Wiring It's easy to overlook the wiring and interconnection components required for PV systems. But there is probably no field-installed equipment that is more important for long term system operation. All wiring and electrical components should follow the guidelines of the National Electrical Code, and should be properly approved by the manufacturer and appropriate rating agency (usually UL). Solar Power Wires - Module interconnect wires must be sized for the expected current, as well as attached securely to junction boxes and racks. Loosening connections as a result of constant rooftop heat cycling is a common reason for poor solar power system performance. Ground Wires - All exposed equipment, including solar electric modules, inverters and switch boxes, shoujld be properly grounded. Lightening protection should be provided depending on local code requirements. Roof Penetration - Every time you poke a hole in a roof for rack mounts or wiring you create the potential for leaks. Flashing should surround large roof penetrations, and urethane caulking should be used for smaller penetrations and rack mounts.     Rooftop Conduit - Your home or commercial roof is a very hostile environment. Except for short cable runs we usually use metal conduit to protect wiring from high temperatures and UV radiation. Connections are always made in a junction box according to the National Electric Code. Paralleled Inverters - Multiple inverters can be combined to provide additional solar energy output. This picture shows a 1500 watt and 2500 watt inverter wired together for a 4000 system. Solar Power Output Meter- For performance monitoring purposes it is extremely useful to have an independent, non-volatile record of the gross output provided by the solar electric system. The separate solar electric meter shown in this picture logs the output of these two inverters. AC Disconnect - Many utilities require a separate AC disconnect to isolate the solar power system from utility power. Most solar power systems also include a DC disconnect to isolate the array output from the inverter. This is used in the event of a power outage from your local utility. Your solar array is still producing power and could feed power into the grid via the electrical lines while the utility repairperson is trying to solve the outage problem.