Most people read the writing on a cable jacket exactly once, and it is usually while something has already gone wrong. The installer is holding a cut length, the inspector wants to know what it is, and the print that was ignored on the reel is suddenly the only evidence available.
It is not decorative. The information printed along a cable is a regulated identification system with required contents, required repeat intervals and different rules for different constructions. Two of its features are genuinely counterintuitive, and one of them matters a great deal if you buy cable with your own brand on it.
The five things that have to be there
The marking requirements for conductors and cables sit in Article 310 of the National Electrical Code, and the 2011 edition states them plainly. All conductors and cables shall be marked to indicate five things:
Required item | What it covers |
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The maximum rated voltage | The voltage the insulation is rated for |
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The proper type letter or letters | The type designation for the wire or cable type as specified elsewhere in the code |
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The manufacturer’s name, trademark, or other distinctive marking | Wording that lets the organization responsible for the product be readily identified |
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The AWG size or circular mil area | Conductor size, with a note pointing to the conductor properties table in Chapter 9 for area in SI units |
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A note where the neutral is smaller than the ungrounded conductors | Applies to cable assemblies where that is the case |
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Read the third item twice, because it is doing more work than it looks. The requirement is not "print the factory name." It is that the organization responsible for the product must be readily identifiable from the marking. That is an accountability clause wearing the clothes of a labeling rule, and it is the one that governs what can and cannot appear on a private-label jacket.
Two different repeat intervals
The marking is not printed once. It is repeated along the length, and here is the first counterintuitive detail: not everything repeats at the same interval.
For the cable types listed in the surface-marking rule, the AWG size or circular mil area must be repeated at intervals not exceeding 610 mm, which is 24 inches. All other markings must be repeated at intervals not exceeding 1.0 m, which is 40 inches.
Marking | Maximum interval |
|---|
AWG size or circular mil area | 610 mm (24 in.) |
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Everything else | 1.0 m (40 in.) |
|---|
The size appears roughly twice as often as the rest, and the reason is practical rather than aesthetic. Size is the one item an installer checks most often, often on a cut end or a partially consumed reel where only a short run of print is visible. The other information is looked for once and recorded.
That difference shows up in purchase orders as a specification line, and it is worth knowing which numbers you are quoting. Note also the form the code gives both values in: the metric figure first, the inch figure in parentheses. Both are canonical, so there is nothing to convert. When a specification quotes an interval it should quote one of the two as written, because 24 inches converts to 609.6 mm, and a specification that says 609 mm has tightened a maximum for no reason.
Not every cable carries its marking on the jacket
The second counterintuitive detail is that surface marking is not universal. The code provides three methods, and which one applies depends on the construction.
Method | How it works | Applies to |
|---|
Surface marking | Printed durably on the outer surface at the intervals above | Single-conductor and multiconductor rubber- and thermoplastic-insulated wire and cable, nonmetallic-sheathed cable, service-entrance cable, underground feeder and branch-circuit cable, tray cable, irrigation cable, power-limited tray cable, instrumentation tray cable |
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Marker tape | A tape located inside the cable, running for its complete length | Metal-covered multiconductor cables, with exceptions for Type MI and Type AC, and a permitted alternative for Type MC, Type ITC and Type PLTC cable |
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Tag marking | A printed tag attached to the coil, reel or carton | Type MI cable, switchboard wires, metal-covered single-conductor cables, Type AC cable |
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So a run of metal-covered multiconductor cable can carry everything it is required to carry on a tape inside it, and four cable types carry their identification on the packaging rather than the product. If you are inspecting an incoming shipment and cannot find print on the jacket, the correct next step is to read the code section for that construction rather than to assume the cable is unmarked.
There is one more variation worth knowing. For six listed multiconductor cable types, the wire-size information may optionally be marked on the surface of the individual insulated conductors rather than only on the overall assembly.
Type letters encode construction
The type letters are not a quality grade or a generation number. They encode what the cable physically is, and the suffixes carry real information.
A type letter used alone indicates a single insulated conductor. Where a suffix appears, it means a specific arrangement of conductors inside a covering: D indicates two insulated conductors laid parallel within an outer nonmetallic covering, and M indicates an assembly of two or more insulated conductors twisted spirally within an outer nonmetallic covering.
Designation | Construction |
|---|
Type letter alone | A single insulated conductor |
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Type letter with D | Two insulated conductors laid parallel inside an outer nonmetallic covering |
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Type letter with M | Two or more insulated conductors twisted spirally inside an outer nonmetallic covering |
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That is why the type string on a jacket is worth reading properly. It tells you the construction arrangement, not just the material family.
What a jacket is required to carry, at what repeat interval, and which of the three marking methods applies
"Durable" is a requirement without a test
Every one of the surface-marking rules uses the word durable. The code requires the marking to be durable and does not define the term, and for cable it does not attach a duration to it either.
That is the actual answer to the question every buyer eventually asks about print that has rubbed off or faded. The code sets a durability requirement and leaves the definition of durability to the product listing — the recognized standard for the cable type and the testing that supports it. The code text is not the test method, and reading it will not tell you how long the print is expected to last.
