392.80[c] indicates where multi-conductor cable si sinstalled in tray with a min. spacing of one cable diameter the ampacity is based on "free air" rating in accordance with 310.15[c]? What is considered multi-conductor cable? If the cable assembly is an IAC [interlocked armored cable] type can you still apply this rating when it has an overall armor jacket and a pvc type jacket over the IAC?
Cable Tray Ampacity
- Thread starter Mike01
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Julius Right
Senior Member
- Occupation
- Electrical Engineer Power Station Physical Design Retired
IMO if the cable is declare AC cable as per art.320 then according 320.80 Ampacity. (B) Cable Tray: ?The ampacity of Type AC cable installed in cable tray shall be determined in accordance with 392.80(A).?
That means art.392.80 Ampacity of Conductors.
(A) Ampacity of Cables, Rated 2000 Volts or Less, in
Cable Trays.(c) will be suitable for this cable too.
That means art.392.80 Ampacity of Conductors.
(A) Ampacity of Cables, Rated 2000 Volts or Less, in
Cable Trays.(c) will be suitable for this cable too.
Mostafa Noah
Member
- Location
- Cairo, Egypt
My understanding is that the Armored cable will be treated as indicated in 392.80 [c], as long as the multicore cable has three conductor per cable [three live], not four conductors per cable [three live + neutral].
As noted, (c) is applicable to any 2 or 3 conductor cable permitted to be run in cable tray. The thing about being able to use free air ampacity for cables is that it often ends up moot because we are typically limited to the 75?C column allowable ampacity of Table 310.15(B)(16) in coordinating size and ampacity to the terminal temperature limitation of 110.14(C).
One way to increase this limitation is to apply a terminal temperature transition, installed at some distance from the regular terminal enclosure.
One way to increase this limitation is to apply a terminal temperature transition, installed at some distance from the regular terminal enclosure.
392.80[a][1][c]
392.80[a][1][c]
This refers to 310.15[c] with an information note to annex b Table B.310.15[2][3], when you reference this table this indicates that a 500kCMIL multi conductor cable at 75 degrees is rated for 416A. With a 3/C-MC type cable in cable tray with one diameter spacing this table would allow you to use 416A ampacity. My understanding was that feeders using IAC [interlocked armored cable] or MC [metal clad] type constuction were restricted to table 310.15[16]as the title reads "not more than three current carrying conductors in raceway, cable or earth". I always understood "cable" to include type IAC or MC construciton, as the increased ampacity has to do with the ability for heat dissipation and with the armored cable [IAC or MC] it was treated like a "cable" and subject to thoes ampacities listed in 310.15[16], when you refer to the manufacturers literature it list the ampacity as indicated in 310.15[16] for this type of cable too?
392.80[a][1][c]
This refers to 310.15[c] with an information note to annex b Table B.310.15[2][3], when you reference this table this indicates that a 500kCMIL multi conductor cable at 75 degrees is rated for 416A. With a 3/C-MC type cable in cable tray with one diameter spacing this table would allow you to use 416A ampacity. My understanding was that feeders using IAC [interlocked armored cable] or MC [metal clad] type constuction were restricted to table 310.15[16]as the title reads "not more than three current carrying conductors in raceway, cable or earth". I always understood "cable" to include type IAC or MC construciton, as the increased ampacity has to do with the ability for heat dissipation and with the armored cable [IAC or MC] it was treated like a "cable" and subject to thoes ampacities listed in 310.15[16], when you refer to the manufacturers literature it list the ampacity as indicated in 310.15[16] for this type of cable too?
Hameedulla-Ekhlas
Senior Member
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- AFG
Good Explanation.
1) Annex B tables are for information only and not used for Code compliance.
2) Read and understand section 310.15(B). Do not go directly to Table 310.15(B)(16) and rely solely on the information gleaned from its title. Also note specific conditions of 310.15(B)(3)(a), most notably for your scenario, (1), (4), and (5) thereunder.
3) If the cable exits the cable tray before it is terminated, the conditions change to those appropriate and you could very well have to determine ampacity for those sections using Table 310.15(B)(16).
