High Ampacity Conductors for Large Motors

Leo1

Member
Location
Los Alamos, NM
Is there any NEC approved high capacity cabling for wiring 600hp, 720AMP (nameplate) motors? Is diesel locomotive cable ( RHH, RHW-2) the highest capacity that can be used? Even with this type cable is would still take 720 x 1.25 = 900AMPs of cable at 75 degrees C because the 90 degree C is only for de-rating.
 

Smart $

Esteemed Member
Location
Ohio
Even if you use high ampacity cable/conductor, you're stuck with the allowable ampacity of Table 310.15(B)(16), 75?C column as the minimum size.
 

Smart $

Esteemed Member
Location
Ohio
Even if you use high ampacity cable/conductor, you're stuck with the allowable ampacity of Table 310.15(B)(16), 75?C column as the minimum size.
However, there is a method of transitioning after the OCPD enclosure (and before load end, if also 75? rated). Let me know if interested...
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is there any NEC approved high capacity cabling for wiring 600hp, 720AMP (nameplate) motors? Is diesel locomotive cable ( RHH, RHW-2) the highest capacity that can be used? Even with this type cable is would still take 720 x 1.25 = 900AMPs of cable at 75 degrees C because the 90 degree C is only for de-rating.
It does not matter what kind of conductor you use. You still need 900A of ampacity. In most cases you cannot exceed the 75 deg C column in the chart.

1000 kcm is the largest wire I have even heard of. I doubt that even it is sufficient for 900A.

I think you will need to run smaller conductors in parallel. maybe two sets of 2X 250 kcm in 2 conduits.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
DLO does not have a higher ampacity rating than any standard building wire. Well it may be a bit higher because of the non-standard sizes, but anytime I use it, I use the T310.15(B)(16) ampacities for the next smaller standard size conductor.

The confusion comes from the way the manufacturer's of DLO tell you the ampacity of that type of cable. They almost always give the the 90?C ampacity in free air. Not an ampacity that can be used in this application.
 

Cow

Senior Member
Location
Eastern Oregon
Can you use 3-350mcm THHN per phase?

We've done 500HP 480v motors and it took 2-500mcm THHN per phase. How many and what size conduit entries into the motors j-box? That'll usually dictate what your options are.
 

Smart $

Esteemed Member
Location
Ohio
... How many and what size conduit entries into the motors j-box? That'll usually dictate what your options are.
Not always. Many are removable, and I've seen termination boxes replaced with larger ones.
 

kwired

Electron manager
Location
NE Nebraska
If you find higher ampacity conductors you are still limited by termination temperature ratings. And for 600 volt and less that is almost always going to be limited to 75C.
 
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