National Electrical Code ExplanationsBased on the 2014 NEC
National Electrical Code Tips: Article 727, Instrumentationa Tray Cable: Type ITC
- From the title, you would think this Article belongs in Chapter 3. After all, isn't Instrumentation Tray Cable (being a cable) a wiring method? What's going on is ITC is a very special type of cable. It doesn't conduct power. It's a signal cable. It operates at under 150V and at 5A or less [727.1]. And it's used strictly with instrumentation and control circuits.
- Type ITC cable is a factory assembly of two or mor insulated conductors enclosed in a metallic sheath; it may (or may not) have a grounding conductor [727.2].
- Interestingly enough, Article 727 follows a format similar to that used for Chapter 3 Wiring methods such as types of cables. That does make sense, considering this is a type of cable. So, as with those other Articles, you will find "Uses Permitted" and "Uses Not Permitted."
- Among the nine permitted uses for Type ITC Cable, you can run it in cable tray. That seems obvious, given the name of this cable type. You can also run it in raceways [727.4].
- It may not be surprising that you can run this low-voltage, low-current cable in hazardous locations (as permitted in the applicable Chapter 5 Articles). You can also use it for direct burial applications, where it's identifed for that use [727.4]. One place where you will find this cable in huge amounts is under raised floors in information technology rooms. Especially if such rooms serve the control rooms of paper mills, refineries, and other measurement-intensive operations.
- Type ITC Cable is, by definition, operating at 150V or less and 5A or less. Thus, you cannot use it for circuits operating over 150V or over 5A [727.5]. No surprise here. Generally, you can't install Type ITC cable with other cables, unless the governing Articles contain stated provisions for such an installation. By default, that is, you can't mix Type ITC with other cables; you need explicit permission from an NEC Article that governs your particular installation [727.5].
- You absolutely cannot install Type ITC cable with power, lighting, Class 1 circuits that are non-power limited circuits (also off limits are those that are "not power limited) [727.5].
- A couple of exceptions apply to the two preceding points. One is where there's a metallic sheath or armor over the nonmetallic sheath of the Type ITC cable. Presumably, this will provide a Faraday cage. But it's best to maintain separation in the first place. Another exception is that you maintain separation by insulating barriers or other means, where the ITC cable is terminated within equipment or junction boxes.
- The construction and marking requirements are in 727.6 and 727.7. These are primarily for the manufacturer, but you also need to be able to know what ITC looks like and be able to read those markings to make sure the cable you're using is the ITC cable you intended to use.
- Some installers get fancy with their cable bends. While a nice, neat installation with uniform bends is desirable, don't use needle nose pliers to make sharp nineties in the cable. That will exceed the bend radius and damage the cable, something the NEC forbids [727.10]. The damage can make for a lot of "fun" trying to figure out why the operator's panel show the valve actuated but nothing's happening out in the plant. Use some type of arbor that will leave a gradual curve that doesn't exceed the bend radius. You might look up the actual number, or you could just apply common sense and the "feel" of the cable. If you're causing a sudden rise in the tension on the cable jacket while bending it with your fingers, you've hit the limit. Back off and make the bend over a larger radius next time. Don't use cable that you've already damaged by exceeding its bend radius.
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- Appendix D contains examples that every NEC user should study.
Try your NEC moxy:
- Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
- Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
- When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
- Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
- Take our Code Quizzes.
Remember other applicable codes, rules, standards, and references:
- OSHA's electrical worker safety rules.
- IEEE standards.
- NETA standards.
- NFPA standards.
- International Codes (if applicable to the installation).
- State Codes (if the state has them).
- Local ordinances and permit requirements.
- Local fire codes.
- Manufacturer requirements or guidelines.
- Customer security requirements.
- Industry standards.
- Your company's own internal standards, practices, and procedures.
- Engineering drawing notes.
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