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When Do I Need a Combiner Box?

Jun. 08, 2021

The following is a discussion of the requirements for combining multiple solar arrays using a combiner box from the Combiner Box Manufacturer.

NEC Section 690.9(A) provides the following regulation regarding solar module overcurrent protection: "A PV module or PV source circuit conductor sized in accordance with 690.8(B) does not require an overcurrent device if one of the following conditions exists

Combiner Box

Combiner Box

(a) No external sources, such as parallel source circuits, batteries, or inverter feedbacks.

(b) The short-circuit current from all sources does not exceed the amperage of the conductor or the maximum overcurrent protection device size specified on the PV module nameplate."

This means that if you have more than 1 series of PV modules connected in parallel and the combined short circuit current times 1.56 exceeds the maximum fuse rating on the solar module, then overcurrent protection is required. For example, if you have a 190W Combiner Box with an Isc of 5.8A and a maximum series fuse rating of 10A, and you want to connect the modules in parallel, then each string will need overcurrent protection because the output of 2 modules will be 11.6A, exceeding the maximum rating of 10A. However, if the maximum series fuse rating is 20A, then you can connect 2 modules in parallel because 5.8A X 2 X 1.56 = 18A, which would be less than the maximum rating of 20A.

This means that overcurrent protection is still required; however, the protection can be located on the solar array or the controller. This is a preference and may depend on the site and application. If you have multiple solar array outputs with a single combiner box on the array, having a single output to the controller may be a cleaner solution; however, if you only have 1 or 2 outputs, it may make more sense to combine them on the controller.

We also offer a Module Level Rapid Shutdown, please feel free to contact us if you need one!