Do I have to Derate

[copper chopper]

Now that most of us dont like to use 2 or 3 pole breakers on a networked branch circuits, we now use a neutral for every hot on the branch circuit. This allows us to use single pole breakers.I am talking about a typical 120/208 volt 3 phase panel.What my question is--what we want to know is this say your pulling homeruns back to the panel and typicaly we use 3/4 pipe for this.Well before we would only pull 9 wires,6 hots and 2 neutrals and 1 ground.Any more and we would have to derate to 50%.Well now we are pulling 6 hots and 6 neutrals,1 ground.In 310.15b4 page70-147 in the 2008 code.doesnt this state that the neutral conductor only is counted as a current carrying conductor when paired with more than 1 hot conductor.If we are correct on this then we use chapter 9 table c.1 page 70-705 that tells us that we can fit 16 wires of #12 awg in a 3/4 pipe.Thus we should be able to put 8 hots and 8 neutrals and 1 ground in those 3/4 emt pipes and be legal...IF NOT PLEASE GIVE ARTICLES ON WHY.....

 

[infinity]

Well before we would only pull 9 wires,6 hots and 2 neutrals and 1 ground.Any more and we would have to derate to 50%

This would likely require a derating of 70%, so you're correct.

70-705 that tells us that we can fit 16 wires of #12 awg in a 3/4 pipe.Thus we should be able to put 8 hots and 8 neutrals and 1 ground in those 3/4 emt pipes and be legal.

Ah, no. 8+8+1= 17 not 16. Also that would be 16 CCC's so you would need to derate to 50%.

 

[George Stolz]

In 310.15b4...in the 2008 code doesnt this state that the neutral conductor only is counted as a current carrying conductor when paired with more than 1 hot conductor.

Well, you're a little backwards there. A grounded conductor is not a neutral conductor unless a pair of ungrounded conductors are using it to return their unbalanced current.

Your situation is an ungrounded conductor generating heat paired with a grounded conductor carrying the same current in amps, and therefore generating the same heat.

The grounded conductors in your example are all current carrying conductors subject to derating.

 

[copper chopper]

Thanks infinity youIare correct i just wrote my example wrong sorry,,, what i really need to know is that when we use a neutral for every hot conductor, not using any networks, do we have to derate, because the way its worded in those articles we think not..... are we right or wrong...



as for goerge stolz you Obviously have not read those articles your answer does not help at all....

 

[jumper]

Thanks infinity youIare correct i just wrote my example wrong sorry,,, what i really need to know is that when we use a neutral for every hot conductor, not using any networks, do we have to derate, because the way its worded in those articles we think not..... are we right or wrong...

A two wire 120v circuit does not have a neutral. It has an ungrounded conductor and a grounded conductor. The grounded conductor is a current carrying conductor and is counted for derating purposes.

as for goerge stolz you Obviously have not read those articles your answer does not help at all....

George spelled it out pretty clearly.

 

[Volta]

Hey Chopper, welcome to the forum. But George has put it well here.

Well, you're a little backwards there. A grounded conductor is not a neutral conductor unless a pair of ungrounded conductors are using it to return their unbalanced current.

Your situation is an ungrounded conductor generating heat paired with a grounded conductor carrying the same current in amps, and therefore generating the same heat.

The grounded conductors in your example are all current carrying conductors subject to derating.

...
George spelled it out pretty clearly.

Yup, truly well said.

 

[jumper]

Okay chopper,

Let me ask you a question.

Can I put 3 120v networks/full boats (9 hots) with one shared grounded conductor per trio

(3 neutrals) consisting of #12 THHN conductors on 20amp breakers? 208Y/120 system voltage.

Why or why not?

 

[infinity]

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.

 

[jumper]

Nice job Rob. I just copied your post and saved it in a word doc for reference.:thumbsup:

 

[infinity]

Nice job Rob. I just copied your post and saved it in a word doc for reference.:thumbsup:

Funny thing is that I was 3/4 of the way through it and the power went off for a few seconds so I had to start all over.

