14.2 System Labeling and Signage Requirements

System Labeling and Signage Requirements

Photovoltaic power systems present unique electrical hazards that differ significantly from conventional alternating-current (AC) building electrical systems. Because solar arrays generate high-voltage direct-current (DC) power whenever sunlight strikes the module surface—power that cannot be shut off simply by tripping an AC circuit breaker—clear, durable, and standardized safety signage is paramount. First responders, emergency personnel, utility linemen, and service technicians rely on visible warning placards to identify energized conductors, locate isolation disconnects, understand rapid shutdown boundaries, and prevent fatal electric shock or arc-flash injuries.

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1. Physical Construction and Durability Standards (ANSI Z535 & UL 969)

System labels must withstand 25 or more years of continuous outdoor environmental exposure, including intense ultraviolet (UV) radiation, freezing temperatures, windblown dust, rain, and humidity. NEC 110.21(B) requires warning labels to be permanently affixed, not handwritten (except for variable information), and durable enough for the environment, so paper labels and handwritten tape do not comply.

Material and Attachment Specifications

• UL 969 (Standard for Marking and Labeling Systems): Many outdoor adhesive labels are recognized under UL 969 for exposure to weather, heat, moisture, and UV light. The NEC does not require UL 969 by name, but the label must suit the environment.
• Placard Construction: High-quality installations utilize engraved phenolic plastic (two-layer micro-surfaced acrylic/phenolic where the top layer is engraved to reveal a contrasting core) or anodized metal placards (photo-anodized aluminum with sealed image layers).
• Attachment Methods: While high-bond acrylic foam adhesives (such as 3M VHB) are accepted on clean, smooth, powder-coated enclosures, outdoor placards should be secured using mechanical fasteners—including stainless steel pop rivets, tamper-resistant machine screws, or UV-resistant outdoor cable ties on raceways. Fasteners prevent placards from falling off during building fires or seasonal thermal cycling.

ANSI Z535 Safety Sign Standards

NEC labeling guidelines incorporate the ANSI Z535 standards for safety signs and colors, which establish a strict hierarchy of signal words:

• DANGER: Indicates an imminently hazardous situation that, if not avoided, will result in death or serious injury. Reserved for high-voltage utility switchgear or high-hazard electrical enclosures.
• WARNING: Indicates a potentially hazardous situation that, if not avoided, could result in death or serious injury. Used for PV system disconnects, energized DC circuits, and backfeed breakers.
• CAUTION: Indicates a potentially hazardous situation that, if not avoided, may result in minor or moderate injury, or equipment damage. Used for operating instructions or multiple source notifications.
• Visual Formatting: Signal words must appear in bold uppercase letters inside a colored header box (e.g., black text inside an orange header for WARNING; white text inside a red header for DANGER). Letters must be contrasted sharply against the background (e.g., white letters on red, or black letters on yellow or orange).

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2. Main Service Disconnect and Dual Power Source Placards

When a photovoltaic system is interconnected with a premises electrical system, the building contains multiple sources of electrical power. Technicians working on service equipment must be alerted that opening the main utility breaker does not de-energize equipment backfed by the solar system.

Dual Power Source Warning (NEC 705.10 / NEC 690.54)

A permanent plaque or directory must be placed at the main service disconnect and all points of interconnection:

• NEC 705.10 Directory Requirement: A permanent plaque or directory must be installed at each service equipment location denoting the presence and physical location of all electric power sources (utility grid, solar PV system, energy storage system, or standby generator) on the premises.
• Dual Source Warning Text:

  WARNING: DUAL POWER SOURCES
  SECOND SOURCE IS PHOTOVOLTAIC SYSTEM
  DISCONNECT BOTH SOURCES BEFORE SERVICING
  

• Point of Interconnection Identification (NEC 690.54): All interactive system points of connection with other sources must be marked at an accessible location at the disconnecting means with the rated AC output current and the nominal operating AC voltage.
• PV System Disconnect (NEC 690.13(B)): Marked "PV SYSTEM DISCONNECT" or equivalent. Where the line and load terminals can both be energized in the open position, add: "WARNING – ELECTRIC SHOCK HAZARD – TERMINALS ON THE LINE AND LOAD SIDES MAY BE ENERGIZED IN THE OPEN POSITION."
• ESS Disconnect (NEC 706.7(D)): Marked with the nominal ESS voltage, the maximum available short-circuit current, the clearing time or arc duration, and the date of the calculation (or an arc-flash label applied per industry practice).

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3. DC PV Power Source Label (NEC 690.53)

The 2017 NEC 690.53 requires the installer to provide a permanent label for the dc PV power source at the dc PV system disconnecting means and at each dc equipment disconnecting means required by 690.15. Where a disconnect serves more than one dc PV power source, the values are listed for each source. The label shows:

1. Maximum Voltage: The maximum PV system voltage calculated per 690.7, corrected for the lowest expected ambient temperature.
2. Maximum Circuit Current: The maximum current calculated per 690.8(A), such as 125% of the sum of the parallel module short-circuit currents.
3. Maximum Rated Output Current of the Charge Controller or DC-to-DC Converter, if one is installed.

