392.11.Ampacity of Cables Rated 2000 Volts or Less in Cable Trays. (B) Single Conductor Cables.
Single conductor cables can be installed in a cable tray cabled together (triplexed, quadruplexed, etc.) if desired. Where the cables are installed according to the requirements of Section 392.10, the ampacity requirements are shown in the following chart as per Section 392.11(B)(1), (2), (3), & (4):
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| Solid | Applicable | Amp. |
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Sec. | Cable | Unventilated | Ampacity | Table | Special |
No. | Sizes | Cable Tray | Tables | Values | Conditions |
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| Cover | (*) | By |
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| 600 kcmil | No Cover | 310.17 |
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(1) | and | Allowed | and | 0.75 |
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| Larger | (**) | 310.19 |
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| 600 kcmil |
| 310.17 |
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(1) | and | Yes | and | 0.70 |
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| Larger |
| 310.19 |
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| 1/0 AWG | No Cover | 310.17 |
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(2) | through | Allowed | and | 0.65 |
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| 500 kcmil | (**) | 310.19 |
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| 1/0 AWG |
| 310.17 |
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(2) | through | Yes | and | 0.60 |
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| 500 kcmil |
| 310.19 |
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| 1/0 AWG |
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| Maintained |
(3) | & Larger | No Cover | 310.17 | 1.00 | Spacing Of |
| In Single | Allowed | and |
| One Cable |
| Layer | (**) | 310.19 |
| Diameter |
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| Single |
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| Conductors |
| 310.20 |
| Spacing Of |
(4) | In Triangle | No Cover | [See NEC |
| 2.15 x One |
| Config. | Allowed | Section | 1.00 | Conductor |
| 1/0 AWG | (**) | 310.15(B)] |
| O.D. Between |
| and Larger |
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| Cables(***) |
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(*) The ambient ampacity correction factors must be used.
(**)At a specific position, where it is determined that the tray cables require mechanical protection, a single cable tray cover of six feet or less in length can be installed.
The wording of Section 392.11(B)(4) states that a spacing of
2.15times one conductor diameter is to be maintained between circuits. Two interpretations of this statement are possible. Interpretation #1. - The 2.15 times one conductor diameter is the distance between the centerlines of the circuits (the center lines of the conductor bundles). Interpretation #2. - The 2.15 times one conductor diameter is the free air distance between the adjacent cable bundles. The use of the word “circuit” is unfortunate as its presence promotes Interpretation #1. An installation based on Interpretation #1 is not desirable as a free air space equal to 2.15 times one conductor diameter between the cable bundles should be maintained to promote cable heat dissipation.
Cable Tray Manual
Spacing Between Conductors
(2.15 x O.D. of Conductor)
Technically Undesirable Installation
Interpretation #1
Spacing Between Conductors
(2.15 x O.D. of Conductor)
Technically Desirable Installation
Interpretation #2
392.12.Number of Type MV and Type MC Cables (2001 Volts or Over) in Cable Trays.
Sum the diameters of all the cables (Sd) to determine the minimum required cable tray width. Triplexing or quadruplexing the cables does not change the required cable tray width. Whether the cables are grouped or ungrouped, all installations must be in a single layer.
392.13.Ampacity of Type MV and Type MC Cables (2001 Volts or Over) in Cable Trays. (A) Multiconductor Cables (2001 Volts or Over).
Provision No. 1: Where cable trays are continuously covered for more than six feet (1.83 m) with solid unventilated covers, not more than 95% of the allowable ampacities of Tables 310.75 and 310.76 shall be permitted for multiconductor cables.
Cables installed in cable trays with solid unventilated covers must be derated. Where cable tray covers are to be used, it is best to use raised or ventilated covers so that the cables can operate in a lower ambient temperature.
Cooper B-Line, Inc
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