table c10 in the nec

[kimrichi]

if i have 120/208 three phase system and if service conductors amp is 750 andit is parallel in 2 raceways when looking to find right size 40 pvc raceway should not be size(2 and half)to accommodate 4 conducter(3 HOT AND 1 NEUTRAL)?

 

[jumper]

AL or CU, what insulation? 2 sets 500mcm CU or 700 AL? If AL, 3 350mcm might be easier.

 

[Dennis Alwon]

I would not use annex C as that is for informational purpose and has a few errors in it. Use Chapter 9 Tables 4 and 5.

 

[jumper]

I would not use annex C as that is for informational purpose and has a few errors in it. Use Chapter 9 Tables 4 and 5.

But, I is lazy.

 

[Dennis Alwon]

But, I is lazy.

U iz is u... I seriously have found some major contradictions. In one case Annex C allowed 9 wires and the other method allowed 6.

 

[jumper]

U iz is u... I seriously have found some major contradictions. In one case Annex C allowed 9 wires and the other method allowed 6.

Wow. I heard it was screwed up, but that is bad. I remember when I came here that i was told I should drop Annex C, have not used it since, besides most test questions are mixed sizes so Annex C is no good anyways. They do it on purpose so you have to use Chap 9.

 

[kimrichi]

AL or CU, what insulation? 2 sets 500mcm CU or 700 AL? If AL, 3 350mcm might be easier.

it is THWN copper my question is the number of conductor should be 4 but in mike holt book(nec exam preparation 2008 edition page 294)he counts only 3 wires why?

 

[Dennis Alwon]

Unless the load being served is high in electronics and fluorescent lighting then there is probably a good chance the neutral is not counted-- but that is for ampacity derating not conduit fill. Look at 310.15(B)(4) 2008 Nec

 

[jumper]

Unless the load being served is high in electronics and fluorescent lighting then there is probably a good chance the neutral is not counted-- but that is for ampacity derating not conduit fill. Look at 310.15(B)(4) 2008 Nec

And it is somewhat rare that an upsized neutral is used for a feeder or service, or that the neutral is counted as CCC, mostly branch circuits in my experience.

 

[jumper]

And it is somewhat rare that an upsized neutral is used for a feeder or service, or that the neutral is counted as CCC, mostly branch circuits in my experience.

Before anyone nails me I am not talking about 1P 3w panels or circuits off 3P.

 

[jumper]

Infinity/Rob wrote this and I keep it bookmarked:

Here's some examples of when to count the neutral as a CCC:

208Y/120 volt system-different circuit types:

A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.

120/240 volt system-different circuit types:

D)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's

Notes:
D)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E)- In this circuit the neutral will only carry the imbalance between the two ungrounded condcutors so the neutral is not counted as a CCC.