About adjustment factor of cable

L

Learner

Member
Location
Korea
Occupation
electric engineer
Thank you for reading my question.

I have question about terms and adjustment factor of cable.

1. 4c tc-type cable, the cores of cable is current-carrying conductors right?

2. If i use tray and tc-type 4c cable to power the electric equipment in plant, the system is 4wire 3phase wye circuit.
Following Table 310.15(C)(1) Adjustment Factors. Can i apply 80% factor to 4c cable ampacity?

3. If i'm wrong how can i use this table?

4. can you teach me how to calculate ampacity of cable by NEC?

5. raceway and cable tray is different right?
 
tom baker

tom baker

First Chief Moderator
Staff member
Location
Bremerton, Washington
Those questions are a bit bit beyond what we can do on this forum, esp question 4, but we can get you started
I would suggest you get a copy Mike Holts Understanding the NEC chapters 1-4
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Seconding what @tom baker says above, we can't teach you the totality of what you should learn from existing books. But when you have specific questions or misconceptions we can help clarify.

On the specific question of the 4 core cable, if all 4 cores are considered current carrying conductors then yes you would use the 80% factor.

However in the situation you describe (3 phase and neutral of a wye system) the neutral conductor usually doesn't count for the purpose of ampacity adjustment.

This doesn't mean that no current flows on the neutral, just that in a normal wye system the heat produced by the set of 4 conductors is no more than that expected from 3 conductors. In these situations the 80% factor doesn't apply.

There are uncommon situations where all 4 conductors heat, eg high harmonic loads, unbalanced neutral loading, etc. where the 80% factor would apply.
 
You must log in or register to reply here.
Top