Last Updated: April 10, 2026
NEC 2026 Article 690.31(B)(2) requires permanent polarity marking on all ungrounded DC conductors at every termination, connection, and splice point. Positive conductors must display "+", POSITIVE, or POS. Negative conductors must show "−", NEGATIVE, or NEG — on insulation that is not green, white, gray, or red. Failing to label correctly is a common reason solar inspections get red-tagged.
Your inspector just red-tagged the job. The wire runs are clean, the rapid shutdown system is in, and the permit set matches the install — but the DC conductor polarity labels are wrong. It happens on more jobsites than most installers expect.
Under NEC 2026 Article 690.31(B)(2), positive and negative DC conductors in PV systems must be permanently marked with specific approved text on specific insulation colors. Get either one wrong and the install fails. This guide covers exactly what the code requires, where labels go, what changed from NEC 2023, and how to choose the right marking method for field conditions.
What Does NEC 2026 Article 690.31(B)(2) Actually Require?
NEC 2026 Article 690.31(B)(2) requires all ungrounded DC conductors in a solar PV system to be identified for polarity at every termination, connection, and splice point. The code permits color coding, marking tape, tagging, or other approved means — but when you're not relying on conductor color alone, you must use a permanent marking method.
For permanent markings, the code is explicit:
- Positive conductors must carry an imprinted plus sign (+), the word POSITIVE, or the abbreviation POS — durably marked on insulation that is not green, white, or gray.
- Negative conductors must carry a minus sign (−), the word NEGATIVE, or the abbreviation NEG — on insulation that is not green, white, gray, or red.
Why does red get excluded from negative conductors? Red is associated with a specific ungrounded polarity convention in other NEC DC systems sections, so the code bars it from negative conductor identification to eliminate polarity confusion across the installation.
Key Takeaway: "Close enough" doesn't pass inspection. A label reading "NEG" on red insulation still fails — the insulation color restriction applies regardless of what the label says.
What Colors Can You Use for DC Conductor Polarity Marking?
The NEC does not mandate specific insulation colors for PV DC conductors. It tells you which colors you cannot use. That flexibility is useful in the field, but the restrictions are firm.
Colors you cannot use:
| Conductor | Forbidden Insulation Colors |
|---|---|
| Positive DC | Green, White, Gray |
| Negative DC | Green, White, Gray, Red |
Common compliant choices in the field:
- Positive: Black, Brown, Orange, or Red (positive only — Red is prohibited for negative)
- Negative: Black, Blue, Yellow, or White covered with compliant marking tape at all connection points
AHJ Variation: Authorities Having Jurisdiction vary on how strictly they enforce color vs. permanent marking. Phoenix-area AHJs routinely reject installs where polarity identification relies on wire color alone without permanent labels at terminations. Always confirm requirements with your specific AHJ before permit submittal.
For field-run conductors, Print Pro AZ recommends durable solar DC polarity labels rated for outdoor UV exposure — not generic tape that fades or peels within a season.
Where Do DC Conductor Polarity Labels Go on a PV System?
Article 690.31 requires polarity identification at all termination, connection, and splice points. That means every one of the following locations:
- Every combiner box connection
- Every junction box or enclosure
- Every splice inside a conduit body or pull box
- Inverter DC input terminals
- Array disconnect — both line and load sides
For conductors run in conduit, NEC 690.31(G)(4) adds spacing requirements: labels are required at conduit entry and exit points, at every pull point, above and below every penetration, and every 10 feet on exposed runs.
Here's a scenario Print Pro AZ sees regularly: An installer labels DC conductors at the combiner box and the inverter but skips the intermediate pull box between them. The inspector finds the unlabeled splice and issues a correction notice. The re-inspection costs a day on the schedule and delays the utility interconnection.
Label every connection point. It takes five minutes. A re-inspection doesn't.
What Changed from NEC 2023 to NEC 2026 for Polarity Labeling?
NEC 2023 already required polarity identification for DC conductors under Article 690.31. NEC 2026 tightened the language in two ways.
First, it defined the approved marking text. NEC 2023 required polarity identification but left room for AHJ-to-AHJ interpretation about what exactly that marking had to say. NEC 2026 spells it out: +, POSITIVE, or POS for positive conductors; −, NEGATIVE, or NEG for negative conductors. No more guessing whether your shorthand satisfies the inspector.
Second, it consolidated the insulation color restrictions directly into the polarity marking section. Previously, confirming which insulation colors were off-limits required cross-referencing multiple code sections. NEC 2026 puts the complete rule — required text and forbidden colors — in one place.
The underlying requirement has not changed: identify polarity at every connection point using a permanent, durable method. What NEC 2026 removed is the interpretation zone that led to inconsistent enforcement across jurisdictions.
Bottom line: If you were already labeling DC conductors correctly under NEC 2023, NEC 2026 is a refinement, not a rebuild. If your crew was approximating the label text or relying on ambiguous insulation color choices, NEC 2026 closes those gaps.
