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101 renewable - small wind turbine and article 694 nec 2011

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Last Updated
7th of October, 2018

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The Article 694 in the NEC 2011 deals with NEC regulation for small wind turbines and it is modeled after the PV code’s Article 690.

694.1 Scope: The provisions of this article apply to small wind (turbine) electric systems that consist of one or more wind electric generators with individual generators having a rated power up to and including 100 kW. These systems can include generators, alternators, inverters, and controllers.

Informational Note - Small wind electric systems can be interactive with other electrical power production sources or might be stand-alone systems. These systems can have AC or DC output, with or without electrical energy storage, such as batteries. See Informational Note Figures 694.1 and 694.2.

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Informational Note -Figure 694.1 Identification of Small Wind Electric System Components – Interactive System.

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Informational Note - Figure 694.2 Identification of Small Wind Electric System Components – Stand-Alone System.

Section I (694.1 through 694.7) The scope of the article and definitions for terms specific to small wind systems. The 694 requirements apply anytime they differ from the rest of the code—except for 705 when a small wind system is operated in parallel with primary sources of electricity; The 500 through 516, applies when a system is installed in a hazardous location.

Section II (694.10 to 694.18) it refers to circuit requirements. This section clears how to calculate voltage and current for small wind systems and how to derate conductors. 694.15 refers to overcurrent protection in accordance with 694.12(B).

Section III (694.20 to 694.28) it refers to disconnecting issues. Section 694.20 provides an exception that exempts a wind turbine that uses an output circuit for regulating speed from having a disconnecting means. Section 694.24 allows a shorting switch or shorting plug to be used as an alternative to a disconnect in this case. This makes sense with the understanding that a small wind turbine is a limited current source and that, for some small wind generators, disconnecting the load produces a dangerous situation. This is one of the prime reasons that small wind needed its own article. Section 694.22 (D) allows the installation of rectifiers, controllers, and inverters in nacelles (wind turbine housings) and other exterior areas that are not readily accessible.

Section IV (694.30) covers wiring methods. It requires that flexible cords comply with Article 400 and be identified as hard service cord, listed for outdoor use and water-resistant. DC output circuits in a building must be in metal raceways, from the point of penetration at the building’s surface to the first readily accessible disconnecting means.

Section V (694.40) addresses grounding. It requires that towers and turbine nacelles be attached to an equipment grounding conductor, but exempts attached parts, such as tails, that have no energizing source. Guy wires are not required to be connected to the equipment grounding conductor. Auxiliary electrodes and equipment-grounding conductors are both required for the tower structure. It refers to Article 250, Section III, for most of the details of the grounding requirements.

Section VI (694.50 through 694.56) prescribes signage that is required for various system configurations. It covers grid-interactive systems and stand-alone systems.

Section VII (694.60 to 694.68) prtains to connecting the system to other sources of electricity. This section requires that inverters used in grid-tied systems be listed and identified as utility-interactive and that these systems comply with article 705. Section 694.66 allows inverters on branch circuits to exceed the normal voltage operating range so long as the voltage at the distribution panel remains within the normal limits. The reason that this is important is this: When inverters are pushing power into the grid, they raise the voltage to do so. If there is a long wire run between the inverter and the utility transformer, it is common to raise the voltage higher than the voltage allowed for the utility. Without this option, wind system owners would be required to install larger-gauge wire to limit the voltage rise.

Section VIII (694.70 to 694.75) covers storage batteries, referencing Article 480 for general battery requirements. But 694.70 spells out the current limiting and other battery- specific safety measures that are required, with an emphasis on systems at 48 volts nominal or greater. Section 694.75 also details requirements for charge controllers. One significant requirement is that a single diversion load control cannot be the sole means of regulating battery charging. A utility-connected service does not qualify as a reliable diversion load to meet the second regulating means requirement.

Section IX (694.80 and 694.85) is for systems greater than 600 volts. While there are few, if any, systems in excess of 600 V and, as far as I know, no battery systems over 600 V, serious efforts are made to not have the code limit future developments. So there are avenues left open that are not currently used. Section IX references Article 490 for general requirements and also establishes the basis for determining battery and other circuit voltage for wire and device ratings.

 

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