Photovoltaic string disconnect switches


Courtesy of Eaton Corporation

PV system arrays generate DC current. The solar modules are wired in series, and the system voltage is the sum of the maximum output voltage of all of the modules in a string. 600 Vdc maximum was chosen as an optimal system voltage to reduce installation costs by reducing conductor size and to stay below the 600V threshold in NEC Article 490.

Prior to the growth in the number of installed PV systems, 600 Vdc was not a common system voltage. Thus, there was a limited availability of protection and switching devices that meet North American standards at this voltage. In addition, the grounding and ground fault requirements of these PV systems varies from that of other DC systems resulting in different switching and bonding schemes.

As the PV industry grows, overcurrent and switch products are intentionally or accidentally being applied in ways that are in conflict with the products’ listings. Added to this, some manufacturers have “self-certified” products for use in ways that are outside of the products’ listing. These situations make it difficult for installers and Authorities Having Jurisdiction (AHJs) to understand how to properly apply or inspect these products. Using or approving a product outside of its listed rating is a violation of NEC Article 210.3, and could open the installer or the AHJ to liability for misapplication of the product.

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