Why Polarity Labeling Errors Cause Inspection Failures
Polarity labeling failures cluster into three patterns:
1. Wrong marking text. Using "+" on a permanent label is compliant. Writing a plus sign on masking tape with a marker is not — it's not durable, it won't survive outdoor conditions, and it doesn't meet the NEC's permanence standard.
2. Insulation color conflict. A negative conductor run on red insulation with a "NEG" label still fails. The insulation color restriction applies independently of whatever the label says. Both must comply.
3. Missing labels at intermediate splice points. Most installers label the endpoints — combiner, inverter, disconnect — and miss the pull boxes and conduit bodies between them. Per NEC 690.31, every splice point counts.
Print Pro AZ's NEC-compliant solar label bundles include polarity labels built to NEC 2026 specs — pre-verified for correct text, durable UV-rated material, and sized for common conductor gauges. That removes the guesswork from field labeling entirely.
How to Choose the Right Polarity Marking Method
Three compliant approaches are common in the field:
1. Color-coded insulation — Fastest for factory-wired assemblies. Requires no additional field marking if insulation colors are compliant. Standard on pre-wired microinverter branch circuits.
2. Permanent adhesive labels or marking tape — Best for field-run conductors in conduit. Must show the correct approved text and be rated for outdoor UV exposure and temperature range. Wrap fully around the conductor at each connection point.
3. Heat-shrink sleeving or printed ferrules — Used on smaller-gauge wiring where label wrapping is impractical. Must display the required + or − text. Shrink before final termination to confirm the marking is secure.
Whatever method you use, it must remain readable for the life of the installation. A label that fades after one Arizona summer doesn't meet the NEC permanence standard. Print Pro AZ offers custom-printed solar polarity labels rated for outdoor UV conditions — the same durability standard the NEC's permanence requirement demands.
Is Your State on NEC 2026 Yet?
As of April 2026, most states are still operating under NEC 2023 or earlier editions. Washington State has targeted NEC 2026 adoption by December 31, 2026. Oregon and Minnesota are actively reviewing the 2026 edition.
This affects your polarity labeling in a practical way: if your state runs NEC 2023, the less-prescriptive language governs. If you're in a state moving toward NEC 2026, the explicit text and color rules in Article 690.31(B)(2) are your standard.
When in doubt, label to NEC 2026 specs. Using "+", POSITIVE, or POS and "−", NEGATIVE, or NEG on compliant insulation colors satisfies both editions. No inspector will red-tag an installation for labeling too clearly.
Check your state's current NEC adoption status at the NFPA's NEC enforcement map, or confirm directly with your local AHJ before the permit submittal.
Frequently Asked Questions
Can I use red insulation for my negative DC conductor?
No. NEC 2026 Article 690.31(B)(2) explicitly prohibits red insulation for negative DC conductors in PV systems. Red is permitted for positive conductors only. Using it for negative creates a polarity conflict with other NEC conductor identification conventions.
What are the approved text options for DC conductor polarity labels under NEC 2026?
For positive conductors: the plus sign (+), the word POSITIVE, or the abbreviation POS. For negative conductors: the minus sign (−), the word NEGATIVE, or the abbreviation NEG. All markings must be durably and permanently applied to the conductor insulation or sleeve.
Do I need polarity labels inside junction boxes, or just at the inverter and combiner?
You need polarity identification at every termination, connection, and splice point — including inside junction boxes and pull boxes. NEC 690.31 does not limit this to system endpoints. Missing a splice inside a pull box is one of the most common polarity labeling failures at inspection.
Does NEC 2026 polarity marking apply to grounded conductors?
The explicit +/−/POS/NEG marking requirements in NEC 2026 Article 690.31(B)(2) apply to nonsolidly grounded conductors. Grounded conductors have separate identification requirements under NEC 200.6 and other sections of Article 690.
What makes a polarity marking "permanent" under the NEC?
The NEC requires that conductor identification remain readable for the life of the installation. A label that fades, peels, or smears in outdoor conditions doesn't qualify. Use labels or sleeving rated for UV exposure and the operating temperature range of the PV system.
For a complete overview of solar label requirements under NEC 690, see NEC 690 Labels: Complete Solar Code Requirements Guide.
Conclusion
NEC 2026 Article 690.31(B)(2) gives you a clear framework: identify every ungrounded DC conductor at every connection point, use the exact approved text, and stay off the restricted insulation colors. Following those three rules eliminates one of the most preventable solar inspection failure categories.
Get your DC conductor polarity labels right before the inspector shows up — not after. Print Pro AZ's solar electric label packs include polarity labels built to NEC 2026 specs, UV-rated and ready for field application.
Have a commercial job with complex DC conductor runs? Send us your plan sets and we'll build a label package that covers every connection point.
Questions? Call Brent: (602) 649-5305.
Brent Hanke | Print Pro AZ | (602) 649-5305 | b.hanke@printproaz.com
Brent Hanke is the founder of Print Pro AZ, supplying NEC-compliant labels to contractors across the country.