Article 694

Wind Electric Sytems

Part I. General

  1. Scope. This article applies to wind (turbine) electric systems that consist of one or more wind electric generators and their related alternators, generators, inverters, controllers, and associated equipment.Informational Note: Some wind electric systems are interactive with other electric power sources [see Figure 694.1(a)] and some are stand-alone systems [see Figure 694.1(b)]. Some systems have ac output and some have dc output. Some systems contain elec‐ trical energy storage, such as batteries.
  2. Definitions.

Diversion Charge Controller. Equipment that regulates the charging process of a battery or other energy storage device by


Electric power production and

Alternator Rectifier


distribution network

Part VII. Connection to Other Circuits

  1. Transfer Switch. A transfer switch shall be required in non–grid-interactive systems that use utility grid backup. The transfer switch shall maintain isolation between the electrical production and distribution network and the fuel cell system. The transfer switch shall be permitted to be located externally or internally to the fuel cell system unit. Where the utility serv‐ ice conductors of the structure are connected to the transfer switch, the switch shall comply with Article 230, Part V.
  2. Identified Interactive Equipment. Only fuel cell systems listed and marked as interactive shall be permitted in interactive systems.
  3. Output Characteristics. Output characteristics shall beFIGURE 694.1(a) Identification of Wind Electric System Components — Interactive System.
    imageAlternator RectifierChargecontrollerInverterdc loads
    ac loadsin accordance with 705.14.
  4. Loss of Interactive System Power. The fuel cell system

Diversion load


shall be provided with a means of detecting when the electrical production and distribution network has become de-energized

FIGURE 694.1(b) Identification of Wind Electric System Components — Stand-Alone System.

diverting power from energy storage to dc or ac loads, or to an interconnected utility service.

Diversion Load. A load connected to a diversion charge controller or diversion load controller, also known as a dump load.

Diversion Load Controller. Equipment that regulates the output of a wind generator by diverting power from the genera‐ tor to dc or ac loads or to an interconnected utility service.

Inverter Output Circuit. The conductors between an inverter

and an ac panelboard for stand-alone systems, or the conduc‐ tors between an inverter and service equipment or another electric power production source, such as a utility, for an elec‐ trical production and distribution network.

Maximum Output Power. The maximum 1 minute average power output a wind turbine produces in normal steady-state operation (instantaneous power output can be higher).

Maximum Voltage. The maximum voltage the wind turbine produces in operation including open circuit conditions.

Nacelle. An enclosure housing the alternator and other parts of a wind turbine.

Rated Power. The output power of a wind turbine at its rated wind speed.

Informational Note: The method for measuring wind turbine power output is specified in IEC 61400-12-1, Power Performance Measurements of Electricity Producing Wind Turbines.

Tower (as applied to wind electric systems). A pole or other structure that supports a wind turbine.

Wind Turbine. A mechanical device that converts wind energy to electrical energy.

Wind Turbine Output Circuit. The circuit conductors between the internal components of a wind turbine (which might include an alternator, integrated rectifier, controller, and/or inverter) and other equipment.

Informational Note: See also definitions for interconnected

systems in Article 705.

694.7 Installation. Systems covered by this article shall be installed only by qualified persons.

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

  1. Wind Electric Systems. A wind electric system(s) shall be permitted to supply a building or other structure in addition to other sources of supply.imageInformational Note: Testing for certification and listing is typi‐cally performed under the supervision of a qualified electrical testing organization.
  2. Equipment. Wind electric systems shall be listed and labeled or field labeled for the application. Wind electric systems undergoing evaluation for type certification and listing shall be permitted to be operated in a controlled location with access limited to qualified personnel.
  3. Diversion Load Controllers. A wind electric system employing a diversion load controller as the primary means of regulating the speed of a wind turbine rotor shall be equipped with an additional, independent, reliable means to preventover-speed operation. An interconnected utility service shall not be considered to be a reliable diversion load.
  4. Surge Protective Devices (SPD). A surge protective device shall be installed between a wind electric system and any loads served by the premises electrical system. The surge protective device shall be permitted to be a Type 3 SPD on the circuit serving a wind electric system or a Type 2 SPD located anywhere on the load side of the service disconnect. Surge protective devices shall be installed in accordance with Part II of Article 285.
  5. Receptacles. A receptacle shall be permitted to be supplied by a wind electric system branch or feeder circuit for maintenance or data acquisition use. Receptacles shall be protected with an overcurrent device with a rating not to exceed the current rating of the receptacle. All 125-volt, single- phase, 15- and 20-ampere receptacles installed for maintenance of the wind turbine shall have ground-fault circuit-interrupter protection for personnel.
  6. Poles or Towers Supporting Wind Turbines Used as a Raceway. A pole or tower shall be permitted to be used as a raceway if evaluated as part of the listing for the wind turbine or otherwise shall be listed or field labeled for the purpose.
  7. Working Clearances. Working space shall be provided for electrical cabinets and other electrical equipment in accord‐ ance with 110.26(A).

