PV Module J-Boxes & Mounting Mark Newell and Richard Perez From a user's standpoint, mounting and wiring a photovoltaic (PV) module means dealing with the module's framework and junction box (J-Box). From a dealer/installer's standpoint, they practically live inside J-Boxes. Every make of PV module is different. We decided to photograph, measure, and evaluate the mounting requirements and junction boxes of the most commonly available modules. Here's what we found. Mounting Dimensions and Requirements The table lists the physical dimensions of virtually every available module. Also included on the table are the dimensions between the module's mounting holes and the diameter of the mounting holes. Some modules offer many holes for mounting, some only offer four. Specific module physical differences will be covered under the description of each module. All dimensions given here are from our actual measurements. There are bound to be minor and insignificant variations between the information on this chart and manufacturers' specifications. INSERT DIMENSIONS TABLE J-Boxes After you rack 'em and stack 'em, it's time to wire 'em up. This means getting into the module's junction box and making efficient, long-lasting electrical connections. Each J-Box is different. Some are roomy enough to hold four to eight USE insulated #10 gauge wires, some are not. Some offer massive, high pressure, mechanical connections, others are more wimpy. Some require tools for entry some, do not. Some offer strain- relief for wires, some do not. Some are ready for conduit installation, some are not. INSERT J-Box TABLE Covered in the table are various categories. The category "Positive & negative in one box?" indicates if both the modules positive and negative output are located in the same junction box. In some PV modules, such as the Siemens and ARCO modules, there are two junction boxes on each module, one for positive and one for negative. These boxes are located on opposite ends of the module's backside. The category "J-Box entrance tool" tells what type of tool is required to secure entrance into the module's junction box. The category "Terminal tool" tells what type of tool is required to make the electrical connections within the junction box and "Terminal type" describes the type of terminal found in the J-Box. The category "Connector type" describes the type of electrical connectors, if any, that the connections inside the J-Box are designed to accept. The "Width", "Height", "Depth" and "Volume" refer to the interior dimensions of that J- Box. The category "Roominess" indicates the actual working volume within the box. Consider that a "big" box will allow wiring six to eight #10 gauge wires with USE insulation and "huge", up to ten. A box rated "comfy" will accept four #10 gauge wires with USE insulation. A J-Box rated "Tight" will accept two #10 gauge wires with USE insulation. The category "Conduit Ready?" indicates if the J-Box is designed to accept, and if so how many, either plastic or metal wiring conduits. There are two elements in a long lasting, low resistance, low voltage, mechanical connection. The first element is large contact surface area. The second element is high contact pressure. All the J-Boxes surveyed here have the ability to make a good connection, if the installer does his part. The installer must solder the wires to their connectors. The installer must ensure that the connectors are tightly fastened to the mounting points inside the J-Box. All of the J-Boxes surveyed here, with the exception of the Midway Labs tracker which is metal, are made of plastic. When working with metal screws in plastic, be careful not to over- tighten the screw and strip the threads from the plastic. The place for forceful tightening is the electrical connections within the box, not on the box's lid. While the table gives you much specific information about each module's J-Box, the dimensions alone don't tell the entire tale. Here's a description of each module's particular requirements and a photo of its junction box. ARCO M51 This also ancient module has one of the finest junction boxes we surveyed. It can be accessed without a tool, has palatial volume, and heavy duty electrical connections. Carrizo QuadLam (ARCO M52) The M52 laminates were intended for utility-scale tracked arrays. Each reseller of these recycled laminates now adds his own module mounting framework and junction box to each lam. The ones pictured here are from Carrizo Solar Corp. Carrizo ARCO 16-2000 This ancient module really has no junction box. Two terminals are provided on each end of the module's back. One terminal is positive and one is negative. These terminals are massive, but have no protection from the weather. This type of exposed electrical contact should be coated with silicon rubber to ensure a long lasting, low resistance electrical connection. Kyocera J51 Another fine working J-Box. We like its easy accessibility without using tools, its massive electrical connections, and its roominess. Just for jollies, we have wired eight #10 gauge wires with USE insulation inside this box. Kyocera K51 This is the newer version of the older model "J-series" box. It is smaller than the box on the Kyocera J51 and requires a #2 phillips screwdriver for access. This J-Box is one of three that has it's cover attached. This one has the added feature of screws that permanently a part of the cover. Anybody that has installed PVs on a roof will appreciate this. It also brass posts that the cover screws are screw into. While it was a squeeze, we have wired six #10 gauge wires with USE insulation inside this box. Midway Labs Concentrator This J-Box is absolutely world class. It offers metal construction, serious strain relief, and massive barrier strips. While it is a J-Box, it isn't mounted on the modules, but on the Wattsun tracker holding the 150-sun concentrator PV modules. While it is not fair to compare this box with those on the back of flat plate modules, we included it so you could see what concentrators are using for connections. Siemens M55 This module has two J-Boxes, one for positive and one for negative. While this approach works well for series-wiring modules into high voltage arrays, we have found it more cumbersome for wiring the modules into 12 VDC systems. This J-Box is only one of the two we surveyed that does not require a connector be affixed to the wire. Simply strip the wire's insulation, insert and tighten the large screw. It also has a cover that's attached and won't get lost. Solarex MSX-60 This major power module features a programmable J-Box. The module can be configured to operate at either 6 or 12 Volts. The room in the box is generous and the connectors secure. However, we could do without the little rubber washers and screws to drop and lose in the dirt. Solec S50 This J-Box is very tight, with room for only two #10 gauge wires with USE insulation. The #6 connector size is also smaller than #8 size used in most other modules. The terminal bolts are imbedded in plastic so be careful tightening the nuts. The mounting framework of this module has only four threaded mounting holes. The extrusion used in the framework makes it impossible to drill and use new mounting holes. UniSolar UPM-880 This J-Box has a hinged cover that flips out of the way. It also has the best electrical connections of any surveyed. Instead of post or clamp style electrical connections, the UniSolar uses small brass buss bars. It doesn't use connectors that must be soldered to the wire ends. The stripped wire is inserted into the buss and secured with a screw. This approach has very low electrical loss. Our ideal J-Box looks like this: ù requires no tools for entry ù holds at least eight #10 USE wires ù has only metal to metal screws and holes ù is conduit ready and also has strain relief built in ù is located so that mounting structure does not interfere with opening the J-Box's cover ù has J-Box cover and cover screws (if any) held captive and not drop-able. We are also waiting for the $5 lid and nickel cigar... Access Authors: Mark Newell and Richard Perez, c/o Home Power, POB 520, Ashland, OR 97520 ù 916-475-3179