Table 400.5(A)(2) vs. manufacturer spec

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JES2727

Senior Member
Location
NJ
According to Table 400.5(A)(2), 5 wire 2/0 type W cable has an ampacity of 237 at 90 degrees (three current carrying conductors). According to the manufacturer's spec the ampacity is 189 ( http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet200 ). They are applying the 80% adjustment according to Table 400.5(A)(3), so they are considering four conductors to be current carrying. I am looking at the 75 degree column, subheading F, and seeing 208 amps.
I'm fabricating a power cord for a 65kw portable generator with a 200 amp output breaker ( 3 phase, 120/208). I've asked for 2/0, the manufacturer says I need 3/0. I disagree.
Is the neutral to be considered current carrying in this application?
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
It depends on what you are supplying with this feeder.

If the majority of the load is non-linear yes it would be considered a current carrying conductor. See 310.15(B)(5)(c). 2011.


310.15(B)(3)(5) Neutral Conductor.

(a) A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit shall not be
required to be counted when applying the provisions of
310.15(B)(3)(a).

(b) In a 3-wire circuit consisting of two phase conductors
and the neutral conductor of a 4-wire, 3-phase, wye-connected
system, a common conductor carries approximately the same
current as the line-to-neutral load currents of the other conductors
and shall be counted when applying the provisions of
310.15(B)(3)(a).

(c) On a 4-wire, 3-phase wye circuit where the major
portion of the load consists of nonlinear loads, harmonic currents
are present in the neutral conductor; the neutral conductor
shall therefore be considered a current-carrying conductor.
Click to expand...
 
Smart $

Smart $

Esteemed Member
Location
Ohio
JES2727 said:
...According to the manufacturer's spec the ampacity is 189 ( http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet200 ). They are applying the 80% adjustment according to Table 400.5(A)(3), so they are considering four conductors to be current carrying. I am looking at the 75 degree column, subheading F, and seeing 208 amps...
Click to expand...
The CURRENT AMPS header in the linked pdf has an asterisk after it. The associated note at the end of the table says, "*Ampacities based on 90?C Conductor and 30?C Ambient temperature per table 400.5(B) of the 2011 National Eletrical Code?"...

AFAICT, there is no such table in the 2011 NEC...???
 
J

JES2727

Senior Member
Location
NJ
Smart $ said:
The CURRENT AMPS header in the linked pdf has an asterisk after it. The associated note at the end of the table says, "*Ampacities based on 90?C Conductor and 30?C Ambient temperature per table 400.5(B) of the 2011 National Eletrical Code?"...

AFAICT, there is no such table in the 2011 NEC...???
Click to expand...

It's 400.5(B) in the 2008 code.


The generator will serve a panel with three 3phase circuits. I'll stick with the 2/0.
 
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