Answer Capsule: High voltage labels are required by NEC 110.34(C) on any entrance to a room or enclosure containing exposed live parts operating above 1,000 volts. The required text is "DANGER-HIGH VOLTAGE-KEEP OUT." Labels must also meet the field-applied hazard marking rules in NEC 110.21(B) and ANSI Z535.4.
Pulling a permit on a medium-voltage job and realizing you have no idea which labels go where is a rough spot to be in. An inspector who opens a switchgear room door and finds missing or non-compliant signage can fail the job on the spot. High voltage equipment carries real consequences when labeling is wrong: failed inspections, OSHA citations, and liability exposure if a worker is injured near an unmarked enclosure. This guide covers exactly what the NEC and OSHA require for high voltage labels, where each label goes, what it has to say, and how to stay compliant on commercial and industrial jobs. By the end, you will know which code sections apply and what to order before your next job walks.
What Voltage Is Considered "High Voltage" Under NEC and OSHA?
The NEC and OSHA use different thresholds, and that gap trips up a lot of electricians.
Under the NEC (NFPA 70), the threshold is 1,000 volts AC or 1,500 volts DC. Article 100 draws the line there, and all of Part III in Article 110 (sections 110.30 through 110.41) applies to equipment operating above that level. In the 2023 NEC, the old Article 490 covering equipment over 1,000V was reorganized into Article 495, now titled "Equipment Over 1,000 Volts AC, 1,500 Volts DC, Nominal." If you are using the 2023 code cycle, look for Article 495, not 490.
OSHA uses a less consistent threshold. Under 29 CFR 1910.303, some provisions treat anything above 600 volts as high voltage, while other sections (such as 1910.304(g)(9)) reference the 1,000-volt mark. CAL/OSHA and several OSHA subpart references treat 600 volts as the high voltage line. The practical takeaway: if your system runs above 600 volts, treat it as high voltage for OSHA purposes. If it is above 1,000V AC, the full NEC high voltage article applies.
| Standard | High Voltage Threshold |
|---|---|
| NEC (NFPA 70) | Over 1,000V AC / 1,500V DC |
| OSHA General Industry (most provisions) | Over 600V |
| OSHA 1910.304(g)(9) | Over 1,000V |
| CAL/OSHA Title 8 | Over 600V |
| ANSI Z535.4 | Governs label design at all voltages |
What Does NEC 110.34 Require for High Voltage Warning Signs?
NEC 110.34(C) is the section you need to know cold. It states that the entrance to all buildings, vaults, rooms, or enclosures containing exposed live parts or exposed conductors operating at over 1,000 volts shall be kept locked unless under the observation of a qualified person at all times.
Beyond the lock requirement, 110.34(C) also mandates a permanent and conspicuous warning sign at every entrance. The code specifies the exact wording: "DANGER-HIGH VOLTAGE-KEEP OUT." That is not a suggestion. That is the language the NEC requires. You cannot substitute "Warning" for "Danger" or use different phrasing and expect to pass an inspection.
Those signs must also comply with NEC 110.21(B), which governs field-applied hazard markings. Per 110.21(B)(1) through (3), labels must use effective words, colors, and symbols to adequately warn of the hazard. The NEC also references ANSI Z535.4 (Product Safety Signs and Labels) as the design standard for those markings. That means a red "DANGER" header, white text on a black lower panel, and the appropriate electrical hazard symbol.
Inspection Tip: If your switchgear has removable access panels on the back, each panel needs its own "DANGER-HIGH VOLTAGE-KEEP OUT" label. One label on the front door is not enough. Per NEC 110.34(C), every entrance point to exposed live parts above 1,000V needs the sign. An inspector who checks the back panels and finds nothing will write it up.
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What Does NEC Article 495 (Formerly 490) Require for High Voltage Enclosures?
Article 495 of the 2023 NEC picks up where 110.34 leaves off. It covers all energized switching and control equipment operating above 1,000V AC or 1,500V DC.
Per Article 495, all energized switching and control parts shall be enclosed in grounded metal cabinets or enclosures. Those enclosures shall be marked "DANGER-HIGH VOLTAGE-KEEP OUT" and locked so that only authorized, qualified persons can enter. The label requirements again point back to 110.21(B) for design compliance. This applies to fixed switchgear, motor control centers, transformers, and mobile high-voltage equipment on job sites.
