1. Junior Member
Join Date
Aug 2013
Location
New Jersey/Pa
Posts
9

## De-rating conductors

I know that the 90 deg C column can be used for calculating adjustment factors when 4 or more current carrying conductors are used in a conduit. But where is it specifically noted in the code. Chapter and verse.
Thank you

2. Look at 110.14(C).

3. Originally Posted by infinity
Look at 110.14(C).
That's the right spot. But you might consider waiting until you are off work and have a beer in your hands, before trying to figure out exactly what that article is telling you.

4. Senior Member
Join Date
Dec 2008
Posts
535
The article 114(C) (C) Temperature Limitations.it is a little confusing:
The temperature rating associated with the ampacity of a conductor shall be selected
(C) Temperature Limitations. The temperature rating associated
with the ampacity of a conductor shall be selected
and coordinated so as not to exceed the lowest temperature
rating of any connected termination, conductor, or device.
Conductors with temperature ratings higher than specified
for terminations shall be permitted to be used for ampacity
310.15 Ampacities for Conductors Rated 0–2000 Volts (B) Tables:
The temperature correction and adjustment factors shall
be permitted to be applied to the ampacity for the temperature
rating of the conductor, if the corrected and adjusted
ampacity does not exceed the ampacity for the temperature
rating of the termination in accordance with the provisions
of 110.14(C).
For instance let's take 1/0 copper conductor 90oC insulated
From Table 310.15(B)(16) I=170 A for 3 conductor per position
Now let's take 6 conductors from Table 310.15(B)(3)(a)
I=170*.8=136 A
From Table 310.15(B)(16) I=150 A for 75oC
That means since 136<150 A it is permitted.

5. Originally Posted by Julius Right
For instance let's take 1/0 copper conductor 90oC insulated
From Table 310.15(B)(16) I=170 A for 3 conductor per position
Now let's take 6 conductors from Table 310.15(B)(3)(a)
I=170*.8=136 A
From Table 310.15(B)(16) I=150 A for 75oC
That means since 136<150 A it is permitted.
Since your example has 6 CCC's you're derating will be 80% as you stated. However after the calculation those conductors are only 136 amp conductors and that is their maximum ampacity. Depending on the particulars you may be able to use a 150 amp OCPD with the 136 amp conductors via the next size up rule.