The code does apply duration-based thinking elsewhere, which makes the contrast sharp. In the article covering rigid PVC conduit, each length must be clearly and durably marked at least every 3 m, and the required permanence is graded by where the product goes: for conduit recognized for use aboveground, the markings must be permanent, while for conduit limited to underground use the markings need only be sufficiently durable to remain legible until the material is installed.
Product and application | What the marking durability has to achieve |
|---|
Cable, surface marked | Durable, with no duration attached in the code text |
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Conduit recognized for use aboveground | Permanent |
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Conduit limited to underground use only | Legible until the material is installed |
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Durability graded by how long it needs to survive is a sensible rule. For cable, the code states the requirement and stops there, which means the practical answer to "how durable is durable" has to come from the product standard and from the supplier’s own testing.
The optional markings deserve a mention here too, because they are where material behavior is declared. Conductors and cables in Chapter 3 may be surface marked to indicate special characteristics of the cable materials, including limited smoke and sunlight resistance. Those are not decoration either: in application contexts where a product must be sunlight resistant, the requirement is that it be listed and marked as such. An optional marking in one article becomes an enforced one in another, and the jacket is where it is recorded.
How three different constructions carry the same required information, and where each one puts it
What this means for a private-label order
If you are buying cable with your own brand printed on it, the accountable-marking clause is the one to think about hardest, because it is the junction between marketing and liability.
The requirement is that the organization responsible for the product be readily identifiable from the marking. A brand name is a distinctive marking, so a private-label print satisfies the form of the requirement — provided that the mark actually leads to the responsible organization. That is the question to settle in writing before the print rollers are made, and the answer is not always obvious when the product is manufactured by one party, sold under a second party’s brand, and distributed by a third.
Four specification items carry most of the risk:
- The exact string, character for character, including spacing, the type designation and the voltage.
- The repeat intervals, because the size and everything else do not share one number.
- The method, since surface marking, an internal marker tape and a tag are not interchangeable and depend on the construction.
- What is supposed to happen to the print in service, which is the durability question the code deliberately leaves to the product standard.
Get those four into the drawing and the marking stops being a nuisance at goods-in and becomes what it was designed to be: the identification of the product, on the product, for the life of the installation.
Marking durability as the code grades it, from cable at the open end of the scale to conduit whose marking only has to survive until installation
FAQ
What does the print on a cable jacket have to include?
For conductors and cables covered by Article 310, five items: the maximum rated voltage, the type letter or letters, the manufacturer’s name or other distinctive marking identifying the organization responsible, the AWG size or circular mil area, and a note where a cable assembly has a neutral smaller than its ungrounded conductors.
How often must the marking be repeated?
The AWG size or circular mil area must be repeated at intervals not exceeding 610 mm or 24 inches. All the other required markings must be repeated at intervals not exceeding 1.0 m or 40 inches. The two intervals are different, and both are maximums rather than targets.
Is the print always on the jacket?
No. Metal-covered multiconductor cables use a marker tape inside the cable running its full length, and Type MI cable, switchboard wires, metal-covered single-conductor cables and Type AC cable are marked by a printed tag on the coil, reel or carton. Surface marking applies to a specific list of cable types rather than to everything.
Why did the print rub off, and does it matter?
The code requires surface marking to be durable and does not define durability or attach a duration to it for cable, so the practical standard comes from the product listing and the supplier’s testing rather than from the code text. Where print has become illegible, the identification requirement has failed in service, which is a legitimate question to put to the supplier.
Conclusion
The print on a jacket is a small, cheap, easily ignored feature that carries a legal identification function. It has required contents, and one of them puts the name of the responsible organization on the product. It repeats on two different intervals. It is not always on the jacket at all. And its durability is required but not measured in the code, which is why the answer to "how long should this last" comes from the product standard rather than the text.
Read it once before you need it.
Cable marking and private-label printing
ZONG Cable prints HDMI, USB, network, patch cord, fiber and communication cable to the marking scheme each customer specifies, and can produce private-label jackets carrying a buyer’s brand alongside the identification a listing requires. If you are setting up marking for a new part number, send us the exact string, the type designation, the voltage, the repeat intervals you need and the construction it will be printed on, and we will confirm what the line can run and where the durability question has to be answered by testing. The range sits under cable, the routines behind each batch are on our test and inspection page, and OEM support covers private-label printing and packaging.
Sources
- NFPA 70, National Electrical Code, 2011 edition, Article 310.120 Marking, including 310.120(A) Required Information, 310.120(B) Method of Marking with surface marking, marker tape and tag marking provisions, 310.120(C) Suffixes to Designate Number of Conductors, and 310.120(D) Optional Markings. Full text published by Public.Resource.Org. https://archive.org/details/gov.law.nfpa.nec.2011
- NFPA 70, National Electrical Code, 2011 edition, Article 352.120 Marking, permanence graded for aboveground and underground conduit. https://archive.org/details/gov.law.nfpa.nec.2011
- ZONG Cable range. https://zh-zong.com/cable/
- ZONG Cable test and inspection. https://zh-zong.com/test-inspection/