Article 495 also covers isolating switches. Any isolating switch that is not interlocked with an approved circuit-interrupting device must have a warning sign specifically prohibiting the operator from opening it under load. This is a separate label from the "DANGER-HIGH VOLTAGE-KEEP OUT" sign. It is a procedural warning, and it must also comply with 110.21(B).
For solar installations, DC systems that reach or exceed 1,500V DC now fall under Article 495 in the 2023 NEC. Utility-scale and commercial solar arrays with string voltages above 1,500V DC need the same high-voltage enclosure labels as any AC high-voltage switchgear. Print Pro AZ stocks labels for both AC and DC high-voltage systems, including solar high voltage labels for utility-scale arrays.
How Do OSHA Requirements for High Voltage Labeling Work?
OSHA's electrical labeling requirements sit primarily in 29 CFR 1910.303 and the broader Subpart S electrical standards. Under 1910.303(e), all electrical equipment must be marked with the manufacturer's identification and ratings including voltage, current, and wattage. Those markings must be durable enough to survive the environment where the equipment operates.
For high voltage work areas, OSHA requires conspicuous warning signs at all entrances to rooms or guarded locations containing exposed live parts. The language OSHA uses mirrors NEC 110.34: the sign must prohibit entry by unqualified persons. OSHA also requires that high-voltage equipment be physically separated from lower-voltage systems and that unqualified workers cannot access the area without a barrier or security control.
On construction sites, OSHA 29 CFR 1926.960 governs work on or near exposed energized parts above 50 volts. It requires employers to ensure workers know the nominal system voltage and that proper approach boundaries and PPE are in place. While this section applies more to field work than labeling, it reinforces the baseline rule: every worker who can access or pass near a high-voltage system needs to be warned.
OSHA citations for missing or inadequate high-voltage labels fall under Subpart S violations. These can be classified as serious violations carrying fines up to $16,550 per violation (as of 2026 penalty levels). The fix is straightforward: proper labels before the system is energized. Print Pro AZ supplies durable, OSHA-compliant electrician labels for panels, disconnects, and enclosures across all voltage classes.
What Are the Physical Requirements for High Voltage Labels?
A label that says the right words but fails on materials or design can still draw a citation. Here is what the code and standards require for the physical label itself.
NEC 110.21(B) requires the label to use effective words, colors, and symbols. That points directly to ANSI Z535.4, which defines the design language for safety labels. For a "DANGER" level label, the standard requires:
- A red safety alert header panel
- The word "DANGER" in white or black text on the red panel
- A black lower message panel with white text
- The electrical hazard symbol (lightning bolt in a triangle) where applicable
- Letter height proportional to viewing distance
Labels must also be durable enough for the environment. For outdoor equipment, switchgear vaults, or any installation exposed to moisture, UV, or temperature extremes, that means UV-resistant polyester or vinyl with aggressive adhesive. Paper labels do not cut it on high-voltage enclosures.
| Label Requirement | Governing Standard |
|---|---|
| Required text: "DANGER-HIGH VOLTAGE-KEEP OUT" | NEC 110.34(C) |
| Label design: words, colors, symbols | NEC 110.21(B) |
| Color and symbol standards | ANSI Z535.4 |
| Manufacturer ID and voltage rating on equipment | OSHA 29 CFR 1910.303(e) |
| Isolating switch warning label | NEC Article 495 |
| Arc flash warning label | NEC 110.16 |
| Durability for environment | OSHA 29 CFR 1910.303(e)(1) |
Print Pro AZ produces high voltage labels on industrial-grade polyester with permanent adhesive rated for outdoor and high-temperature environments. Every label is printed to ANSI Z535.4 color and symbol specs. View options for commercial and high-voltage jobs.
Do You Need Arc Flash Labels in Addition to High Voltage Labels?
Yes. These are two separate requirements that apply to the same equipment.
NEC 110.16 requires an arc flash warning label on switchboards, switchgear, panelboards, industrial control panels, meter socket enclosures, and motor control centers that are likely to require examination, adjustment, servicing, or maintenance while energized. The label must warn qualified persons that an arc flash hazard exists. For equipment over 1,000V, this applies alongside the 110.34(C) "DANGER-HIGH VOLTAGE-KEEP OUT" sign.
