What are Overcurrent Protection Devices ?

Overcurrent Protection Device (OCPD’s) is critical to personal safety and protection from a number of hazardous conditions that can result from materials igniting due to improper overload protection or short-circuit protection. Overcurrent protection devices are meant to protect against the potentially dangerous effects of overcurrents, such as an overload current or a short-circuit current, which creates a fault current.

There are two vital components of OCPD’s:

Maximum Series Fuse Rating is the term mentioned on the back of a PV module (along with rated power, open-circuit voltage, maximum power voltage, short circuit current and maximum power current). This term means that if you had a fuse with a higher current, it would not protect the PV module. In a way, the maximum series fuse rating is like the “ampacity” of the PV module.

The installation of the series fuse for each series string becomes necessary when the series strings are connected in parallel within the combiner box or directly to an inverter that could potentially provide reverse current under fault conditions. These series fuses are often located in a combiner box.

Module interconnects to connect the modules together and can be made with USE-2 and PV wires. 

• Single-conductor Type USE-2 cable and photovoltaic (PV) wire are both ok to use in exposed outdoor installations.Because these installations are usually found in more extreme environmental conditions, the insulation for these conductors must be sunlight resistant and rated for wet conditions and must be able to handle temperatures of up to 90°C.

  
  

• PV wire is solely used for interconnecting PV modules, and was developed to be able to handle 90°C in wet conditions and 150°C in dry conditions.
• USE-2 wire is usually used for connecting terminals of service equipment, and is mostly found underground, and is therefore only rated to handle 90°C in wet or dry conditions.
• Both can be UL rated at 600V.  However, PV wire can also be rated 1000V or 2000V if needed.
• Both wires can be used in grounded PV arrays, but only PV wire can be used in ungrounded ones.