For large wind turbines where service personnel enter the equipment, where conditions of maintenance and supervision ensure that only qualified persons perform the work, working clearances shall be permitted to comply with Table 694.7 for systems up to 1000 V nominal.

Part II. Circuit Requirements

694.10 Maximum Voltage.

  1. Wind Turbine Output Circuits. For wind turbines connec‐ ted to one- and two-family dwellings, turbine output circuits shall be permitted to have a maximum voltage up to 600 volts.
  2. Direct-Current Utilization Circuits. The voltage of dc utilization circuits shall comply with 210.6.
  3. Circuits over 150 Volts to Ground. In one- and two-family dwellings, live parts in circuits over 150 volts to ground shall not be accessible to other than qualified persons while ener‐ gized.

Informational Note: See 110.27 for guarding of live parts and

210.6 for branch circuit voltage limitations.

N Table 694.7 Working Spaces

Nominal Voltage to

0–150900 mm (3 ft)900 mm (3 ft) 900 mm (3 ft)
151–1000900 mm (3 ft)1.0 m (3 ft 6 in.) 1.2 m (4 ft)

Ground Condition 1 Condition 2 Condition 3

694.12 Circuit Sizing and Current.

  1. Calculation of Maximum Circuit Current. The maximum current for a circuit shall be calculated in accordance with 694.12(A)(1) through (A)(3).
    1. Turbine Output Circuit Currents. The maximum current shall be based on the circuit current of the wind turbine oper‐ ating at maximum output power.
    2. Inverter Output Circuit Current. The maximum output current shall be the inverter continuous output current rating.
    3. Stand-Alone Inverter Input Circuit Current. The maxi‐ mum input current shall be the stand-alone continuous inver‐ ter input current rating of the inverter producing rated power at the lowest input voltage.
  2. Ampacity and Overcurrent Device Ratings.
    1. Continuous Current. Wind turbine electric system currents shall be considered to be continuous.
    2. Sizing of Conductors and Overcurrent Devices. Circuit conductors and overcurrent devices shall be sized to carry not less than 125 percent of the maximum current as calculated in 694.12(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 overcur‐ rent devices, listed for continuous operation at 100 percent of its rating shall be permitted to be used at 100 percent of its rating.

694.15 Overcurrent Protection.

  1. Circuits and Equipment. Turbine output 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 694.12(B) where the maximum current from all sources does not exceed the ampacity of the conductors.Informational Note: Possible backfeed of current from any source of supply, including a supply through an inverter to the wind turbine output circuit, is a consideration in determining whether overcurrent protection from all sources is provided. Some wind electric systems rely on the turbine output circuit to regulate turbine speed. Inverters may also operate in reverse for turbine startup or speed control.
  2. Power Transformers. Overcurrent protection for a trans‐ former with sources on each side shall be provided in accord‐ ance with 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 to the inverter output, which is not less than the rated contin‐ uous output current rating of the inverter, shall not be required to have overcurrent protection at the inverter.
  3. Direct-Current Rating. Overcurrent devices, either fuses or circuit breakers, used in any dc portion of a wind electric system shall be listed for use in dc circuits and shall have appro‐ priate voltage, current, and interrupting ratings.

Part III. Disconnecting Means

694.20 All Conductors. Means shall be provided to disconnect all current-carrying conductors of a wind electric power source from all other conductors in a building or other structure. A switch, circuit breaker, or other device, either ac or dc, shall not be installed in a grounded conductor if operation of that switch, circuit breaker, or other device leaves the marked, grounded conductor in an ungrounded and energized state.

Exception: A wind turbine that uses the turbine output circuit for regu‐ lating turbine speed shall not require a turbine output circuit discon‐ necting means.

