How to choose a junction box

In a PV solar system, besides the PV modules, the most expensive parts are batteries and they need

special care for their protection and durability, junction boxes play a key part in it. For selecting a quality junction box, there are different parameters that should be considered, including the following:

• The casing of the junction box: The casing should be heat and UV radiation resistant to protect the system against any undesirable impact of such events. The casing should also be durable against temperature change as it may be used in different environments.
• The junction box should also have a properly designed inner cavity so that in the case of a high current or temperature rising, the inner components are protected from any consequences of sudden temperature rise.
• The junction box should be water and dust resistant adaptable to any environment.

For better safety and protection requirements, some manufacturers have also installed surge protectors in their junction boxes to prevent any damage to the Solar PV modules in case of any sudden surge event. In some products designed for solar array applications composed of many solar modules, there are even intelligent monitoring systems installed inside of the junction boxes. They are designed to be directly connected to the control cabinet or the inverters.

Important specifications of Junction Boxes

There are some common and standard features of a junction box that need to be considered upon their purchase. These features for a sample 2-Rail solar junction designed for BIPV, thin film flexible PV modules are the followings:

• Cable Size: 2.5mm² & 4.0mm² 14/12 AWG
• Rated Voltage: (TUV) 1000V (UL) 600V
• Contact Resistance: ≤ 5mΩ
• Protection: Class ||
• Housing Material: PPO
• Terminal Material: Copper, tin plated
• Protection Degree: IP 65 (IEC 60529)/ IP 67 with Potting (for JBM2 & JBN1)
• Flame Class: UL94V-0
• Temperature Range: -40℃ to +85℃