The combiner box of today does more than just hold wires and fuses.
Most solar product names are self-explanatory — an inverter inverts, a tracking system tracks, an optimizer optimizes. And even though a combiner box falls in this self-explained category (because, after all, its main job is to combine circuits), its role has become more complicated, but for all the right reasons. This box now has the capability to offer ways to disconnect, monitor and safely shut down a system completely.
“It starts very simple, but there are a lot of things you can pile into that combiner box once you have it,” says Daniel Sherwood, director of electrical products for SunLink. “First it was just some fuses and a convenient place to land all your conductors. As time went on, once you have a box on the roof it’s just a convenient place to put other functionality.”
Updates to the National Electrical Code (NEC) for 2014 will eventually require new protections, and a logical place to house them will be in the combiner box. While enforcement of these new requirements won’t happen any time soon, it doesn’t hurt to explore combiner box options now when starting a new project.
SunLink, probably more recognized as a mounting system manufacturer, has been involved in the combiner box market since 2010 when it acquired the Blue Oak PV Products combiner box line and rebranded it under the SunLink name. SunLink’s new sales goal is to provide one-stop shopping for solar customers.
“If you buy a SunLink combiner box, we thought about how to mount it with our equipment easily,” Sherwood says. “If you want to get wire harnesses, we can sell that to you, as well as wire management products like clips and trays that fit nicely under our mounting systems. Basically you buy your inverter, you buy your modules [and] the rest of the stuff you can get from SunLink, in terms of the DC equipment — the mounting, the wiring, the clips, the cables trays.”
SunLink produces the average-size HomeRun line of combiner boxes and the smaller HomeRun LTE line. The smaller line is for smaller installations that don’t have a large amount of thick wires looking for a home. Sherwood says the LTE line is the smallest out of all competitors, and it’s also the cheapest.
“We thought of an innovative way to make it work in a smaller box, the way we place the guts of the box a little differently than other people do,” he says. “By allowing it to be smaller, it’s a cost savings. About a third of the cost of a combiner box is just the actual box. Having a smaller one, you save money.”
A smaller box also ships more easily and cheaply because more can fit on a truck. The LTE line is lighter and more easily mountable.
“We found a lot of boxes on the market now are nice if you want a lot of room for big wires, but it makes the box very bulky and it’s hard to mount and it’s heavy,” Sherwood says. “We wanted to give people both options.”
The LTE line features fuses mounted to the sidewall of the box instead of the backplate, a patent-pending design.
“When the fuses are on the backplate, you have to leave room to fit your hands in to get the wires in,” Sherwood says. “When it’s on the side, you make use of the vertical space above the fuses, [and] you can actually fit them in a smaller area. As an added bonus, because the terminals of the fuses are now pointing straight up out of the box, you can see them and it’s easier to work on them.”
Many useful extras have gradually been added to the insides of a combiner box besides the basic combining of circuits and fuses.
“The primary function [of a combiner box] is overcurrent protection and a convenient place to put a disconnect,” Sherwood says. “By code, you need a means of disconnecting your circuit. Most combiner boxes now will include a manual disconnect.”
Monitoring is often included in combiner boxes as well.
“If a tree branch falls on one of the strings, you’re probably not going to notice that it’s not producing power at the inverter level,” Sherwood says. “But if you put monitoring in the combiner box, you can see that the one string is gone right away. You can address the issue.”
The NEC often dictates what additions will be made to combiner boxes in the future. The general public typically runs a cycle behind each new NEC update. For example, the 2011 code will be adopted in California in 2014. This is to make sure everyone understands the code before it’s enforced. Arc fault protection was a requirement in 2011, and Sherwood says he’s just now starting to see people request it.
“If your inverter doesn’t provide [arc fault protection], the combiner box is convenient to put it into your circuit,” he says. “In the 2014 code, there’s now a requirement to have a shut-off capability. No one has adopted it yet, but the combiner box will be a very convenient place to put that as well.”
Any conductors more than 10 ft from the solar array will need to be disconnected in case of a fire, according to the 2014 code, so when firefighters arrive on site, they know their axes won’t hit any live wires. A button could be located somewhere for firefighters to remotely activate a disconnect in the combiner box.
Even though the new shut-off requirement has been introduced, don’t expect next year’s combiner boxes to be ready to meet that need. It’s simply something to be aware of at this point, Sherwood says. When buying a combiner box for a new project, he suggests covering the basics — make sure it fits your needs, it’s properly rated for your application (weatherproof, corrosion-resistant, etc.) and it’s sturdy.
“Look for a quality construction box,” Sherwood says. “If things come loose or they fail, it’d be pretty catastrophic.”
The combiner box is a simple design, but as additional safety requirements come down the pipe, it gets more high-tech and complicated. Knowing your project’s requirements will help find the right combiner box and any extra add-ons perfect for your situation.