Julius Right
Senior Member
- Occupation
- Electrical Engineer Power Station Physical Design Retired
IMO NEC states the same ampacity for armored cable and non-armored.The manufacturer indicates the NEC ampacity. For instance: in one of Teck 90 Armoured Power [TEXCAN] manufacturer catalogue the ampacity indicated fit NEC Table 310.15(B)(17) Allowable Ampacities of Single-Insulated Conductors for non-armored cables[90oC insulation]and Table 310.15(B)(16) for three-conductor cables [non-shielded].
See:
http://www.texcan.com/documents/Texcan Teck 1KV.pdf
Also, for shielded medium voltage armored cable the ampacity shown in catalogue fit Table 310.60(C)(71).See:
http://www.texcan.com/documents/Texcan Teck Medium Voltage Shielded.pdf
See:
http://www.texcan.com/documents/Texcan Teck 1KV.pdf
Also, for shielded medium voltage armored cable the ampacity shown in catalogue fit Table 310.60(C)(71).See:
http://www.texcan.com/documents/Texcan Teck Medium Voltage Shielded.pdf
Some do... but I have witnessed some that don't... and seldom do they cover all potential conditions of use. That said, there are only a few situations where a manufacturers published ampacity value is even permitted to be used in lieu of NEC values if theirs differs.
Confusing....
Confusing....
If the Annex B tables are for information only and not used for Code compliance why are they published in the code? 390.80[A][1][c] references back to 310.15[C] Engineering Supervision, reading through Article 310 my understanding is that the ampacity for these cables [IAC / MC] installed in tray with one cable spacing must be calculated and there is no ampacity table for this type of cable.
Confusing....
If the Annex B tables are for information only and not used for Code compliance why are they published in the code? 390.80[A][1][c] references back to 310.15[C] Engineering Supervision, reading through Article 310 my understanding is that the ampacity for these cables [IAC / MC] installed in tray with one cable spacing must be calculated and there is no ampacity table for this type of cable.
MasterTheNEC
CEO and President of Electrical Code Academy, Inc.
- Location
- McKinney, Texas
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- CEO
The installation of MC Cable per Section 330.10(B)(1) and the referenced sections. In terms of ampacity Section 330.80(A) refers you to 392.80. The most relevant application regarding ampacity for the example given is 392.80(A)(1) where it references Table 310.15(B)(16) and (B)(18). The reference you are speaking of, Section 310.15C is providing the ability to use an engineering supervision for an ampacity other than the tables referenced. This would be based on the Neher-McGrath method under the guidance of an electrical engineer and hopefully using a software and not by hand.
As to the Annex B being information only and why it is published in the code, to give guidance to the engineers doing the calculations. The reference to Annex B being for informational purposes only is stated right at the beginning of Annex B. It says " this informative annex is not a part of the requirements of this NFPA document but is included for informational purposes only."
Julius Right
Senior Member
- Occupation
- Electrical Engineer Power Station Physical Design Retired
I agree with you Mike: ?310.15[16] as the title reads "not more than three current carrying conductors in raceway, cable or earth.? However it is permissible to use the adjustment factors:
392.80 Ampacity of Conductors.(A) Ampacity of Cables, Rated 2000 Volts or Less, in Cable Trays.(1) Multiconductor Cables.
(a) The adjustment factors of 310.15(B)(3)(a) shall apply only to multiconductor cables with more than three current-carrying conductors. Adjustment factors shall be limited to the number of current-carrying conductors in the cable and not to the number of conductors in the cable tray.
Annex B indicates at IEEE 835/1994 for additional information. Here one can found an actual application-more detailed-of Neher and McGrath method.
392.80 Ampacity of Conductors.(A) Ampacity of Cables, Rated 2000 Volts or Less, in Cable Trays.(1) Multiconductor Cables.
(a) The adjustment factors of 310.15(B)(3)(a) shall apply only to multiconductor cables with more than three current-carrying conductors. Adjustment factors shall be limited to the number of current-carrying conductors in the cable and not to the number of conductors in the cable tray.
Annex B indicates at IEEE 835/1994 for additional information. Here one can found an actual application-more detailed-of Neher and McGrath method.
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