Article 727 of the National Electrical Code (NEC) addresses instrument tray cable (ITC) and its permitted uses. In industrial locations, ITC cable is commonly used for instrumentation circuits in association with distributed control systems (DCSs). ITC cable is a perfect wiring method for these low-voltage, low-power installations. The typical DCS system will have I/O at a max of 24V. The I/O cards within the DCS system usually limits the power to the parameters set forth in Sec. 727.5.
The insulation level on ITC cable is rated for 300V, although the voltage level won’t be indicated on the cable jacket (Sec. 727.7). The voltage rating isn’t marked on the cable jacket because it could be confusing —some users might have a cable marked 300V and think it’s okay to apply 240V or 277V, which isn’t allowed.
There are several advantages to using ITC cable. Because the insulation rating is 300V, the outer diameter (O.D.) of the cable is much smaller than that of 600V rated cable. This becomes important, for instance, in cable tray fill and under raised floors of control rooms when crossing from the DCS cabinets to the marshalling cabinets.
Be careful when specifying ITC cable. ITC-ER (exposed run) cable must be used wherever the cable is exposed for any length. Using ITC cable without the “–ER” rating is a common issue right now in industrial facilities and probably will continue to be until all ITC cable is “–ER” rated — just like the transformation that occurred with 600V-rated tray cable (type TC) several years ago.
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