[RE-wrenches] NEC Art 310 Ampacity

Dave Click daveclick at fsec.ucf.edu
Thu Aug 6 08:48:01 PDT 2009


Here's a cable that may use B.310.1, which is probably overkill for most 
of our work:
http://www.amercable.com/doc/catalogs/VFDCables.pdf

MC cable requires you to use Table 310.16 for your 600V wires, with a 
few caveats (330.80)

That being said, not sure what "raceway in free air" means. Maybe 
they're trying to draw a distinction between that and underground ducts 
(e.g. Table B.310.5)

Here's the 330.80 section:
***
330.80 Ampacity.
The ampacity of Type MC cable shall be determined in accordance with 
310.15 or 310.60 for 14 AWG and larger conductors and in accordance with 
Table 402.5 for 18 AWG and 16 AWG conductors. The installation shall not 
exceed the temperature ratings of terminations and equipment.
(A) Type MC Cable Installed in Cable Tray. The ampacities for Type MC 
cable installed in cable tray shall be determined in accordance with 
392.11 and 392.13.
(B) Single Type MC Conductors Grouped Together. Where single Type MC 
conductors are grouped together in a triangular or square configuration 
and installed on a messenger or exposed with a maintained free airspace 
of not less than 2.15 times one conductor diameter (2.15 × O.D.) of the 
largest conductor contained within the configuration and adjacent 
conductor configurations or cables, the ampacity of the conductors shall 
not exceed the allowable ampacities in the following tables:
(1) 	Table 310.20 for conductors rated 0 through 2000 volts
(2) 	Table 310.67 and Table 310.68 for conductors rated over 2000 volts
***

-------- Original Message --------
Subject: [RE-wrenches] NEC Art 310 Ampacity
From: Peter Parrish <peter.parrish at calsolareng.com>
To: 'RE-wrenches' <re-wrenches at lists.re-wrenches.org>
Date: 2009/8/5 16:45

> When we do ampacity calculations, we always use Table 310.16 in Section
> 310.15 for wire in raceway (EMT, PVC, FMC, LNFC, LMFC), and MC cable. Of
> course we use Table 310.15(B)(2)(a) in a raceway or cable with more than
> three conductors.
> 
> A colleague asked me about the applicability of table B.310.1. It would seem
> to apply to 2-3 conductors within an overall covering (multi-conductor
> cable) in raceway in free air. Would MC apply? But what in the world is a
> "cable, in raceway, in free air"?  I'm usually pretty good in parsing this
> stuff, but this stumps me.
> 
>                                                      
> - Peter
> 
> Peter T. Parrish, President
> California Solar Engineering, Inc.
> 820 Cynthia Ave., Los Angeles, CA 90065
> CA Lic. 854779, NABCEP Cert. 031806-26
> peter.parrish at calsolareng.com  
> Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
> 
>  
> 
> 
> _______________________________________________
> List sponsored by Home Power magazine
> 
> List Address: RE-wrenches at lists.re-wrenches.org
> 
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
> 
> List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
> 
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
> 
> Check out participant bios:
> www.members.re-wrenches.org
> 
> 



More information about the RE-wrenches mailing list