The threat of PV systems starting fires is an unfortunate reality. Since the Bakersfield, CA fire in early 2009, the solar industry has been searching for solutions that not only detect potential fire threats but more importantly stop the problem before it starts. Local jurisdictions have been calling for solutions to these problems and the new 2011 National Electric Code (NEC) includes requirements for arc fault detection and interruption for rooftop PV systems.
According to IDC Energy Insights research analyst Jay Holman, “All too often new fire safety requirements do not make it into the code until a tragic event raises awareness of risks to the national level, but arc-fault protection in rooftop PV systems provides an example of how an industry can take proactive measures to prevent such tragedies from occurring.”
There is a real danger of grounded PV systems creating a condition known as a ‘double ground fault’ in which the positive side of the array essentially shorts to the negative side of the array through the equipment ground conductor. In most cases, the inverter’s GFI is incapable of detecting one of the ground faults or preventing the ground wire from catching fire.
I had the opportunity to stop by the SolarBOS booth at Solar Power International in Dallas last week. There I learned that the manufacturer of electrical Balance of System products offers what they say is the industry’s first working arc fault and ground fault detection and interruption combiner box, as well as a ground fault interruption for PV systems.
The company says the AFDI combiner allows system integrators to meet the letter of 2011 NEC in a cost-effective and reliable manner. The combiner box has a module that detects series arcs and automatically disconnects the ungrounded conductor from the rest of the system, breaking the circuit, which stops the arc and prevents a fire from starting. It can also be configured to work with a Ground Fault Interruption (GFI) device or system to open the ungrounded output of the combiner box when a ground fault is detected.
“Without AFDI or GFI capability at the combiner box, there is no way to automatically shut off the output from a PV array in the case of an arc fault or ground fault in the array wiring,” said Jason Schripsema, CEO of SolarBOS. “The AFDI combiner not only solves this problem and meets the new NEC requirements, it does so in a cost effective way.”