392.20 Cable and Conductor Installation.

Cable tray barriers can be used to separate conductors operating over 600 volts from other conductors in the same tray operating at 600 volts or less.
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Cable tray barriers can be used to separate conductors operating over 600 volts from other conductors in the same tray operating at 600 volts or less.

Code Change Summary: A clarification was made regarding separation of conductors in cable trays when conductors operate at different voltage levels.

In the 2011 NEC®, conductors in a cable tray “rated” over 600 volts would require separation from other conductors “rated” at 600 volts or less in the same cable tray. Even if all conductors in the cable tray “operate” at 600 volts or less, the separation requirements would be triggered because of the different voltage “rating” of the conductors.

Sometimes 1000 volt rated conductors are selected even if the operating voltage of the conductors is 480 volts. There is nothing prohibiting an electrical engineer from designing an electrical system above the minimum standards mentioned in the NEC®.

For example, in a facility where the maximum available voltage is 480 volts, it would be pointless to require separation in the cable tray between two sets of 480-volt conductors just because one set has conductor insulation rated at 600 volts and the other has 1000-volt rated insulation.

In the 2014 NEC®, the issue has been resolved by replacing the words “rated” with “operating at”.

Below is a preview of the NEC®.  See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).

2011 Code language:

392.20(A) Multiconductor Cables Rated 600 Volts or Less. Multiconductor cables rated 600 volts or less shall be permitted to be installed in the same cable tray.

392.20(B) Cables Rated Over 600 Volts. Cables rated over 600 volts and those rated 600 volts or less installed in the same cable tray shall comply with either of the following:

(1) The cables rated over 600 volts are Type MC.

(2) The cables rated over 600 volts are separated from the cables rated 600 volts or less by a solid fixed barrier of a material compatible with the cable tray.

2014 Code Language:

392.20(A) Multiconductor Cables Operating at 600 Volts or Less. Multiconductor cables operating at 600 volts or less shall be permitted to be installed in the same tray.

392.20(B) Cables Operating at Over 600 Volts. Cables operating at over 600 volts and those operating at 600 volts or less installed in the same cable tray shall comply with either of the following:

(1) The cables operating at over 600 volts are Type MC.

(2) The cables operating at over 600 volts are separated from the cables operating at 600 volts or less by a solid fixed barrier of a material compatible with the cable tray.

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392.20 Cable and Conductor Installation.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

In a building where the maximum voltage is 480 volts, which of the following is true for a cable tray containing conductors rated at 600 volts and other conductors rated at 2000 volts?

A: Separation is required between the 600 volt rated conductors and the 2000 volt rated conductors.
B: Cable trays are not permitted to contain conductors rated over 600 volts.
C: No separation is required between the 600 volt rated conductors and the 2000 volt rated conductors because all conductors operate at 600 volts or less.
D: The cable tray must have a label that says “WARNING-KEEP AWAY”.
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