Photovoltaic module terminal box

Electrical test of a terminal box for photovoltaic modules with a W 434 test device

Testing requirements

A manufacturer produces UV-resistant, water-proof terminal boxes for photovoltaic modules. They include bypass diodes for wires with a wide up to 6 mm2. The diodes avoid that all in-series-connected solar panels are reduced in their performance in case of a partial disconnection. The terminal boxes are specified with a transition resistance of < 2 mOhm and carry operating currents up to 25 A.


For this test a W 434 test device with an adaption table and a programmable generator is being used. First connection test, test of the diodes and short test are performed with low voltage. Than the test system applies up to 25 A from the programmable generator through force wires und measures via sense wires and the integrated voltage meter the voltage drop. The software calculates the resistance according to the Ohm’s law and compares it to the default.

Finally an insulation test with 500 VDC and an electric strength test with 1,000 VAC are performed.

Result / characteristics

The accurate measurement of the voltage drop at high current replaces a time-consuming HOTSPOT measurement. During the HOTSPOT measurement the unit under test is being loaded with 25 A and the temperature is measured at certain transition points. While keeping the same level of accuracy the testing time is reduced from approx. 20 s to approx. 100 ms.