You've hit on a common and important point of confusion and potential code violation in PV installations. You're right to question the wireway beneath the inverter. Let's break down why and how it might be compliant or non-compliant with 690.31 of the NEC.

The Problem: NEC 690.31(A) & Exposed Single-Conductor Cables

NEC 690.31(A) generally prohibits exposed single-conductor cables (like PV wire/USE-2) outside of raceways or cable trays. Specifically, it says:"Single-conductor cable Type USE-2 or PV wire shall not be installed exposed to sunlight unless listed and marked as sunlight resistant for use with cable trays."And further sub-paragraphs detail permitted installations within raceways, cable trays, etc. Why this exists

Single-conductor cables are more vulnerable to physical damage and environmental degradation when exposed compared to cables inside raceways. The intent is to protect the insulation and ensure long-term reliability and safety.

Why the Wireway Placement Appears Non-Compliant

In most installations (like the one pictured), the wireway is below the inverter, and the PV conductors often exit the inverter's bottom and enter the wireway without being in a compliant raceway (conduit, cable tray, etc.) from the inverter enclosure all the way into the wireway. This creates a short section of exposed single-conductor cable, violating 690.31(A).

How the Installation Might Be Compliant (or Attempts to Be)

Here's how installations attempt to be compliant, or how they might actually be compliant:1. Raceway Inside the Inverter, Exiting into Raceway

This is the cleanest and safest approach. The inverter manufacturer would need to design the inverter with internal raceways (conduit nipples, integrated conduit bodies) that, when properly connected, provide a continuous, listed pathway from the inverter's internal connections to the external wireway. The conductors would never be exposed between the inverter and the raceway.2.

Shortest Distance Inside Enclosure/Nipple

Some interpretations allow a very short (like 6 inches or less) section of exposed PV wire inside an enclosure or short flexible conduit nipple. The argument here is that because the conductor is contained within a listed enclosure, it's protected. The problem is that NEC section 300.11(C) (for raceways) says raceways must be mechanically secured to the enclosures/junction boxes they enter. An open nipple, such as the photo in the original post, is clearly in violation of this section.
3.

Strategic Entry Point & Partition (Rare)

As you mentioned, this is the trickiest. It involves using a wireway that can be internally partitioned (divided) to physically separate AC and DC conductors. The idea is that the PV conductors enter the wireway directly beneath the inverter output. A partition is then installed to isolate the PV section of the wireway from the rest. This might be considered compliant if the inverter and wireway are listed with an appropriate physical separation, and the AHJ (Authority Having Jurisdiction) approves this interpretation. However, this is generally not considered compliant since the wireway is not a listed, enclosed, and secure raceway that goes all the way back to the inverter enclosure.4.

AHJ Approval (Rare but Possible)

Ultimately, the local AHJ is the final arbiter. They may have specific interpretations or amendments to the NEC. While unlikely, they could approve an installation even if it technically violates the code if they are convinced that the installation provides equivalent safety.

Why Wireways are Still Used

Despite the potential code issues, wireways are often used for a few reasons: Convenience

They make it easier to manage and route the numerous conductors in a PV system.

Cost

Wireways are often cheaper than running individual conduits to each inverter.

Space

Wireways can take up less space than individual conduits, especially in tight installations.

Best Practices for Compliance Plan for Raceways

Design the installation from the start with compliant raceway methods in mind. Specify inverters with appropriate conduit knockouts and plan conduit runs carefully.

Consult the AHJ

Discuss your design with the local electrical inspector before starting the installation. Get their interpretation of 690.31(A) and any other relevant codes.

Choose Listed Components

Use only listed and labeled components, including inverters, wireways, and connectors. Ensure that the components are compatible and rated for the intended use.

Use Proper Terminations

Use appropriate connectors and terminations for PV wire and other conductors. Ensure that the connections are tight and secure.*

Read the Inverter Manual Carefully

The inverter's installation manual should provide detailed instructions on wiring and grounding, including recommended raceway methods.

In Conclusion

The seemingly common practice of placing a wireway directly beneath an inverter without a proper raceway connection is often a violation of NEC 690.31(A). While there are potential interpretations and rare exceptions, the safest and most code-compliant approach is to use proper raceways (conduit) to protect the PV conductors from the inverter to the wireway. Always consult with your local AHJ to ensure your installation meets all applicable codes and regulations. Flag for review