Electrical and Enclosure Safety for Solar Energy Projects

Efficiency is an issue as well. But more than everything, safety is. In this article, you will understand the hazards you might encounter while operating or maintaining PV electrical installations.

By Jeff Seagle

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 address life safety concerns and better protect property against electrical fires is through education.

Electrical Codes: Background

Electrical codes arose in the 1880s with the commercial introduction of electrical power. The first electrical codes in the United States originated in New York in 1881 to regulate installations of electric lighting. Since 1897, the U.S. National Fire Protection Association, a private nonprofit association formed by insurance companies, has published the National Electrical Code (NEC).

States, counties or cities often include the NEC in their local building codes by reference along with local differences. The NEC is modified every three years. It is a consensus code considering suggestions from interested parties. The proposals are studied by committees of engineers, tradesmen, manufacturer representatives, fire fighters, and other invitees.

Electrical safety in the workplace is governed by a number of federal and state requirements that stem from the Occupational Safety and Health Act of 1970 (OSHA) and the National Electrical Code, which was developed by the NFPA.

Electrical Safety: Writing Safety Programs

The first step a business should take is to establish a written electrical safety program. Training and guidelines are a must for anyone working on or around electrically energized systems and equipment. If possible, work areas should be set up away from possible electrical grounds that may come into accidental contact with electricity.

Electrical Employee Safety Program: Some Items to Include

-How to identify electrical hazards.

-What is considered a safe distance from exposed electrical conductors.

-Information about personal protective equipment for electrical safety.

-How to understand proper work practices in wet or damp locations containing electricity.

-The proper lockout/tag-out procedures for electrical equipment and systems.

-Note to unplug tools and equipment before cleaning, adjusting, or repairing them.

-Lock the power switch in the ‘off’ position and pull fuses to prevent a person or a time clock from starting equipment under repair.

-Replace guards over augers, chains and belts before unlocking or refusing the power switch.

-Always follow the lockout, tag-out and grounding procedures appropriate for the work environment.

-Use the recommended wattage when replacing light bulbs or the recommended amperage when replacing fuses.

-If circuit boards need to be removed from their mountings, put insulating material between the boards and anything to which they may short. Hold them in place with string or electrical tape. Prop them up with insulation sticks?plastic or wood.

Special Considerations for Solar Energy Project: 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 the signature of an arc-fault in the current of a PV system and stop the current from flowing through the 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 codes /safety rules and you include them in your employee safety program.

UL 94, the Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances Testing

There are two types of pre-selection test programs conducted on plastic materials 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 which is now harmonized with IEC 60707, 60695-11-10 and 60695-11-20 and ISO 9772 and 9773.

The second test program measures the ignition 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.

UL flame ratings group materials into categories based on their flammability. UL 94 covers two types of testing: vertical burn and horizontal burn.

Horizontal Testing

Procedure: A specimen is supported in a horizontal position and is tilted at 45°. 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 after the removal of the flame, 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 two marks is recorded. Three specimens are tested for each thickness.

Vertical Testing

Testing is done on both bar and plaque specimens.

Procedure for Bars: 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° angle. The flame is applied for 5 seconds and is removed for 5 seconds. The flame application and removal is repeated five times.

Procedure for Plaques: 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 lower surface of the plaque.

Difference in Test Methods and Criteria

When looking at the flame ratings for plastic materials commonly molded to fabricate enclosures, structural parts and insulators found in consumer electronic products (5VA, 5VB, V-0, V-1, V-2 and HB), a material classified as 5VA or 5VB is subjected to a flame ignition source that is approximately five times more severe than that used in the V-0, V-1, V-2 and HB tests.

Stahlin has passed and UL File number: E333478 denotes Stahlin enclosures as a photovoltaic combiner box component and recognizes the required achievements obtained under prior UL 746C, Polymeric Materials ‘Use in Electrical Equipment Evaluations’ for outstanding UL94-5V flammability rating. UL94-5V is a standard that not all current enclosure products have attained, especially in tandem with NEMA 6 or 6P type ratings established under UL-50, Enclosures for Electrical Equipment.

Keeping Up to Date Is Essential: Some Important News Updates

Staying up to date on new codes and rules is essential as everything is constantly changing and evolving. Below are just a couple of important new developments happening in the solar industry:

UL Awarded Grant to Study Firefighter and Photovoltaic System Safety

This grant funds a project that addresses first responder concerns about fighting fires involving Photovoltaic (PV) modules. This research project will investigate firefighter vulnerability to electrical and casualty hazards when fighting a fire involving PV modules and support systems in residential and commercial buildings.

The increasing use of PV systems necessitates this project. PV use is growing at a rate of 30% annually in the U.S. The use of this new technology has complicated traditional firefighter tactics, leaving firefighters vulnerable to severe hazards. Although the electrical and fire hazards of PV systems are addressed through current product standards and certification, a limited body of knowledge and insufficient data exists for the fire services to develop safe tactics during suppression and ventilation activities.

