2000A 277/480V Service Conductor Size - Derating??

Status
Not open for further replies.
M

Mike2006

Member
Location
Texas
I am feeding a 2000 Amp MDP that has a Main Breaker in a school. Will the conductors in each conduit (6 sets of 3 500 MCM Hots, 1 500 MCM Neutral and 1 Ground) have to be derated?
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Mike2006 said:
I am feeding a 2000 Amp MDP that has a Main Breaker in a school. Will the conductors in each conduit (6 sets of 3 500 MCM Hots, 1 500 MCM Neutral and 1 Ground) have to be derated?
Click to expand...
In most cases the neutral would not need to be counted as a current carrying conductor, so you would be OK (2 X 380=2280). Many times this is a judgment call depending on the types of load. If the decision is made that the neutral counts, then you would be a little shy (6 X 380 X .8=1824).
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I'm still not convinced that it would be more than 50% of the load. Factor in pumps, chillers, elevators, motors, fans, heaters, general purpose receptacles, etc., a data center, maybe. :)
 
Last edited:
A

Adnan Hasan

Member
Location
baghdad, Iraq
texie said:
In most cases the neutral would not need to be counted as a current carrying conductor, so you would be OK (2 X 380=2280). Many times this is a judgment call depending on the types of load. If the decision is made that the neutral counts, then you would be a little shy (6 X 380 X .8=1824).
Click to expand...
Dear texie.. I dont understand the followings: (2 X 380=2280) and (6 X 380 X .8=1824). Would you please explain to me? please refer to the code/section.. I just want to learn :huh:
why MCM but not kcmil?
the 380 is current Ampacity for 500 kcmil @ 75 dgree C. right?
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Adnan Hasan said:
Dear texie.. I dont understand the followings: (2 X 380=2280) and (6 X 380 X .8=1824). Would you please explain to me? please refer to the code/section.. I just want to learn :huh:
why MCM but not kcmil?
the 380 is current Ampacity for 500 kcmil @ 75 dgree C. right?
Click to expand...

Since he is not currently on-line, I would think that the 1st is simply a typo.. 6 x 380 is 2280 (he has 6 conductors) and the ,8 multiplier would be a factor IF the neutral was counted as a current-carrying conductor.
For most of us ole timers wire is still MCM.. the terminology kcmil takes a while to sink in :)
 
Last edited:
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
Adnan Hasan said:
Dear texie.. I dont understand the followings: (2 X 380=2280) and (6 X 380 X .8=1824). Would you please explain to me? please refer to the code/section.. I just want to learn :huh:
why MCM but not kcmil?
the 380 is current Ampacity for 500 kcmil @ 75 dgree C. right?
Click to expand...

Texie just had a typo, he meant 6 x 380= 2280.

MCM is just the old version of kcmil.

The .8 is for derating, if required, for 4 or more CCC.
Table 310.15(B)(3)(a) Adjustment Factors for More Than
Three Current-Carrying Conductors in a Raceway or Cable

Yes, 380 is the ampacity of 500 kcmil @ 75C.
 
A

Adnan Hasan

Member
Location
baghdad, Iraq
jumper said:
Texie just had a typo, he meant 6 x 380= 2280.

MCM is just the old version of kcmil.

The .8 is for derating, if required, for 4 or more CCC.
Table 310.15(B)(3)(a) Adjustment Factors for More Than
Three Current-Carrying Conductors in a Raceway or Cable

Yes, 380 is the ampacity of 500 kcmil @ 75C.
Click to expand...
many thanks..
 
Status
Not open for further replies.
Top