Dear Home Power Readers, Yes, experimenting in photovoltaics is fun--fun for both the amateur and beginner and fun for the experienced electrical engineer. But we must all keep firmly fixed in our minds that when we start implementing real HOME POWER (electricity for our homes), SAFETY is the first and last word. The ability to do work--POWER-- also means the ability to do HARM and electricity can certainly accomplish much destruction and even death if used improperly and/or unwisely. A single twelve volt PV module cannot do much harm, but several modules connected to even a modest battery pose a significant hazard. The regional and national building codes and the National Electrical Codes were developed for our safety. As more and more areas of the country become civilized, greater areas will come under code jurisdiction. Although the codes and sometimes the inspectors are a little slow to respond to the latest technology, they in general do provide safe guidelines for building and wiring our homes. Many of us who are shade tree mechanics and back yard do it yourselfers feel that moving up to a PV powered home is second nature - as easy as falling off a log and not much more difficult than an afternoon tune up on an old truck. Although some of the principles are the same, the IMPLEMENTATION IS FAR DIFFERENT. PV systems can and have caused serious fires. Insurance companies may not insure a PV powered house unless wired by a competent person. Death can result from improper design, under rated components and improper installation. Wire may burn, batteries may explode, inverters may catch on fire, and other equally nasty events can ruin you and your families day unless your PV system is safely installed. THE BOTTOM LINE-- None of us can afford to experience property damage, injury, or loss, of life from a PV related accident. The PV industry cannot afford a string of such accidents. If such accidents started to become common place as our industry grows, then both the insurance companies and the building inspectors would shut us down. BE SAFE--GET HELP FROM A QUALIFIED PERSON IF YOU ARE UNSURE ABOUT WHAT YOU ARE DOING. Sincerely, John Wiles Wiring for Reliability and Performance John Wiles PV Modules will last more than 25 years and the rest of the system should be designed and assembled to provide equal reliability. Good Interconnections - A Must Good module interconnections are a must. Stranded 10 gauge USE wire is a good start. On older modules which have terminal screws and junction blocks, it is suggested that crimped and soldered ring terminals be used. Uninsulated terminals crimped with a crimping tool specifically designed for that style are best. Although solder has a higher resistivity than copper, it fills all of the remaining air voids and provides numerous parallel current paths to improve the connection. Insulated terminals can be used as a second choice, and they should also be soldered. If the screws are captive, then use spade terminals with hooked ends. With newer modules, be sure to torque the terminal screw and clamp to the manufacturer's specification. Hardware, auto supply stores and electrical supply houses usually carry ring and spade terminals. A mail order source is: Marlin P. Jones & Assoc., Lake Park, FL 407-848-8236. Wire Since stranded USE wire is not cheap, it is frequently spliced to a more reasonably priced wire or cable a short distance from the modules. Enough stranded wire should be used to allow for tracker motion and module servicing. Number 10-2 with ground type UF cable is a good low-cost choice to run from the area of the modules to the PV disconnect switch. A black or dark grey outer jacket is preferred for maximum sunlight resistance. On larger arrays, the wire gauge must be increased to handle the higher current and keep the losses to a minimum. Grey PVC conduit could also be used. Splicing The wires in this cable should be firmly twisted, soldered and then taped to the module interconnect wiring. Pressure connectors could be used for convenience in servicing, but the possibility of losses increases. The splices must be installed in an improved rainproof box which can be obtained at electrical supply houses for less than $20.00. Ask for a NEMA 3R box in the size needed. This junction box should be equipped with the proper bushings and cable clamps to prevent physical abuse to the wires and cables as they enter the knockouts on the box. More next issue from John Wiles at the SWRES.