NFPA 79 Marking Requirements for Industrial Machinery: Nameplates, Disconnects and Device Identification
A machine ships with a UL 508A label inside the panel, but the disconnect out on the frame has no marking, and a service tech can't match a single pilot device on the door to the schematic without guessing. NFPA 79 marking requirements exist to close exactly that gap between the machine and its drawings.
Important Disclaimer
This article is provided for general informational purposes only and does not constitute legal, safety, or professional compliance advice. Regulations, standards, and codes are subject to change and may be interpreted differently by authorities having jurisdiction (AHJ). Always consult with qualified safety professionals, licensed engineers, or legal counsel to determine the specific requirements applicable to your facility. TagBuilder is not responsible for any actions taken based on this information.
What NFPA 79 Covers
NFPA 79, Electrical Standard for Industrial Machinery, is a construction standard for the machine itself — the wiring, control circuits, motors, and enclosures built onto a piece of equipment before it ships, as distinct from the building electrical system it eventually plugs into. Machine builders and integrators design to it because two other documents lean on it directly: NEC Article 670 (Industrial Machinery) points back to NFPA 79 for the machine's supply nameplate data instead of restating it, and UL 508A recognizes NFPA 79 marking practice for panels built as part of a complete machine. If you're building a control panel that ships mounted on a machine rather than sold standalone, NFPA 79's Chapter 16 marking requirements are usually the ones an inspector or integrator's engineer will ask about first.
The Machine Nameplate: What Chapter 16 Requires
NFPA 79's marking chapter calls for a nameplate mounted at or near the machine's main disconnecting means, positioned so it's visible and legible without removing a panel or opening a door. The data on it is meant to answer the questions an installer or inspector needs answered before energizing the machine: what feeds it, how much current it draws, and what fault current it's rated to withstand.
Typical required content includes the supplier's identification, a model or serial designation, the rated supply voltage, phase count and frequency, the machine's full-load current, the largest motor or load current (used to size upstream conductors and overcurrent protection), the short-circuit current rating (SCCR), and a reference to the machine's diagram or drawing number from the technical documentation package. Exact subsection numbers and any additional required fields shift between editions, so confirm the current edition of NFPA 79 with your engineer before finalizing plate copy.
| Field | What belongs on it |
|---|---|
| Supplier | Name and address or other means of identification |
| Model / Serial | Model or type designation, serial number |
| Supply | Rated voltage, number of phases, frequency (e.g. 480V, 3-phase, 60Hz) |
| Full-load current | Total current draw of the machine at rated supply |
| Largest motor or load | Largest single motor or load current, for supply conductor sizing |
| SCCR | Short-circuit current rating the machine is suitable for |
| Control voltage | Control circuit voltage, if different from supply |
| Drawing number | Reference to the schematic set required under Chapter 17 |
Supply Disconnect Identification
Separate from the machine nameplate, the disconnecting means itself has to be marked to show its open and closed positions and, where the machine has more than one, what portion of the machine each one controls. This comes up on machines with a section that has to stay powered for diagnostics or a heated element that runs independent of the main drive — two disconnects, each needing its own clear label so a tech doesn't assume one handle isolates everything. A small legend plate mounted directly above or below the handle, stating what that disconnect feeds, is usually the cleanest way to satisfy this without cluttering the enclosure door.
Warning Markings: Multiple Supply Sources and Retained Voltage
NFPA 79 requires a warning marking where a machine has more than one source of electrical supply, so a technician doesn't open one disconnect and assume the machine is fully de-energized. This applies to machines with a remote or auxiliary feed, a separate welding circuit, or an uninterruptible control section.
A related requirement applies where capacitors, a DC bus, or other components can retain a hazardous voltage after the main disconnect is opened — common on machines with variable frequency drives. The marking needs to warn of the retained voltage and, where practical, state the discharge time before it's safe to work inside the enclosure. Both markings are meant to be read and acted on in seconds, not studied like a manual, so keep the wording short and the plate placed where the door actually opens.
Device and Component Identification
Chapter 16 also governs device-level marking: each electrical component, enclosure, and conductor termination is required to carry a designation that matches the diagrams required under Chapter 17's technical documentation. This is the requirement that lets a tech go from the schematic in the machine's binder to the physical device on the door and back without guessing which relay is which.
A common naming convention looks like this:
- PB1, PB2, PB3 — push buttons, numbered in the order they appear on the schematic
- SS1 — selector switch
- CR1, CR2 — control relays
- M1 — motor
- QS1 — main disconnect switch
- TB1 — terminal block
The designation on the drawing is only useful if it also shows up on the panel. A legend plate mounted under or around each pilot device carrying that same PB1 or SS1 designation — not a generic label like "START" — is what keeps the physical panel matching the print set years after the original build. See the push-button ring tag guide for how that works on 22mm and 30mm devices specifically.
