What type of junction box on the roof?

Re: What type of junction box on the roof?

Many types of raintight junction boxes available. Need to be rated at least Nema 3. Make sure it is mounted correct orientation as many can't be laid down. We now use custom gasket sealed plastic boxes hidden under the array. Use lengths of PV wire with MC4 connectors to mate with modules, then run loose end into j-box to transition to THHN. Wire nut splices are OK, but junction blocks or water-resistant splices (Polaris is one brand) are better. Newer NEC codes are requiring the wires be labeled (string 1,2,3,etc) and have labels saying "Photovoltaic Power Source" on all exposed J-boxes and conduit. If your inverter is a grounded type, grounded wire needs to be white, ungrounded wire is black. If not grounded it can't be white - then most use black as the neg. / red as the positive. Red wire (even USE-2) will fade to white if exposed to sunlight though. Lots of guys just tape the ends of a black wire with red tape. Also, its best not to use the electrical convention of black and white wires for the lead down wires. Substitute gray (code allowed for grounded conductors) and something weird like orange for the ungrounded conductors. The next electrician will think twice before hooking up anything to those.