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Electrical And Enclosure Safety For Solar Energy Projects

Mon, 05/02/2011 - 11:51am
Jeff Seagle, President, Stahlin Non-Metallic Enclosures

Electrical fires consistently rank among the top five causes of commercial building fires, according to the National Fire Protection Association (NFPA). Fires involving electricity also regularly result in a higher percentage of property damage than those caused by many other sources. One of the most effective ways to better protect property against electrical fires is through education.

Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors. As more plants move towards alternative sources of energy, building maintenance personnel face new demands when it comes to safety and compliance. Notably: When dealing with solar energy projects, your typical electrical safety program may need to be revised to address more complex requirements.

Arc-Faults and UL 94 Arc-Faults

Arc-faults pose the greatest fire risk to PV installations. Detecting and extinguishing arc-faults in DC PV systems will require the development of new devices called DC PV Arc-Fault Circuit Interrupters (DC PV AFCIs), designed to detect and stop the signature of an arc-fault.

The 2011 U.S. National Electric Code (NEC) includes a requirement for arc-fault protection in certain new rooftop PV systems. In response, solar industry vendors are already developing technologies that not only meet this requirement, but surpass it, and provide additional protection against PV system fires. Make sure your vendors are aware of the latest safety codes.

Testing

There are two types of pre-selection test programs to measure flammability characteristics. The first determines the material’s tendency either to extinguish or to spread the flame once the specimen has been ignited. The first program is described in UL 94.

The second test program measures the resistance of the plastic to electrical ignition sources. The material’s resistance to ignition and surface tracking characteristics is described in UL 746A, which is similar to the test procedures described in IEC 60112, 60695, and 60950.

The UL 94 flame ratings group materials into categories based on their flammability: horizontal and vertical burn.

Horizontal Testing: A specimen is supported in a horizontal position and is tilted at 45 degrees. A flame is applied to the end of the specimen for 30 seconds or until the flame reaches the 1 inch mark. If the specimen continues to burn, the time for the specimen to burn between the 1 and 4 inch marks are recorded. If the specimen stops burning before the flame spreads to the 4 inch mark, the time of combustion and damaged length between the marks is recorded.

Vertical Testing: Testing is done on both bar and plaque specimens. A bar specimen is supported in a vertical position and a flame is applied to one of the lower corners of the specimen at a 20 degrees angle. The flame is applied for 5 seconds and is removed for 5 seconds. The flame application and removal is repeated five times.

The procedure for plaques is the same as for bars except, that the plaque specimen is mounted horizontally and a flame is applied to the center of the surface.

Update of Codes & Standards

Oregon is in the process of drafting a solar energy code that would establish fire-safety measures such as setbacks and placement requirements for rooftop panels. The code also creates standards for panel assembly and installation, requires inspections of the systems, and gives firefighters official authority to disconnect the systems.

Other standards are in development, many in areas we might be used to working with. Fire codes are being developed that will determine the roof array size, the size of walkways between the modules, and the access clearance around the roof perimeter and interior walls. Disconnect switches, equipment labeling, cable placement, grounding requirements, and lightning protection standards are also being developed.

Understanding the codes and educating others is essential when working on PV projects. Any negative press focused on fire-safety in our industry can hold growth to a standstill, so choose vendors that are up-to-date as well. We can all stay safe and help our industry remain competitive.

For more information on Stahlin Non-Metallic Enclosures visit: www.stahlin.com.

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