Where NFPA 79 Meets UL 508A and NEC 670
These three documents overlap on purpose but aren't identical. UL 508A governs how an industrial control panel is built and listed, and its Supplement SB covers the SCCR marking that has to appear on the panel. NFPA 79 governs the machine the panel is mounted on or wired into, and its nameplate requirement covers the whole machine's supply data, not just the panel. NEC Article 670 is the installation code's entry point for industrial machinery — rather than restating supply, disconnect, and SCCR marking rules, it generally defers to NFPA 79 for a machine that's built to that standard.
In practice, a panel that's part of a UL 508A listed machine build usually needs its SCCR marking to match what's on the NFPA 79 machine nameplate — a mismatch between the two is a common finding when an integrator's field engineer reviews a new machine. See the UL 508A nameplate guide for what the panel-level marking needs to cover on its own. When in doubt about which document governs a specific plate, ask the machine's listing service or the AHJ rather than guessing.
Durable Marking for a Machine That Gets Washed Down or Runs Hot
NFPA 79 expects markings to stay legible for the life of the machine, which is a meaningfully different bar than legible on the day it ships. A printed or adhesive label on a machine that sits next to an oven, gets sprayed down daily, or vibrates on a conveyor frame is a maintenance problem waiting to happen — ink fades, adhesive lets go, and the tag that mattered most (the disconnect warning, the SCCR plate) is the one nobody can read six months in.
Engraved two-ply plastic holds up better in these environments because the identifier is cut through a colored cap layer into a contrasting core rather than printed on top of a surface — there's no ink to fade and no adhesive bond carrying the legibility. For food-grade washdown, high-heat areas, or outdoor-adjacent installs, engraved stainless is worth the upcharge on the main nameplate and disconnect warning specifically, even if the rest of the device tags stay in plastic. Mechanical fastening (rivets or screws) also holds up better than adhesive-only mounting on a frame that sees real vibration.
Frequently Asked Questions
Does NFPA 79 apply if my panel is already UL 508A listed?
Usually yes, and the two aren't a substitute for each other. UL 508A covers how the control panel itself is built and marked; NFPA 79 covers the machine the panel is mounted on, including the machine-level nameplate and disconnect and device marking. A listed panel built into an NFPA 79 machine still needs the machine-level marking Chapter 16 calls for.
What's the minimum information required on the machine nameplate?
At minimum, expect supplier identification, rated voltage/phase/frequency, full-load current, largest motor or load, SCCR, and a reference to the machine's drawing set. The exact list and any additional fields can vary by edition, so confirm against the current edition of NFPA 79 before finalizing artwork.
Does every pilot device need its own legend plate?
NFPA 79 requires the device identification to match the diagrams, which in practice means every push button, selector switch, and indicator that has a designation on the schematic should carry that same designation on the panel — usually as a legend plate rather than a handwritten label, since it has to stay legible for the machine's service life.
What edition of NFPA 79 should I be designing to?
Use the current edition adopted by your customer's engineering spec or your AHJ. Section numbering and specific required fields have shifted between editions, so don't assume a plate template built against an older edition is current without checking.
Do I still need a warning label if the machine has only one disconnect?
The multiple-supply-source warning specifically applies when there's more than one source feeding the machine. A single-disconnect machine typically doesn't need that particular label, but it may still need a retained-voltage warning if it has a VFD, capacitor bank, or other component that holds a charge after the disconnect opens.
Where does the SCCR marking actually go — the panel or the machine nameplate?
Both, and they need to agree. UL 508A requires it on the panel per its listing; NFPA 79 requires it on the machine nameplate. A mismatch between the two numbers is a common finding during review, so confirm the panel builder and the machine integrator are working from the same fault-current data.
Machine nameplates, disconnect plates and legend plates that match your schematic, engraved to order.
Getting the wording right on paper is only half the job — the plates have to survive the environment the machine actually runs in. Start with the machine nameplate shop for the main supply plate, add matching device tags from the selector and pilot device legend plates, and round out ring-style tags for valves or auxiliary devices from the ring tag shop so every designation on the schematic has a physical match on the machine.
UL, NFPA, NEC, ASME, CEMA, TIA, ANSI and OSHA are names or marks of their respective organizations; TagBuilder is not affiliated with or endorsed by any of them. Requirements above are paraphrased summaries, not the text of any standard. Always work from the current published edition and your AHJ.