DC PV POWER SOURCE
--------------------------------------------
MAXIMUM VOLTAGE:                     462.5 V
MAXIMUM CIRCUIT CURRENT:              23.0 A
MAX RATED OUTPUT CURRENT OF CHARGE
CONTROLLER OR DC-DC CONVERTER:      NOT USED

Edition note: The 2014 NEC 690.53 also required the rated maximum power-point current and voltage, and many older study materials still list them; the 2017 NEC dropped those values. The 2020 NEC reduced 690.53 to a maximum-voltage label, which the 2023 NEC moved to 690.7(D).

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4. Rapid Shutdown Identification and Equipment Signage (NEC 690.56(C))

NEC 690.12 mandates rapid shutdown of rooftop PV systems to protect emergency responders from electric shock when operating on roofs. NEC 690.56(C) dictates standardized visual plaques to inform firefighters whether rapid shutdown controls conductors inside the array boundary:

Rapid Shutdown Type Labels (690.56(C)(1))

690.56(C)(1)(a): Array and Conductors Leaving It Shut Down

Title in capitals at least 3/8 inch high, black on yellow; remaining text black on white, at least 3/16 inch:

SOLAR PV SYSTEM IS EQUIPPED WITH RAPID SHUTDOWN
TURN RAPID SHUTDOWN SWITCH TO THE "OFF" POSITION
TO SHUT DOWN PV SYSTEM AND REDUCE SHOCK HAZARD IN ARRAY.

690.56(C)(1)(b): Only Conductors Leaving the Array Shut Down

The same title in capitals at least 3/8 inch high, white on red; remaining text black on white:

SOLAR PV SYSTEM IS EQUIPPED WITH RAPID SHUTDOWN
TURN RAPID SHUTDOWN SWITCH TO THE "OFF" POSITION
TO SHUT DOWN CONDUCTORS OUTSIDE THE ARRAY.
CONDUCTORS IN ARRAY REMAIN ENERGIZED IN SUNLIGHT.

Both labels include a simple building diagram; the (1)(b) version shows the array area that stays energized. Where a building has PV systems with both rapid shutdown types, or one system without rapid shutdown, 690.56(C)(2) requires a roof plan showing each system, with a dotted line around the areas that remain energized after the rapid shutdown switch is operated.

Rapid Shutdown Switch Label (690.56(C)(3))

The rapid shutdown switch must have a label on it or within 3 feet (1 m) of it reading:

RAPID SHUTDOWN SWITCH FOR SOLAR PV SYSTEM

The label must be reflective, with capital letters at least 3/8 inch high in white on a red background.

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5. DC Raceway and Enclosure Labeling (2017 NEC 690.31(G)(3) and (G)(4))

Because dc PV circuits cannot be de-energized from the building's ac panel, firefighters cutting into walls or roofs need clear warnings. The 2017 NEC requires wiring methods and enclosures containing PV system dc circuits to be marked:

• Wording: WARNING: PHOTOVOLTAIC POWER SOURCE, by permanently affixed labels or other approved permanent marking.
• What Gets Marked: Exposed raceways, cable trays, and other wiring methods; covers or enclosures of pull boxes and junction boxes; and conduit bodies in which any of the available openings are unused.
• Format: Labels must be visible after installation and reflective, with all capital letters at least 3/8 inch (9.5 mm) high in white on a red background, and suitable for the environment.
• Spacing: Labels must appear on every section of the wiring system that is separated by enclosures, walls, partitions, ceilings, or floors, with no more than 10 feet (3 m) between labels or markings.

The 2020 NEC moved this rule to 690.31(D)(2) and also permits the wording "SOLAR PV DC CIRCUIT."

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6. Point of Interconnection Busbar Warnings and Directory Maps

Backfeed Breaker Warning (2017 NEC 705.12(B)(2)(3)(b))

When a solar PV system interconnects on the load side of a panelboard busbar under the 120% rule, the solar circuit breaker must be positioned at the opposite end of the busbar from the utility main breaker. Moving this breaker to the center of the panel could subject the busbar to severe localized overcurrent. To prevent this, a permanent warning label must be installed immediately adjacent to the solar backfeed breaker:

WARNING: POWER SOURCE OUTPUT CONNECTION
DO NOT RELOCATE THIS OVERCURRENT DEVICE

Main Service Directory Plaque (NEC 705.10)

Every building with on-site generation requires a permanent directory plaque at the electrical service entrance. The plaque must provide a graphic site map or clear text detailing the physical location of the main service disconnect, the solar PV system disconnects, battery energy storage disconnects, and any standby generators.

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7. System Labeling Specification Matrix

The following matrix summarizes the required warning labels, placards, physical characteristics, and installation locations across a code-compliant solar installation: