Disconnect switches are often overlooked in the planning and installation of commercial PV systems—until they result in cost overruns, code compliance issues, or safety hazards. During a recent roundtable of Pure Power's senior projects managers with decades of solar + storage engineering experience, several key themes emerged around disconnects for string inverters, ranging from National Electrical Code (NEC) changes to O&M implications and system layout strategies.
Disconnects are essential for isolating electrical equipment during maintenance, repair, or emergencies. On both the DC and AC sides of a PV system, disconnects allow technicians to safely service inverters, combiner boxes, and other components without live current posing a hazard.
As Scott Meacham puts it, “Pretend it’s a valve on a hose—if you don’t shut it off before opening the box, you’re going to have water [or electricity] flowing all over where it shouldn’t be.”
But while distinctly a component of safety, disconnects are too commonly forgotten at the initial design stage. When team members select equipment solely based on cost-per-watt, they may not notice that some inverters lack DC or AC disconnects, and may neglect the added cost to include those disconnects later in the project, or be exposed to long-term operational concerns.
The National Electrical Code has evolved significantly in recent years, especially regarding how and where disconnect switches are placed. For example, NEC 2017 specified that disconnects need to be within 10 feet and within line of sight of the inverter. That seemingly small distance constraint had massive implications for site design, especially for centralized string inverter architectures where dozens of inverters would be clustered near a switchboard.
“You can't fit 20 inverters within 10 feet of a switchboard,” says Matt Donovan. “That rule forced us to buy extra equipment and reconfigure layouts.”
Fortunately, NEC 2020 and NEC 2023 revisions brought more flexibility. Disconnect switches can be placed more than 10 feet away, as long as they are lockable and accessible. However, some jurisdictions haven’t adopted the latest NEC editions yet and continue to enforce the older, more restrictive standards. This can lead to costly surprises for project teams unaware of local code adoption.
It’s worthwhile to distinguish between DC and AC disconnects; each serves different purposes, and equipment may include one, both, or neither.
While most string inverters on the market include a built-in DC disconnect, very few come with AC disconnects. That means if the AC disconnect isn't integrated and local code requires proximity, installers must add large, expensive external disconnects.
“We’ve had to install extra boxes the size of the inverter itself just to satisfy that 10-foot rule,” says Scott Meacham.
And in high-voltage systems, like 800V DC designs, finding compatible disconnects becomes even harder. Equipment options are limited, and in some cases, compliance requires invoking Section 691 of the NEC, which provides more leeway for systems over 5 MW.
Even when code compliance is technically met, poor disconnect planning can turn long-term maintenance into a nightmare.
For instance, many carport systems locate inverters or combiners up in the canopy. Without a local disconnect, the technicians have to walk hundreds of feet, sometimes around buildings, to shut down the equipment before they can service it. That adds labor time, costs, and the temptation for unsafe shortcuts.
“Technicians are going to do whatever saves time,” says Travis Lenberg. “If they can spot a fuse holder they can flip, they’ll use it, even if it’s not load-break rated and unsafe. That causes arcing, equipment damage, and is simply dangerous.”
Well-placed disconnects near accessible pieces of equipment, like inverters, combiner boxes, and fuse holders, make life easier for O&M personnel and reduce the chance of unsafe improvisation.
There’s a subtle but significant difference between a disconnect and an isolation device. A disconnect can be opened safely with current flowing through it ("under load"). On the other hand, an isolation device must be opened only after power has been shut down elsewhere.
The NEC recognizes both of them but restricts their use depending on the application. For instance, fuse holders in a combiner box may be utilized as isolation devices but not as disconnects unless there is a sufficient load-break rated disconnect upstream.
The sole use of isolation devices may satisfy the letter of the code, but it often falls short of practical safety. In the real world, people cut corners. As one attendee suggests, “Design your system so even a cowboy installer is protected.”
How you design your system, especially for centralized string inverter designs, impacts disconnect locations and quantities.
Here is a typical architecture: Remote DC combiners are placed throughout a site, with feeders returning to a centralized inverter pad. If the inverters lack built-in DC disconnects, each unit will need its own external disconnect. And if the AC disconnect isn’t integrated either, that’s yet another set of equipment and cost.
In systems over 5 MW, invoking NEC 691 may allow you to eliminate some disconnects completely. But below that threshold, every missing disconnect adds complexity—and dollars.
Where you place disconnects is also a function of the overall site. In a parking lot, for example, equipment is exposed to the public. You don’t want children flipping handles or animals damaging wiring. In such an environment, placing disconnects up in a canopy, fencing them off, or using lockable enclosures adds useful protection.
Utility-scale sites with ground-mount solar have the opposite issue: access may be restricted, but distances are greater. Large site footprints and long cable runs make the case for localized disconnect placement to reduce service complexity.
Choosing a “cheaper” inverter without considering built-in disconnects can lead to increased system cost, longer installations, more complicated and time-intensive maintenance, and safety hazards. That extra 1¢/W saved will disappear all too quickly when you have to add a dozen external AC disconnects or manage complex workarounds for code compliance. Informed decisions early on, involving both engineering and operations teams, will pay off for years to come.
Disconnects are a seemingly small detail of solar system design, but they carry oversized weight in cost, safety, and long-term performance. As codes evolve and equipment options increase, it's more important than ever to align design strategy with real-world O&M practices.
Whether you are designing a commercial rooftop system, a carport canopy, or a utility-scale array, ask yourself:
Where are my disconnects—and are they going to help or hurt me down the line?
The specialists at Pure Power are here to support you and elevate project success to the next level. Contact our team with your questions at info@PurePower.com