Last month, I covered several requirements for small-wind (turbine) electric systems in the new Article 694 of the 2011 National Electrical Code (NEC). My intent for this series is to raise awareness of the new article and discuss its highlights.
Wiring methods—694.30(A) and (B)
This section covers the methods that can be used for the wiring on wind turbines. Basically, the NEC permits all raceway, cable wiring systems and fittings specifically intended for the wiring of turbines.
When turbine-output circuits that operate greater than 30 volts (V) are installed in readily accessible locations, the Code requires them to be installed in raceway systems. Flexible cords and cables of the extra-hard usage identified in Article 400 as service-cord or portable-power cable can be used to connect the moving parts of turbines or for ready removal of components requiring maintenance and repair procedures. Of course, such cords or cables must comply with outdoor conditions of use as outlined in Article 400.
DC output circuits—694.30(C)
Direct current (DC) turbine-output circuits that are installed inside a building or structure must be enclosed in metal raceways or metal enclosures. This requirement applies from the point of penetration of such circuits to the surface of the building or structure to the first readily accessible disconnecting means.
The premise-wiring system must comply with the NEC just as it would for a similar installation connected to a service. If this wiring is connected on the supply side of the building- or structure-disconnecting means, such wiring must be installed in compliance with the NEC. For additional help, see 230.70 through 230.72, and review 230.82. For modification or amendment of the above, see 694.18(A) through (C).
The alternating current (AC) output from stand-alone inverters can supply power to the building- or structure--disconnecting means at current levels less than the calculated load that is connected to the disconnect. However, the -inverter-output rating or the rating of a wind-energy source must not be less than the load of the largest single utilization equipment connected to the system. Do not consider the general lighting loads as a single load.
Sizing and protection—694.18(B)
The conductors between the inverter output and building- or structure--disconnecting means must be sized and based on the output rating of the inverter. The provisions outlined in Article 240 are used to select the protective devices to protect the conductors. Care must be exercised to ensure the devices are located at the output of the inverter.
Single 120V supply—694.18(C)
Where there are no 240V outlets and no multiwire branch circuits involved, the inverter output of a stand-alone small-wind electric system can be used to supply 120V to single-phase, 3-wire, 120/240V service equipment or distribution panels.
The rating of the overcurrent device connected to the output of the inverter must be less than the rating of the neutral bus located in the service equipment. Equipment must be marked with the following words or equivalent:
SINGLE 120V SUPPLY
DO NOT CONNECT
MULTIWIRE BRANCH CIRCUITS
Note that 694.18(D) does not require energy, such as a storage or backup-power supply, to be provided.
Markings—694.50 and 694.52
Section 694.50 covers the marking requirements for an interactive system point of interconnection with other sources. Section 694.52 covers power systems employing energy storage and basically requires that the maximum operating voltage and any equalization voltage, as well as polarity of the grounded-circuit conductor, to be properly identified.
Identification of power sources—694.54(A) and (B)
Section 694.54(A) covers facilities with stand-alone systems. The stand-alone system is not connected to a utility, but it still requires a permanent plaque or directory to be installed on the exterior of the building or structure at a readily accessible location. This plaque or directory must indicate the location of the system-disconnecting means and notify the user that this power source is a stand-alone system.
Section 694.54(B) relates to facilities with utility services and small-wind electric systems. Buildings or structures with both utility and small-wind electric systems must have a plaque or directory indicating where the disconnecting means is located. It is important that the plaque be installed at or adjacent to the turbine location and provides basic instructions for disabling it.
Grounding requirements—694.40(A) through (C)
Equipment-grounding requirements for towers, turbine nacelles, or other equipment are in 694.40(A) and grounding for guy wires is found in 694.40(B). Tower-grounding auxiliary electrode requirements are in 694.40(C)(1), and the equipment-grounding conductor is listed in (C)(2). Tower-grounding connections and lightning-protection techniques are in (C)(3) and (4).
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.