/images/NEC_button.jpg/images/southwire_100x70.jpg2002 NEC Open Wiring Changes Ease Distance Limitations - March/April 20022002NECOpenWiringChangesEaseDistanceLimitationsMarandApril2002.htmHave you ever had problems bringing wiring from a cable tray system down to your process equipment? Check out the changes in the use of Type TC cables in the 2002 National Electrical Code (NEC).
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2002 NEC Open Wiring Changes Ease Distance Limitations - March/April 2002

Have you ever had problems bringing wiring from a cable tray system down to your process equipment? Check out the changes in the use of Type TC cables in the 2002 National Electrical Code (NEC).

"Cable trays are typically mounted up in the ceiling of a plant," says Dave Mercier, technical director of Southwire's Electrical Division. "And there may be obstacles to installing the tray system all the way down to equipment located on the plant floor. The NEC makes allowance for the transition, but what's allowed has changed in 2002."

Unlimited distance - and more support In the 1999 NEC, Section 340-4 (6) let you run tray cable as open wiring from the tray system to the equipment, provided you "supported and secured" the cable every 6 feet (1.83 m). The catch was that you could only do that for a maximum of 50 feet. In some installations, the 50-foot limit was a real hindrance.

In the 2002 NEC, the appropriate article is Section 336.10 (6). The new wording removes the 50-foot distance limitation - but it also adds a new stipulation. Now you have to "continuously support and protect" the cable against physical damage, using "struts, angles or channels."

Here's the new NEC wording 336.10 (6) In industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation, and where the cable is continuously supported and protected against physical damage using mechanical protection, such as struts, angles, or channel, Type TC tray cable that complies with the crush and impact requirements of Type MC cable and is identified for such use shall be permitted between a cable tray and the utilization equipment or device. The cable shall be secured at intervals not exceeding 1.8 m (6 ft). Equipment grounding for the utilization equipment shall be provided by an equipment-grounding conductor within the cable.

Know these five key points

Here are the key factors in the new section:

  • Allowed in industrial establishments where only qualified persons service the installation.
  • Cable must be continuously protected and supported by a physical structure.
  • Cable must meet Type MC crush and impact requirements.
  • You still have to secure it every 6 feet (1.83 m).
  • And, there's no distance limitation.

"The support structure adds some cost to the system," Mercier comments. "But it does let you go longer distances, which is a trade-off many people asked for. And if you think the requirements could be improved, contact the NFPA at www.necdirect.org and put in a proposal to change it. That's exactly how the code evolves."