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PV Junction Box: purpose and connection

2016-04-26 16:48:09 Prostar Solar Energy Read

A photovoltaic (PV)  junction box is an important part of the solar panels. The junction box is an enclosure on the module where the PV strings are electrically connected.

The majority of junction box manufacturers are nowadays based in China.

Solar panel (PV) junction box


How is the junction box connected to the solar panel?

A PV junction box is attached to the back of the solar panel (TPT) with silicon adhesive. It wires the (usually) 4 connectors together and is the output interface of the solar panel.

Solar PV Junction Box

How to connect the solar panel junction box to the solar array?

With the use of a junction box, it becomes easy to connect the solar panel to array. Usually cables with MC4 / MC5 connectors at the end are used.

Ugly looking silicon around solar junction box

A good junction box keeps corrosion at the terminals to a minimum, as it will exclude water coming in.

When purchasing solar modules, always have a look at the IP rating of the PV junction box. A completely water tight junction box carries IP 67.

MC4 Solar Cables

How does the PV junction box protect the solar panel?

Most photovoltaic junction boxes have diodes. The function of the diodes is to keep the power flow going in one direction, and prevent power from feeding back into the panels when there's no sunshine.

Diodes inside and opened junction box


A quality PV junction box is certified (e.g. via TÜV) and regulates the heat and offers reliable long-term safety.


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