers. Overcurrent protection for a transformer with a source(s) on each side shall be provided in accordance with Section 450-3 by considering first one side of the transformer, then the other side of the transformer, as the primary. Exception: A power transformer with a current rating on the side connected toward the photovoltaic power source not less than the short-circuit output current rating of the power conditioning unit shall be permitted without overcurrent protection from that source. 70-718 NATIONAL ELECTRICAL CODE (c) Photovoltaic Source Circuits. Branch-circuit or supplementary type overcurrent devices shall be permitted to provide overcurrent protection in photovoltaic source circuits. The overcurrent devices shall be accessible, but shall not be required to be readily accessible. C. Disconnecting Means 690-13. All Conductors. Means shall be provided to disconnect all current-carrying conductors of a photovoltaic power source from all other conductors in a building or other structure. Exception: Where a circuit grounding connection is not designed to be automatically interrupted as part of the ground-fault protection system required by Section 690-5, a switch or circuit breaker used as a disconnecting means shall not have a pole in the grounded conductor. (FPN): It is intended that the grounded conductor be permitted to have a bolted or terminal disconnecting means to allow maintenance or troubleshooting by qualified personnel. 690-14. Additional Provisions. The provisions of Article 230, Part F, shall apply to the photovoltaic power source disconnecting means. Exception No. 1: The disconnecting means shall not be required to be suitable as service equipment and shall be rated in accordance with Section 690-17. Exception No. 2: Equipment such as photovoltaic source circuit isolating switches, overcurrent devices, and blocking diodes shall be permitted on the photovoltaic power source side of the photovoltaic power source disconnecting means. 690-15. Disconnection of Photovoltaic Equipment. Means shall be provided to disconnect equipment, such as a power conditioning unit, filter assembly, and the like, from all ungrounded conductors of all sources. If the equipment is energized from more than one source, the disconnecting means shall be grouped and identified. 690-16. Fuses. Disconnecting means shall be provided to disconnect a fuse from all sources of supply if the fuse is energized from both directions and is accessible to other than qualified persons. Such a fuse in a photovoltaic source circuit shall be capable of being disconnected independently of fuses in other photovoltaic source circuits. 690-17. Switch or Circuit Breaker. The disconnecting means for ungrounded conductors shall consist of a manually operable switch(es) or circuit breaker(s) (1) located where readily accessible, (2) externally operable without exposing the operator to contact with live parts, (3) plainly indicating whether in the open or closed position, and (4) having ratings not less than the load to be carried. Where all terminals of the disconnecting means may be energized in the open position, a warning sign shall be mounted on or adjacent to the disconnecting means. The sign shall be ARTICLE 690 - SOLAR PHOTOVOLTAIC SYSTEMS 70-719 clearly legible and shall read substantially: WARNING - ELECTRIC SHOCK - DO NOT TOUCH - TERMINALS ENERGIZED IN OPEN POSITION. Exception: A disconnecting means located on the direct-current side shall be permitted to have an interrupting rating less than the currentcarrying rating where the system is designed so that the direct-current switch cannot be opened under load. 690-18. Disablement of an Array. Means shall be provided to disable an array or portions of an array. (FPN): Photovoltaic modules are energized while exposed to light. Installation, replacement, or servicing of array components while a module(s) is irradiated may expose persons to electric shock. D. Wiring Methods 690-31. Methods Permitted. (a) Wiring Systems. All raceway and cable wiring methods included in this Code and other wiring systems and fittings specifically intended and identified for use on photovoltaic arrays shall be permitted. Where wiring devices with integral enclosures are used, sufficient length of cable shall be provided to facilitate replacement. (b) Single Conductor Cable. Types SE, UF, and USE conductor cable shall be permitted in photovoltaic source circuits where installed in the same manner as a Type UF multiconductor cable in accordance with Article 339. Where exposed to direct rays of the sun, Type UF cable identified as sunlight-resistant or Type USE cable shall be used. 690-32. Component Interconnections. Fittings and connectors that are intended to be concealed at the time of on-site assembly, where listed for such use, shall be permitted for on-site interconnection of modules or other array components. Such fittings and connectors shall be equal to the wiring method employed in insulation, temperature rise and fault-current withstand, and shall be capable of resisting the effects of the environment in which they are used. 690-33. Connectors. The connectors permitted by Section 690-32 shall comply with (a) through (e) below. (a) Configuration. The connectors shall be polarized and shall have a configuration that is noninterchangeable with receptacles in other electrical systems on the premises. (b) Guarding. The connectors shall be constructed and installed so as to guard against inadvertent contact with live parts by persons. (c) Type. The connectors shall be of the latching or locking type. (d) Grounding Member. The grounding member shall be the first to make and the last to break contact with the mating connector. (e) Interruption of Circuit. The connectors shall be capable of interrupting the circuit current without hazard to the operator. 70-720 NATIONAL ELECTRICAL CODE 690-34. Access to Boxes. Junction, pull, and outlet boxes located behind modules or panels shall be installed so that the wiring contained in them can be rendered accessible directly or by displacement of a module(s) or panel(s) secured by removable fasteners and connected by a flexible wiring system. E. Grounding 690-41. System Grounding. For a photovoltaic power source, one conductor of a 2-wire system rated over 50 volts and a neutral conductor of a 3-wire system shall be solidly grounded. Exception: Other methods that accomplish equivalent system protection and that utilize equipment listed and identified for the use shall be permitted. (FPN): See the first Fine Print Note under Section 250-1. 