Two reels arrive with the same conductor count, the same jacket compound and the same voltage marking. One may be run from a tray across open space to a machine. The other may not, and nothing about its appearance says so. The difference is two letters printed after the type designation, and they are the whole subject of this article.
That is not a marketing distinction. It is written into the wiring code as a permission, with conditions attached, and the conditions are specific enough to argue about in a submittal review.
A cable type is a list of permissions
NFPA 70 does not organize cable by material so much as by where it may go. Each article follows the same shape: a scope, a definition, a list of uses permitted, a list of uses not permitted, then construction specifications. Read it that way and a type designation stops being a product name. It becomes a bundle of permitted installation methods, and the suffix attached to the type is usually the part that changes which methods are in the bundle.
What the Code says Type TC is
Article 336 covers power and control tray cable, Type TC. Its scope is the use, installation and construction specifications for that cable, and nothing else.
The definition is structural rather than performance-based. Type TC is a factory assembly of two or more insulated conductors, with or without associated bare or covered grounding conductors, under a nonmetallic jacket.
Two consequences follow. The conductor count starts at two, so a single-conductor cable is not Type TC however it is jacketed. And the jacket is nonmetallic by definition: the construction clause states that a metallic sheath or armor is not permitted either under or over it. Metallic shields are permitted, over groups of conductors, under the outer jacket, or both — a shield is not an armor.
So a reel that looks armored is not Type TC, and the distinction matters when the crush and impact question arrives.
The default answer is no
The uses Type TC is permitted for are broad. The places it may be installed are narrower.
Permitted uses | |
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Power, lighting, control and signal circuits | Within the type’s scope |
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In cable trays | The installation the type is named for |
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In raceways | |
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Outdoors, supported by a messenger wire | One of the two exemptions from the tray-or-raceway rule |
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Class 1 circuits | As permitted in Parts II and III of Article 725 |
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Non-power-limited fire alarm circuits | Where conductors comply with 760.49 |
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Industrial establishments, marked TC-ER | The second exemption, covered below |
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Wet locations | Only where also resistant to moisture and corrosive agents |
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The prohibition that gives the article its shape is the second one on the other list: Type TC shall not be installed outside a raceway or cable tray system, except as permitted in the messenger-wire and industrial provisions. Everything else is downstream of that sentence. A tray cable is, by default, a cable that lives in a tray.
Not permitted | |
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Where exposed to physical damage | |
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Outside a raceway or cable tray system | Except the messenger-wire and TC-ER provisions |
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Exposed to direct sunlight | Unless identified as sunlight resistant |
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Direct buried | Unless identified for that use |
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The two letters that buy the exemption
The industrial provision is the one that lets a tray cable leave the tray.
In industrial establishments, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, a Type TC cable may be run between a cable tray and the utilization equipment or device. To do it, the cable has to meet all of the following: it must be continuously supported and protected against physical damage using mechanical protection such as struts, angles or channels; it must comply with the crush and impact requirements of Type MC cable; and it must be identified for the use with the marking Type TC-ER. The cable is then to be secured at intervals not exceeding 1.8 m (6 ft).
Three conditions, each doing separate work. The occupancy condition limits the provision to industrial settings under qualified supervision. The support condition rules out a cable draped through free air. The crush and impact condition is a demand on the cable itself, and it is the reason the suffix exists.
TC-ER is a permission with three conditions
Six feet appears twice and does not mean the same thing
There is an exception to that provision, and it contains the same number.
Where the cable is not subject to physical damage, Type TC-ER may transition between cable trays, and between cable trays and utilization equipment or devices, for a distance not exceeding 1.8 m (6 ft) without continuous support. The cable must still be mechanically supported where it exits the cable tray, so that the minimum bending radius is not exceeded.
Read the two sentences together and the number 1.8 m turns up in both, describing two different things.
The first is a securement interval. It is the spacing between supports along a run, and it applies however long the run is.
The second is a total distance. It is the length of an unsupported transition, and it is an allowance in the opposite direction: it permits a short span with no continuous support at all, because the transition between a tray and a device is awkward to support.