Evaluating the hazards associated with PV systems in firefighting operations will require the design of experimental methodologies based on UL’s historical and current expertise in product testing and standards development. The experiments will develop empirical data to understand the magnitude of the hazards. Methodologies will be based on electrical principals, fire dynamics and firefighting tactics.

UL will share the results and information gained through the research with the fire service community and PV industry through Web-based educational programs, presentations and articles. The results from the study will serve as the foundation for potential PV installation code revisions and the creation of tactical and operational guidelines resulting in improved firefighter preparedness and safety.

To better understand the results login at:

http://www.greenbuildingfiresafety.org/green_fire_initiatives/solar.html

Update of Codes and 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 as well as cut-off switches for the wires leading from the panels to inverter boxes. The code also creates standards for panel assembly and installation, requires inspections of the systems, and gives firefighters official authority to disconnect the systems during emergencies.

Other standards are in development, many in areas we might be used to working with. Fire codes (both local and national) are starting to be developed that will determine the roof array size, the size and number of walkways between the modules, the access clearance around the roof perimeter and interior walls, and the amount of array clearance around skylights and other rooftop equipment so that firefighters can vent a fire if needed. Disconnect switches, cable and array equipment labeling, cable placement, grounding requirements, and lightning protection standards are being developed. Other agencies are starting to work on permits and system approvals. With a typical PV power string having up to 600 volts DC, safety is very important.

Codes and Standards for PV: Article 690 of the National Electric Code

The primary safety and wiring code for PV is covered by Article 690 of the National Electric Code (NEC), which addresses safety requirements for the installation of PV systems. The latest version is NEC 2008. However, many local building codes may still be using NEC 2002 or 2005. Best practice would be to use the NEC 2008. The NEC covers everything from module installation, wiring, and grounding to connector boxes and inverters.

The best source to learn more about PV and the NEC can be found at:

www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/PVnecSugPract.html.6

Performance and Safety Standards for Individual Solar Components in the United States Are Set by Underwriters Laboratories Inc. (UL)

The benchmark UL standards are:

-UL 1703 for PV modules;

-UL 1741 for solar inverters.

All components should carry a UL label. In most cases, one cannot receive incentives and rebates for array systems that have not been UL-certified. (Certification can come from other test facilities but will still use the UL benchmark standards.)

Stahlin Non Metallic Enclosures Understands the Importance of PV Safety 

We were aware of the importance of safety to PV installations, which is why we set a goal of getting our product certified from UL. In 2010, Stahlin Non-Metallic Enclosures achieved UL-recognized component status as certified within the category of Distributed Generation Power Systems Accessory Equipment.

Stahlin enclosures were evaluated under the UL1741 standard for inverter, converter, controllers and interconnection systems equipment for ‘Use With Distributed Energy Resources’ within the United States. Stahlin enclosures were also evaluated under the CSA-C22.2 No. 107.1 ‘Standard for General Use Power Supplies’, for use in Canada.

UL File number: E333478 denotes Stahlin enclosures as a photovoltaic combiner box component and recognizes the required achievements obtained under prior UL 746C, Polymeric Materials ‘Use in Electrical Equipment Evaluations’ for outstanding UL94-5V flammability rating.

UL94-5V is a standard that not all current enclosure products have attained, especially in tandem with NEMA 6 or 6P type ratings established under UL-50, Enclosures for Electrical Equipment.

For more information on this code visit:

http://ulstandardsinfonet.ul.com/tocs/tocs.asp?fn=1741.toc

Educate Yourselves and Your Staff

Understanding the codes and educating others is essential when working on PV projects; especially as we attempt to grow our industry. Any negative press focused on fire-safety in our industry can hold growth and potential to a stand still. Stay up to date on codes and choose vendors that are up to date as well. We can all stay safe and help our industry remain competitive.

Jeffrey Seagle, President of Stahlin Non-Metallic Enclosures (www.stahlin.com), has more than 20 years of experience in the electrical enclosures industry. As President, he has led the company to significant growth through innovative product initiatives, such as the patented composite formulation, SolarGuard®, and helped Stahlin move into a leadership position in their market. Under his leadership, Stahlin was selected as one of the ‘101 Best and Brightest Places‘ in Michigan. Seagle earned his BSME from Purdue University and his MBA from Carnegie Mellon University.

REFERENCES

http://www.greenbuildingfiresafety.org/green_fire_initiatives/solar.html

http://www.buildinggreen.com/auth/article.cfm/2010/9/14/Making-Green-Buildings-Safe-for-Firefighters/

http://www.solar-pv-management.com/solar_news_full.php?thumb_id=153&newsid=73454&title=PV%20fire%20prevention

http://www.ides.com/property_descriptions/UL94.asp

http://www.ul.com/global/eng/pages/offerings/industries/chemicals/plastics/testing/flame/

http://www.mrca.org/i4a/pages/index.cfm?pageID=4765

http://en.wikipedia.org/wiki/Electrical_wiring

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