IEEE Std 1361-2014 pdf download – IEEE Guide for Selecting, Charging, Testing, and Evaluating Lead-Acid Batteries Used in Stand-Alone Photovoltaic (PV) Systems.
4.1 Arc hazard Batteries used in low-voltage small stand-alone PV systems can be a source of electric arc hazards. Care should be taken to prevent accidentally shorting the positive and negative terminals, or the positive terminal or negative terminal and any grounded surface of a cell or battery when using non-insulated metallic tools or other metallic objects, such as jewelry. In most cases, battery short-circuit currents can exceed 1000 A. Special electrically insulated tools should be used to enhance safety. In addition, it is prudent to fuse and properly size all conductors in the system to prevent damage to wiring and test equipment in the event of a short circuit or equipment malfunction. Guidance on arc hazards can be found in NFPA 70E [B14]. NFPA 70E cites additional arc hazard references. 4.2 Hydrogen venting Vented lead-acid batteries release hydrogen and oxygen gas as a result of the electrolysis of water. The electrolysis of water is a consequence of the battery charging process and begins to occurs after the battery is fully charged [B10]. As the charge voltage increases, the electrolysis also increases accordingly. To protect against igniting the potentially flammable and/or explosive hydrogen and oxygen mixture inside the vented battery, the National Electrical Code®, Section 480.10 [B13] requires that battery installations use flame-arrester vent caps. Flame-arrester vent caps for vented batteries typically consist of a micro-porous ceramic or plastic foam to prevent a flame or other external ignition source from igniting the hydrogen inside the cell. Valve-regulated lead-acid (VRLA) batteries under normal operation vent only very small quantities of hydrogen, thus room ventilation is generally more than adequate for hydrogen protection as long as charge voltage is controlled. If VRLA battery charge voltage is uncontrolled and reaches excessive levels, then the quantity of hydrogen released can approach that of vented batteries.