690-42. Point of System Grounding Connection. The direct-current circuit grounding connection shall be made at any single point on the photovoltaic output circuit. (FPN): Locating the grounding connection point as close as practicable to the photovoltaic source will better protect the system from voltage surges due to lightning. 690-43. Size of Equipment Grounding Conductor. The equipment grounding conductor shall be no smaller than the required size of the circuit conductors in systems where the available photovoltaic power source short-circuit current is less than twice the current rating of the overcurrent device. In other systems, the equipment grounding conductor shall be sized in accordance with Section 250-95. 690-44. Common Grounding Electrode. Exposed noncurrent-carrying metal parts of equipment and conductor enclosures of a photovoltaic system shall be grounded to the grounding electrode that is used to ground the direct-current system. Two or more electrodes that are effectively bonded together shall be considered as a single electrode in this sense. F. Marking 690-51. Modules. Modules shall be marked with identification of terminals or leads as to polarity, maximum overcurrent device rating for module protection, and with rated: (1) open-circuit voltage, (2) operating voltage, (3) maximum permissible system voltage, (4) operating current, (5) short-circuit current, and (6) maximum power. 690-52. Photovoltaic Power Source. A marking, specifying the photovoltaic power source rated: (1) operating current, (2) operating voltage, (3) open-circuit voltage, and (4) short-circuit current, shall be provided at an accessible location at the disconnecting means for the photovoltaic power source. (FPN): Reflecting systems used for irradiance enhancement may result in increased levels of output current and power. ARTICLE 690 - SOLAR PHOTOVOLTAIC SYSTEMS 70-721 G. Connection to Other Sources 690-61. Loss of System Voltage. The power output from a power conditioning unit in a solar photovoltaic system that is interactive with another electric system(s) shall be automatically disconnected from all ungrounded conductors in such other electric system(s) upon loss of voltage in that electric system(s) and shall not reconnect to that electric system(s) until its voltage is restored. (FPN): For other interconnected electric power production sources, see Article 705. A normally interactive solar photovoltaic system shall be permitted to operate as a stand-alone system to supply premises wiring. 690-62. Ampacity of Neutral Conductor. If a single-phase, 2-wire power conditioning unit 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 power conditioning unit output rating shall not exceed the ampacity of the neutral conductor. 690-63. Unbalanced Interconnections. (a) Single-Phase. The output of a single-phase power conditioning unit shall not be connected to a 3-phase, 3- or 4-wire electrical service derived directly from a delta-connected transformer. (b) Three-Phase. A 3-phase power conditioning unit shall be automatically disconnected from all ungrounded conductors of the interconnected system when one of the phases opens in either source. Exception for (a) and (b): Where the interconnected system is designed so that significant unbalanced voltages will not result. 690-64. Point of Connection. The output of a power production source shall be connected as specified in (a) or (b) below. (FPN): For the purposes of this section, a power production source is considered to be (1) the output of a power conditioning unit where connected to an alternating-current electric source; and (2) the photovoltaic output circuit where interactive with a direct-current electric source. (a) Supply Side. To the supply side of the service disconnecting means as permitted in Section 230-82, Exception No. 6. (b) Load Side. To the load side of the service disconnecting means of the other source(s), if all of the following conditions are met: (1) Each source interconnection shall be made at a dedicated circuit breaker or fusible disconnecting means. (2) The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed the rating of the busbar or conductor. Exception: For a dwelling unit, the sum of the ampere ratings of the overcurrent devices shall not exceed 120 percent of the rating of the busbar or conductor. 70-722 NATIONAL ELECTRICAL CODE (3) The interconnection point shall be on the line side of all groundfault protection equipment. Exception: Connection shall be permitted to be made to the load side of ground-fault protection, provided that there is ground-fault protection for equipment from all ground-fault current sources. (4) Equipment containing overcurrent devices in circuits supplying power to a busbar or conductor shall be marked to indicate the presence of all sources. Exception: Equipment with power supplied from a single point of connection. (5) Equipment such as circuit breakers, if back-fed, shall be identified for such operation. H. Storage Batteries 690-71. Installation. (a) General. Storage batteries in a solar photovoltaic system shall be installed in accordance with the provisions of Article 480. Exception: As provided in Section 690-73. (b) Dwellings. (1) Storage batteries for dwellings shall have the cells connected so as to operate at less than 50 volts. Exception: Where live parts are not accessible during routine battery maintenance, a battery system voltage in accordance with Section 690-7 shall be permitted. (2) Live parts of battery systems for dwellings shall be guarded to prevent accidental contact by persons or objects, regardless of voltage or battery type. (FPN): Batteries in solar photovoltaic systems are subject to extensive chargedischarge cycles and typically require frequent maintenance, such as checking electrolyte and cleaning connections. 690-72. State of Charge. Equipment shall be provided to control the state of charge of the battery. All adjusting means for control of the state of charge shall be accessible only to qualified persons. Exception: Where the design of the photovoltaic power source is matched to the voltage rating and charge current requirements for the interconnected battery cells. 690-73. Grounding. The interconnected battery cells shall be considered grounded where the photovoltaic power source is installed in accordance with Section 690-41, Exception. 70-723 Chapter 7. Special Conditions