Solar Combiner Box Basics
In larger solar photovoltaic (PV) systems, multiple solar panels are connected in
series in a string to increase the voltage before going to the inverter. Multiple
strings of the solar panels are also combined together in parallel to produce higher
A solar power combiner box is a device that combines the output of multiple strings of
solar panels for connection to the inverter. This reduces the number of wires that need to go to the inverter.
The solar combiner box houses the input overcurrent protection fuses for several
strings and the combined junction of the inputs into a larger capacity single main output set of wires.
Most Common Types of Solar Combiner Boxes
- Fused Solar Combiner Boxes
- Pre-wired Solar Combiner Boxes
- Non-Fused Solar Combiner Boxes
- Dual Fused Solar Combiner Boxes
- Solar Combiner Boxes with Circuit Breakers
- Multi String Solar Combiner Boxes
Fused Solar Combiner Box
Pre-wired Solar Combiner
Non-Fused Solar Combiner
Dual Fused Solar Combiner
Solar Combiner Box with Circuit Breakers
Multi String Solar Combiner Box
There are several key components that make up a solar combiner box.
Let's start by talking about the enclosure types used for solar combiners. Most solar string
combiners are designed for outdoor use. They most often have NEMA 3R, 4 or 4X ratings,
with NEMA 3R being the minimum requirement for outdoor use. A better choice would be a solar
combiner with a NEMA 4
or NEMA 4X rating. These boxes are available in many different types of material such as non-metallic plastic,
fiberglass and painted steel.In higher humidity areas, or areas with a large
varyence in humidity, you should add a breather vent.
The enclosure is the highest cost single item in the string
combiner design. Mounting your combiner on a north facing wall in the shade will reduce
heat build up within the box.
This is recomended to extend the life of the components inside the unit.
Size can also have an impact. Comparing two
combiner designs with the same internal components, the combiner in the larger
enclosure allows the larger air volume and surface area inside the enclosure to
assist in better cooling of internal components. Smaller also has a beniffet in providing a more conpact
installation but a breather vent should be installed on smaller combiner boxes.
Output wire bend radius is also important in solar combiner box design. Both the NEC (National Electric Code)
and UL (Underwriters laboratory) have requirements for wire bend
radius spacing inside a solar string combiner. There are both opposite wall and adjacent
wall bend radius requirements that are determined by the terminal or lug size
where your output wire is connecting. Bending conductors in the field is time consuming and
can be costly, using a combiner box that provides a straight line to the output connection
without a bend is prefered by most installers.
A solar combiner box (or string combiner) is sinply a electrical component for
combining and housing the solar power cables
coming from your solar panels.
Combiner boxes are usually made of sheet metal, plastic or fiberglass.
If you are going to use one then it will usually be mounted on the roof where the wiring exits
from the solar panels.
Solar panels are usually wired together in a series string of anywhere between
6 to 10 panels. The exact number
of panels wired in the string is usually dependent upon the requirments of your inverter.
The main function of the box is very straight forward. Multiple strings of solar panels are combined in
the box and then a single set of wires (positive, negative and ground) come out of
the combiner box to the inverter.
A Solar Combiner Box will usually have the following components:
The solar combiner box will have either a metal, plastic or fiberglass enclosure
that holds the components and wiring.
The enclosure protects the componets and wires from the sun and moisture.
Most combiner enclosures have a NEMA rating of 3R, 4 or 4X.
Enclosures used for solar ombiner boxes should be UL listed.
Most combiner box enclosures will either include a
latch or side hole for locking the box.
One feature that you should look for in the combiner box is what is called a
(Fuses or Circuit Breakers)
All combiner boxes will have either fuses or circuit breakers. The number depends upon how many strings your box
These protection devices prevent
too much current being sent to the inverter if there is a short in the system.
Fuses are more common than circuit breakers in combiner boxes.
This is because most strings in a solar system can get up to 600 volts and over.
Most DC circuit breakers
are only rated up to 150 volts. Fuse holders used in solar combiner boxes are rated for 600-1000 volts.
A normal setup will have one fuse holder for each
string coming from your system.
Junction blocks used in combiner boxes are electrical connectors used to attach solar cables in the same circuit
without having to cut or splice the solar cables wires. This type of junction blocks
provide an easy way to combine all the solar input strings input into just
one set of output cables requiring higher-current capacity.
Earth Ground Terminals
Electrical power distribution systems are often connected to ground to limit the
voltage that can appear on distribution circuits. A distribution system
insulated from ground may attain a high potential due to transient voltages
caused by arcing, static electricity, or accidental contact with higher
potential circuits. A ground connection of the system dissipates such
potentials and limits the rise in voltage of the grounded system.