  1. Additional Provisions. Disconnecting means shall comply with 694.22(A) through (D).
    1. Disconnecting Means. The disconnecting means shall not be required to be suitable for use as service equipment. The disconnecting means for ungrounded conductors shall consist of manually operable switches or circuit breakers complying with all of the following requirements:
      1. They shall be located where readily accessible.
      2. They shall be externally operable without exposing the operator to contact with live parts.
      3. They shall plainly indicate whether in the open or closed position.
      4. They shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment.
      Where all terminals of the disconnecting means are capable of being energized in the open position, a warning sign shall be mounted on or adjacent to the disconnecting means. The sign shall be clearly legible and shall have the following words or equivalent:WARNING. ELECTRIC SHOCK HAZARD.DO NOT TOUCH TERMINALS. TERMINALS ON BOTH THE LINE AND LOAD SIDES MAY BE ENERGIZED IN THE OPEN POSITION.The warning sign(s) or label(s) shall comply with 110.21(B).
    2. Equipment. Equipment such as rectifiers, controllers, output circuit isolating and shorting switches, and over-current devices shall be permitted on the wind turbine side of the disconnecting means.
    3. Requirements for Disconnecting Means.
      1. Location. The wind electric system disconnecting means shall be installed at a readily accessible location either on or adjacent to the turbine tower, on the outside of a building or structure or inside, at the point of entrance of the wind system conductors.Exception: Installations that comply with 694.30(C) shall be permitted to have the disconnecting means located remotely from the point of entry of the wind system conductors.A wind turbine disconnecting means shall not be required to be located at the nacelle or tower.
        The disconnecting means shall not be installed in bath‐ rooms.
      2. Marking. Each turbine system disconnecting means shall be permanently marked to identify it as a wind electric system disconnect. A plaque shall be installed in accordance with 705.10.
      3. Suitable for Use. Turbine system disconnecting means shall be suitable for the prevailing conditions.
      4. Maximum Number of Disconnects. The turbine discon‐ necting means shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchgear.
    4. Equipment That Is Not Readily Accessible. Rectifiers, controllers, and inverters shall be permitted to be mounted in nacelles or other exterior areas that are not readily accessible.
  2. Turbine Shutdown.
    1. Manual Shutdown. Wind turbines shall be required to have a readily accessible manual shutdown button or switch. Operation of the button or switch shall result in a parked turbine state that shall either stop the turbine rotor or allow limited rotor speed combined with a means to de-energize the turbine output circuit.Exception: Turbines with a swept area of less than 50 m2 (538 ft2) shall not be required to have a manual shutdown button or switch.
    2. Shutdown Procedure. The shutdown procedure for a wind turbine shall be defined and permanently posted at the location of a shutdown means and at the location of the turbine controller or disconnect, if the location is different.
  3. Disconnection of Wind Electric System Equipment. Means shall be provided to disconnect equipment, such as inverters, batteries, and charge controllers, from all ungroun‐ ded conductors of all sources. If the equipment is energized from more than one source, the disconnecting means shall be grouped and identified.

A single disconnecting means in accordance with 694.22 shall be permitted for the combined ac output of one or more inverters in an interactive system.

A shorting switch or plug shall be permitted to be used as an alternative to a disconnect in systems that regulate turbine speed using the turbine output circuit.

Exception: Equipment housed in a turbine nacelle shall not be required to have a disconnecting means.

694.26 Fuses. Means shall be provided to disconnect a fuse from all sources of supply where the fuse is energized from both directions and is accessible to other than qualified persons. Switches, pullouts, or similar devices that are rated for the application shall be permitted to serve as a means to disconnect fuses from all sources of supply.

694.28 Installation and Service of a Wind Turbine. Open circuiting, short circuiting, or mechanical brakes shall be used to disable a turbine for installation and service.

Informational Note: Some wind turbines rely on the connection from the alternator to a remote controller for speed regulation. Opening turbine output circuit conductors may cause mechani‐ cal damage to a turbine and create excessive voltages that could damage equipment or expose persons to electric shock.

