A large solar photovoltaic (PV) cell array may consist of many different solar modules, connected in the form of a series. The combination is required to build voltage up to the requisite levels, for powering the inverter. A solar combiner box combines the output of strings of the PV modules (numbering from 3 to up to 52) and connects it to the inverter. The box may also be used to find out the presence of fault within the strings. A damaged string will result in blowing out of the fuse of the particular string. Hence the use of the combiner box ensures that the inverter is protected from the DC side, and the DC disconnect may be used for the purpose. The box may also have other components like the monitoring hardware and the surge protection devices and is used typically in applications more significant than 500 kW and in the utility and large-scale PV power sources and plants.

Evaluating the Solar Combiner Box

Some of the essential elements and components to be analyzed for evaluating the solar combiner box are given below-


The minimum rating and requirement of a solar combiner box include NEMA (National Electrical Manufacturer Association) rating 4X, 4, and 3R. These can be used and deployed in outdoor settings. However, type 4 and 4X are commonly used, and X denotes the enclosure's capability to resist corrosion. A breather vent or condensation vent may also be added to the box to ensure that the water molecules do not find an entry. The combiner's life may depend on the enclosure, and the rated enclosures are costly as well. The internal temperatures may be affected by factors like color, size, and position, and the lighter colors will absorb less heat compared to the dark colors.

Mounting wall

The combiner box and enclosure should be mounted on a wall that faces north, as such positioning will not increase its temperature significantly during day time. High heat can reduce reliability as well as the life of the internal components of the combiner box. Larger boxes will have more air and hence will provide more significant cooling to the internal components. Large enclosures also provide for convenient wiring, and more space will be available during the maintenance and installation works.

Bending Radius of the Output Wire

Both UL (Underwriters Laboratory) and NEC (National Electric Code) have laid down specific requirements that can be used to evaluate the bending radius of the output wire of a combiner box. These requirements need to be followed for ensuring compliance. The requirements relate to both adjacent and opposite walls, and it is determined by the lug/terminal size where the output wire is connected. Some installers may prefer aluminium conductors over the copper ones because of lesser cost. But the aluminium conductors have the requirement of a larger gauge when compared to copper. Hence a longer bend radius will be required for aluminium conductors, and the combiner enclosure should also be significant. However, when there is an option of a straight forward extension that can reach the output terminal, no bend is required, and installation time is saved. In this case, the mechanical stress on the internal components and wastes is reduced, and lesser time is taken.

Talking to the leading manufacturers of industrial equipment, panels and enclosures can help the industries know more about the specific set of features their industrial procurements like industrial panels, enclosures, and combiner boxes should contain.