NFPA 70E goes further and requires the label to include incident energy level or arc flash PPE category, working distance, nominal system voltage, and arc flash boundary. These calculations typically require an arc flash study. The NEC 110.16 label is a minimum warning; NFPA 70E defines the full labeling requirement for energized work.
In practice, your high-voltage switchgear needs at least two labels: the "DANGER-HIGH VOLTAGE-KEEP OUT" sign on every entrance per NEC 110.34(C), and an arc flash warning label on the equipment front per NEC 110.16. If you are doing work under NFPA 70E, the arc flash label needs the full incident energy data.
Real Scenario: A commercial electrician in Phoenix installs a 4,160V switchgear lineup for an industrial client. The inspector checks for three things at final: the "DANGER-HIGH VOLTAGE-KEEP OUT" label on each access door (NEC 110.34(C)), the arc flash warning label on the equipment face (NEC 110.16), and the isolating switch warning label if any non-interlocked isolating switches are present (NEC Article 495). Missing any one of those is a failed inspection. Print Pro AZ can supply all three label types in one order.
FAQ
What does a high voltage label have to say under NEC code?
Per NEC 110.34(C), the required wording is "DANGER-HIGH VOLTAGE-KEEP OUT." This exact language is mandated at every entrance to a room, vault, enclosure, or building containing exposed live parts operating above 1,000 volts. Substituting "Warning" for "Danger" or using different phrasing does not satisfy the code requirement.
At what voltage does the NEC require a high voltage warning label?
The NEC requires high voltage warning labels on equipment and enclosures containing exposed parts operating above 1,000 volts AC or 1,500 volts DC. These thresholds are established in Article 100 and applied through NEC 110.34(C) and Article 495.
Does OSHA require high voltage labels?
Yes. Under 29 CFR 1910.303 and the broader OSHA Subpart S electrical standards, employers must mark entrances to rooms containing exposed live parts with conspicuous warning signs prohibiting entry by unqualified persons. OSHA also requires all electrical equipment to carry manufacturer identification and voltage ratings that are durable enough for the installation environment.
Can I use any label material for high voltage signs?
No. NEC 110.21(B) requires the label to use effective words, colors, and symbols, and the referenced standard ANSI Z535.4 defines specific design requirements including color (red "DANGER" panel), symbols, and text. For outdoor or harsh environments, OSHA 29 CFR 1910.303(e)(1) requires markings durable enough to withstand the environment. Paper or standard office labels are not appropriate for outdoor switchgear or industrial environments.
Do solar DC systems need high voltage labels?
Yes, if string voltage exceeds 1,500 volts DC. The 2023 NEC updated Article 495 to cover systems "Over 1,000 Volts AC, 1,500 Volts DC, Nominal." Utility-scale and commercial solar arrays with DC string voltages above 1,500V now fall under the same high-voltage enclosure labeling requirements as AC switchgear. All enclosures must be marked "DANGER-HIGH VOLTAGE-KEEP OUT" and comply with NEC 110.21(B).
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Conclusion
Three things to take away from this post:
- NEC 110.34(C) requires exact language. "DANGER-HIGH VOLTAGE-KEEP OUT" is not optional wording. It is the code-specified text for every entrance to a space with exposed parts above 1,000V. Every door. Every access panel. Every removable cover.
- OSHA and NEC thresholds differ. OSHA treats 600V as the practical high-voltage line in most general industry standards. NEC draws the line at 1,000V AC and 1,500V DC. On any job above 600V, treat both sets of requirements as active.
- High voltage labels and arc flash labels are separate requirements. NEC 110.34(C) covers entrance signage. NEC 110.16 covers arc flash warning labels on the equipment face. You need both.
Print Pro AZ supplies NEC 110.34(C)-compliant "DANGER-HIGH VOLTAGE-KEEP OUT" labels, arc flash warning labels, isolating switch warning labels, and full electrician label packs for commercial and industrial jobs. Every label is printed to ANSI Z535.4 specs on industrial-grade polyester stock.
Shop our electrician label packs for NEC-compliant high voltage labels
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.
Last Updated: 2026-09-23
This article is part of the Print Pro AZ arc flash labeling series. Start with the pillar guide: Arc Flash Labels: NFPA 70E 2024 Requirements Guide.
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