The combination of the enclosure, bypass diode, transitioning wiring, connectors, and adhesive makes the jbox a complex component that appears deceptively simple and is not designed to be maintained or serviced. This combination of system behavior and lack of maintainability poses a reliability challenge for the PV module manufacturer, where a service lifetime of 25-years is expected. The importance of design, characterization of the failure and degradation modes, sufficient qualification and durability testing, and manufacturing quality control for the Jbox system (box and connectors) cannot be overestimated since failures of this system account for approximately 18% of 180 fire incidents studied from 1995 to 2012. This study indicates that the jbox with its associated PV connector was the number one cause for a fire, with the second being inverters at 16%. The International Energy Agency’s 2014 report suggests that PV connectors alone may be responsible for up to one-third of PV module fire incidents suggesting that special attention to this component is required.
A junction box is an electrical enclosure that protects electrical conductors at the points where they are spliced, tapped and pulled. These enclosures allow electricians to easily access the conductors to perform work when needed while simultaneously keeping the conductors safe from damage and unauthorized access.
Sometimes, you’ll hear the term “junction box” used to refer to an electrical fixture box. In the true technical definition of a distribution box, wires should connect only to other wires and raceways. However, in practice, the term is also frequently used to refer to many other electrical box types in which wires connect to a fixture such as a ceiling fan, light switch or wall socket.
Sizing a junction box is critical for making sure the junction box functions correctly. In a junction box that’s too small, an electrician may have to bend conductors excessively to fit them fully inside the box, which risks damaging the insulation on the wires. Conductors and other components spaced too closely may also create interference or hazardous conditions.
Article 314 of the National Electrical Code contains most of the key regulations that you’ll need to follow when choosing and installing a junction box. These regulations describe in detail the required junction box size, depending on the number and size of conductors and fittings enclosed within the box.