Part IV. Wiring Methods

694.30 Permitted Methods.

  1. Wiring Systems. All raceway and cable wiring methods included in this Code, and other wiring systems and fittings specifically intended for use on wind turbines, shall be permit‐ ted. In readily accessible locations, turbine output circuits that operate at voltages greater than 30 volts shall be installed in raceways.
  2. Flexible Cords and Cables. Flexible cords and cables, where used to connect the moving parts of turbines or where used for ready removal for maintenance and repair, shall comply with Article 400 and shall be of a type identified as hard service cord or portable power cable, shall be suitable for extra- hard usage, shall be listed for outdoor use, and shall be water resistant. Cables exposed to sunlight shall be sunlight resistant. Flexible, fine-stranded cables shall be terminated only with terminals, lugs, devices, or connectors in accordance with 110.14(A).
  3. Direct-Current Turbine Output Circuits Inside a Building. Direct-current turbine output circuits installed inside a build‐ ing or structure shall be enclosed in metal raceways or installed in metal enclosures, or run in Type MC metal-clad cable that complies with 250.118(10), from the point of penetration of the surface of the building or structure to the first readily accessible disconnecting means.

Part V. Grounding and Bonding

694.40 Equipment Grounding and Bonding.

  1. General. Exposed non–current-carrying metal parts of towers, turbine nacelles, other equipment, and conductor enclosures shall be grounded and bonded to the premises grounding and bonding system. Attached metal parts, such as turbine blades and tails that are not likely to become ener‐ gized, shall not be required to be grounded or bonded.
  2. Tower Grounding and Bonding.
    1. Grounding Electrodes and Grounding Electrode Conduc‐ tors. A wind turbine tower shall be connected to a grounding electrode system. Where installed in close proximity to galvan‐ ized foundation or tower anchor components, galvanized grounding electrodes shall be used.Informational Note: Copper and copper-clad grounding elec‐ trodes, where used in highly conductive soils, can cause electro‐ lytic corrosion of galvanized foundation and tower anchor components.
    2. Bonding Conductor. Equipment grounding conductors or supply-side bonding jumpers, as applicable, shall be required between turbines, towers, and the premises grounding system.
    3. Tower Connections. Equipment grounding, bonding, and grounding electrode conductors, where used, shall be connec‐ ted to metallic towers using listed means. All mechanical elements used to terminate these conductors shall be accessi‐ ble.
    4. Guy Wires. Guy wires used to support turbine towers shall not be required to be connected to an equipment grounding conductor or to comply with the requirements of 250.110.

Informational Note: Guy wires supporting grounded towers are unlikely to become energized under normal conditions, but partial lightning currents could flow through guy wires when exposed to a lightning environment. Grounding of metallic guy wires may be required by lightning standards. For information on lightning protection systems, see NFPA 780-2014, Standard for the Installation of Lightning Protection Systems.

Part VI. Marking

694.50 Interactive System Point of Interconnection. All inter‐ active system points of interconnection with other sources shall be marked at an accessible location at the disconnecting means and with the rated ac output current and the nominal operat‐ ing ac voltage.

694.52 Power Systems Employing Energy Storage. Wind elec‐ tric systems employing energy storage shall be marked with the maximum operating voltage, any equalization voltage, and the polarity of the grounded circuit conductor.

694.54 Identification of Power Sources.

  1. Facilities with Stand-Alone Systems. Any structure or building with a stand-alone system and not connected to a util‐ ity service source shall have a permanent plaque or directory installed on the exterior of the building or structure at a read‐ ily visible location. The plaque or directory shall indicate the location of system disconnecting means and shall indicate that the structure contains a stand-alone electrical power system.
  2. Facilities with Utility Services and Wind Electric Systems. Buildings or structures with both utility service and wind elec‐ tric systems shall have a permanent plaque or directory provid‐ ing the location of the service disconnecting means and the wind electric system disconnecting means.

694.56 Instructions for Disabling Turbine. A plaque shall be installed at or adjacent to the turbine location providing basic instructions for disabling the turbine.

Part VII. Connection to Other Sources

694.60 Identified Interactive Equipment. Only inverters that are listed, labeled, and identified as interactive shall be permit‐ ted in interactive systems.

694.62 Installation. Wind electric systems, where connected to utility electric sources, shall comply with the requirements of Article 705.

694.66 Operating Voltage Range. Wind electric systems connected to dedicated branch or feeder circuits shall be permitted to exceed normal voltage operating ranges on these circuits, provided that the voltage at any distribution equip‐ ment supplying other loads remains within normal ranges.

Informational Note: Wind turbines might use the electric grid to dump energy from short-term wind gusts. Normal operating voltages are defined in ANSI C84.1-2006, Voltage Ratings for Elec‐ tric Power Systems and Equipment (60 Hz).

694.68 Point of Connection. Points of connection to inter‐ connected electric power sources shall comply with 705.12.