Box Jamboree

Here is a description of each module's particular requirements and a photograph of its junction box. All the photographs (except Midway Labs concentrator) were shot by Mark Newell using the same lens at the same distance from the J-Box. All the resulting photographic prints were reduced by the same amount before printing here. This means that the relatively sizes of the boxes in these photos are a good indication of their relative real physical sizes.

All modules are listed alphabetically by maker.

ARCO 16-2000

This ancient module above 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.


This 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.

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. The photo above shows six #10 USE insulated wires inside.

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 boxes to each Lam. Each Lam has two J-Boxes, one for postive and one for negative. Four Lams are used in series for 12 Volt operation. The J-Box pictured here is from Carrizo Solar Corp's Gold QuadLam.

Kyocera K51

This is the newer version of the "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 its cover attached. This one has the added feature of screws that are permanently a part of the cover. Anybody that has installed PVs on a roof will appreciate this. It also has brass posts that the cover screws are screwed 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.

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.

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.

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.

Our ideal J-Box looks like this:

• requires no tools for entry

• holds at least eight #10 USE insulated wires

• has only metal-to-metal screws and holes

• is conduit ready and also has strain relief built in

• is located so that mounting structure does not interfere with opening the J-Box's cover

• has J-Box cover and cover screws (if any) held captive and not drop-able

We also are very much to be liking this J-Box on the back of a two dollars per watt PV module...


Authors: Mark Newell and Richard Perez, c/o Home Power, POB 520, Ashland, OR 97520 • 916-475-3179

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.

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