A thirty-foot TC-ER run does not have a thirty-foot unsupported allowance. It needs support at intervals of no more than 6 ft, and if it crosses between two trays, that crossing may be up to 6 ft long without continuous support. The number is identical and the rules are not, which is how a specification ends up quoting the wrong one.
The same 6 ft used as a spacing and as a length
The suffix is a mechanical claim
Notice what the crush and impact condition asks for. Type MC is metal-clad cable, whose mechanical protection comes from a metallic covering, and Type TC is expressly forbidden from having one.
The consequence is that a TC-ER cable has to survive the mechanical duty of an armored product without the armor. That is a construction requirement met in the conductor assembly, the jacket compound and the jacket thickness, not by adding a layer of metal, and it cannot be verified by looking at the reel. The evidence is in the test record.
The same construction appears elsewhere in the Code, which is the clearest sign that it is a deliberate device rather than one article’s preference.
Article | Type | What the exposed-run provision requires |
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336 | Type TC | No metallic sheath or armor, complies with the crush and impact requirements of Type MC cable, identified with the marking Type TC-ER, secured at intervals not exceeding 1.8 m (6 ft) |
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727 | Type ITC | No metallic sheath or armor, complies with the crush and impact requirements of Type MC cable, identified for the use, continuously supported and protected against physical damage, secured at intervals not exceeding 1.8 m (6 ft) |
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725 | Type PLTC, with a metallic sheath or armor | Permitted to be installed exposed where continuously supported and protected against physical damage using mechanical protection such as dedicated struts, angles or channels, secured at intervals not exceeding 1.8 m (6 ft) |
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The wording repeats almost verbatim across three different cable types. Two phrases do most of the work: continuous support with struts, angles or channels, and securement at 6 ft intervals. Where the code will not accept a nonmetallic construction on its own, as with power-limited tray cable, it falls back on the armor instead. Either way the price of an exposed run is the same, and it is paid in support hardware and in securement spacing.
Bending radius is set by the article, not the data sheet
Article 336 also fixes bending radius directly, which is unusual and useful. For Type TC cable without metal shielding the minimum bending radius is four times the overall diameter for cables 25 mm (1 in.) or less, five times for cables larger than 25 mm but not more than 50 mm (2 in.), and six times for cables larger than 50 mm. Type TC cables with metallic shielding take a minimum of twelve times the overall diameter.
That last number is the one to notice. Shielding inside a nonmetallic jacket roughly triples the minimum bend compared with an unshielded cable of the same diameter. The shielded version is not the unshielded version with a screen added; it has a different handling limit and usually a different pulling plan.
Bending radius multipliers by diameter band
Ampacity depends on where the cable is installed
There is one more place where the installation method overrides the product. Ampacity for Type TC is not read from a single table. It is determined in accordance with one reference for conductors 14 AWG and larger, a second reference for 18 AWG through 16 AWG conductors installed in cable tray, and a third reference when the same cable is installed in a raceway or as messenger-supported wiring.
Three routing rules, three sources, one cable. The ampacity of a given construction therefore depends on how it was installed, which means the number in a quotation is only meaningful alongside the installation method it was calculated for.
FAQ
Does TC-ER mean the cable is armored?
No. Type TC is defined by a nonmetallic jacket, and a metallic sheath or armor is not permitted under or over it. The ER suffix requires the cable to meet the crush and impact requirements of Type MC cable, but it must do so without a metallic covering.
Can TC-ER be run unsupported between a tray and a machine?
Only within limits. The exception to the industrial provision permits a transition of up to 1.8 m (6 ft) without continuous support where the cable is not subject to physical damage, with mechanical support at the tray exit so the minimum bending radius is held. Anything longer falls under the main provision, which requires continuous support and securement at intervals not exceeding 1.8 m (6 ft).
Is the 6 ft figure the support spacing or the unsupported length?
Both figures appear, and they are different rules. The securement interval along a supported run is not more than 1.8 m (6 ft). The unsupported transition allowance is a total distance of not more than 1.8 m (6 ft). One is a spacing, the other a length.