One other note, I used the term neutral for all circuits in the examples. In the 2011 NEC they have defined a neutral conductor to be the conductor connect to the neutral point of the system. Sort of changes the old IEEE definition that you seemed to reference in post #5.

 

[jumper]

Funny thing is that I was 3/4 of the way through it and the power went off for a few seconds so I had to start all over.

One other note, I used the term neutral for all circuits in the examples. In the 2011 NEC they have defined a neutral conductor to be the conductor connect to the neutral point of the system. Sort of changes the old IEEE definition that you seemed to reference in post #5.

Good catch. Thanks.

 

[George Stolz]

The OP is correct, I did not apply Charlie's rule in reading 310.15(B)(5)(a). As it stands, I think the code language incorrectly allows this unsafe installation.

 

[jumper]

The OP is correct, I did not apply Charlie's rule in reading 310.15(B)(5)(a). As it stands, I think the code language incorrectly allows this unsafe installation.

You lost me George. What are you saying? His pipe is overfilled.

 

[copper chopper]

alright

alright

but answer me this, How do i know on a 120 volt circuit when does a neutral conductor carry only unbalanced load ?

 

[infinity]

but answer me this, How do i know on a 120 volt circuit when does a neutral conductor carry only unbalanced load ?

Did you look at the different circuit scenarios in post #8? Do you have a specific circuit in mind? (i.e.- 2, 3 or 4 wire)

 

[david luchini]

The OP is correct, I did not apply Charlie's rule in reading 310.15(B)(5)(a). As it stands, I think the code language incorrectly allows this unsafe installation.

George, you had it right the first time. The OP is misreading 310.15(B)(5)(a). That section says a neutral conductor that carries only the unbalanced current from other conductors (note: plural conductors) of the same circuit shall not be required to be counted...

He switched his two multi-wire branch circuits (each with 3 hots and 1 neutral) to six individual branch circuits (each with 1 hot and 1 neutral.)

310.15(B)(5)(a) cannot apply to the individual branch circuits, as there are not multiple "other conductors" of the same circuit, and there is no unbalanced current on the circuit. The hot and neutral obviously carry the same current.

but answer me this, How do i know on a 120 volt circuit when does a neutral conductor carry only unbalanced load ?

For the multiwire branch circuit (3 hots and 1 neutral) that you started with, the neutral would carry only the unbalanced load per 310.15(B)(5)(a). This would also apply to a mwbc (2 hots and 1 neutral) on a single phase, 3 wire system.

310.15(B)(5)(b) tells you that for a 3 wire MWBC (2 hots and a neutral) on a 3 phase, 4 wire system, the neutral will carry current, so it must be counted as a ccc.

310.15(B)(5)(c) tells you that for a 4 wire mwbc (3 hots and 1 neutral) where the majority of the loads are non-linear, the neutral must be counted as a ccc.

When you switched your 2 mwbc's to 6 individual branch circuits, you changed the quantity of current carrying conductors from 6 to 12. None of the provisions in 310.15(B) apply to your neutrals on the individual circuits.

 

[copper chopper]

thanks for all the info

thanks for all the info

SO IS 7 HOTS AND 7 WHITES OR NEUTRALS LEGAL WE DONT HAVE TO DERATE IN THIS CASE?

 

[Dennis Alwon]

SO IS 7 HOTS AND 7 WHITES OR NEUTRALS LEGAL WE DONT HAVE TO DERATE IN THIS CASE?

If you have 7 hots and 7 neutrals (they are really grounded conductors) then you have 14 current carrying conductors.

 

[ActionDave]

You have fourteen current carrying conductors. You have to derate by fifty percent.

 

[jumper]

SO IS 7 HOTS AND 7 WHITES OR NEUTRALS LEGAL WE DONT HAVE TO DERATE IN THIS CASE?

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