The “Everything in One Conduit” Solar Installation

Every once in a while, the Tigo service team sends over a photo that tells an entire installation story in a single frame. This one came from an inverter enclosure where the installer routed AC conductors, PV DC conductors, and communication wiring through the same conduit.

At first glance, it may look like efficient wiring- why run multiple conduits when one will do?!

Because the National Electrical Code – and basic signal integrity – say otherwise.

Power conductors and comms wiring don’t mix

Low-voltage communication wiring, like RS-485 or CAT cables, is typically classified as Class 2 or Class 3 circuits.

Disclaimer: This article contains references to the National Electrical Code. If that sounds boring, remember: the Code book is usually opened after something expensive or smoky has already happened.

According to NEC 725.136, these circuits generally cannot share a raceway with power conductors unless the communication cable insulation is rated for the highest voltage present in that raceway. For example, those DC wires are (or should be) rated for 600V. That means the AC conductors AND that CAT5 comm cable must be as well.

And I'll be a bottle of 20-year Michter's that most installers aren't using 600V-rated CAT5/6.

There’s also a practical reason

Even if the Code didn’t exist, physics would still make this a bad idea. Power conductors generate electromagnetic fields. When communication wiring runs alongside them, those fields can introduce electrical noise and signal interference. The result can be intermittent communication faults that are difficult to diagnose. This becomes even more of an issue with powerline communication systems (PLC), and an extreme amount of attention to detail must be maintained throughout the design and installation phases of these applications.

If you’ve ever logged a service call with the phrase:

“The monitoring keeps dropping offline for no reason”

there’s a decent chance wiring separation was ignored somewhere along the line. Like this:

AC and DC conductors sharing the same conduit

While the communication cable is the most obvious issue in the photo, there’s another detail worth discussing: the AC and DC conductors appear to be routed together in the same conduit. After all, they’re both insulated conductors and both eventually land inside the inverter enclosure. The problem is that AC and DC circuits are fundamentally different electrical systems, and combining them in a single raceway introduces a few complications.

From a Code perspective, the relevant guidance is NEC 300.3(C), which requires that conductors in the same raceway be associated with the same circuit or system unless certain conditions are met. In practice, this means installers should avoid mixing unrelated power systems in the same conduit unless the equipment and conductor insulation are rated appropriately and the installation instructions allow it.

Most inverter manufacturers also expect separate raceways for DC PV input circuits and AC output circuits. This simplifies wiring, improves serviceability, and prevents confusion during troubleshooting. There are also practical reasons for keeping them separate:

• Different operating characteristics – DC PV circuits operate continuously at elevated voltage while AC conductors carry alternating current tied to the grid.

• Servicing safety – separating AC and DC circuits makes it much easier for technicians to identify and isolate the correct system during maintenance.

• Cleaner installations – dedicated raceways prevent overcrowding and make conductor routing far easier to inspect.
  

A quick note about the installer

The company responsible for this installation is no longer in business, which unfortunately happens in the solar industry more often than it should. None of this means the installer was intentionally doing something reckless. In many cases, the effort to reduce conduit runs or simplify routing into the equipment enclosure overshadows the rules. Unfortunately, what saves a little time during installation can create confusion or compliance issues later.

And as many service technicians eventually discover, the next person who opens the enclosure inherits every shortcut made during the original installation.

Sort of like racking out sonar equipment on a submarine and immediately knowing exactly who worked on it last.

Q5-E Troubleshooting (WESTPAC 2001)

Rather than speculating on the reasoning behind this decision, the photo serves as a useful reminder that small shortcuts during installation can lead to big service issues later.

Logbook Entry

Solar equipment is getting smarter, more connected, and more complex. That makes clean wiring practices more important than ever.

When it comes to raceways, the rule is simple:

AC, DC, and communications wiring each require their own watch station. A little extra conduit during installation might feel unnecessary at the time. But the next technician who opens the inverter will appreciate it, even if they never know who to thank.