Conclusion
A cable type in the wiring code is a set of permitted installation methods, and the suffix attached to the type is usually what changes the set. Type TC carries a nonmetallic jacket, may not have armor, and by default lives in a tray or a raceway.
Add the ER marking and the cable earns a narrow permission to run exposed, but only in an industrial occupancy under qualified supervision, only with continuous mechanical support, and only if the construction meets Type MC crush and impact performance without the metal. The reward is a 6 ft securement interval and, in a transition, a 6 ft unsupported allowance that is a length rather than a spacing.
None of that is visible on the jacket beyond the four characters. It is decided at the construction stage, documented in a test record, and then argued about on site when someone reads the wrong 6 ft.
Industrial and control cable for tray installations
ZONG Cable builds industrial and control cable and can state, before an order, which construction and which marking the cable will carry, so the submittal and the reel agree. Send us the installation method, the conductor count and the mechanical duty, and we will tell you whether the construction you are asking for can carry the marking you need. The wider range sits under cable, the industrial families are covered in the guide to industrial flexible cable, pathway support and fill are set out in the guide to J-hook spacing and cable tray fill, the evidence that travels with a batch is explained under test report validity, and industrial Ethernet and M12 covers the data side of the same plant. If a specification names a marking your reel does not carry, send us the clause before the cable is built.
Sources
- NFPA 70, National Electrical Code, 2011 edition, Article 336, Power and Control Tray Cable: Type TC. Read directly for this article: 336.1 Scope; 336.2 the definition of power and control tray cable, Type TC, as a factory assembly of two or more insulated conductors, with or without associated bare or covered grounding conductors, under a nonmetallic jacket; 336.10 Uses Permitted, all eight provisions, including the messenger-wire provision, the industrial provision requiring continuous support and protection against physical damage using mechanical protection such as struts, angles or channels together with compliance with the crush and impact requirements of Type MC cable and identification with the marking Type TC-ER, the securement interval of 1.8 m (6 ft), the equipment grounding conductor requirement and its treatment for conductors 6 AWG or smaller, and the wet-location condition; the exception permitting a Type TC-ER transition between cable trays and between cable trays and utilization equipment or devices for a distance not exceeding 1.8 m (6 ft) without continuous support, with mechanical support at the tray exit to hold the minimum bending radius; 336.12 Uses Not Permitted, all four provisions including the prohibition on installation outside a raceway or cable tray system except as permitted in 336.10(4) and 336.10(7); 336.24 Bending Radius, both the unshielded multipliers of four, five and six times overall diameter by diameter band and the twelve-times minimum for cables with metallic shielding; 336.80 Ampacity, including the three separate determination references for conductors 14 AWG and larger, for 18 AWG through 16 AWG conductors installed in cable tray, and for installation in a raceway or as messenger-supported wiring; 336.100 Construction, including the prohibition on a metallic sheath or armor under or over the nonmetallic jacket and the permitted placement of metallic shields; 336.104 Conductors; 336.116 Jacket; and 336.120 Marking. Full text published by Public.Resource.Org. https://archive.org/details/gov.law.nfpa.nec.2011
- NFPA 70, National Electrical Code, 2011 edition, Article 727, Instrumentation Tray Cable: Type ITC, at 727.5 Uses Permitted. Read directly for this article: provision (5), permitting cable without a metallic sheath or armor that complies with the crush and impact requirements of Type MC cable and is identified for such use to be installed exposed, continuously supported and protected against physical damage using mechanical protection such as dedicated struts, angles or channels, and secured at intervals not exceeding 1.8 m (6 ft). https://archive.org/details/gov.law.nfpa.nec.2011
- NFPA 70, National Electrical Code, 2011 edition, Article 725, Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits, at 725.154(D) Industrial Establishments. Read directly for this article: provision (2), permitting Type PLTC cable with a metallic sheath or armor to be installed exposed, continuously supported and protected against physical damage using mechanical protection such as dedicated struts, angles or channels, and secured at intervals not exceeding 1.8 m (6 ft). https://archive.org/details/gov.law.nfpa.nec.2011
