Conductors In A Raceway

[globe trekker]

I have a retired individual installing some lighting & circulating

(ceiling type) fans in an outdoor type pole barn. He is wanting

to install 6 - #12 conductors, THHW, in 1/2" sized EMT conduit

and have only one shared neutral for 2 of the lighting circuits.

2 questions have arisen regarding this installation.

QUESTION # 1: In looking at Tabel 1, in the 2008 NEC,

anything over 2 conductors is limited to 40% of the conductor

fill amount, which then goes to Table C.2. Table C.2 limits the

number of #12 THHW conductors inside a 1/2" EMT raceway to

3. Is this correct?



QUESTION # 2: In this pole barn project, there are 3 separate

circuits for the lighting and 2 separate circuits for the circulating

fans. The individual is wanting to install 6 - #12 conductors

inside the 1/2" EMT and share the neutral for the 2 separate

circuits. All of the proposed new circuits will have individual

OCPD's (breakers) inside the elec. panel.

Can the neutral be shared for intended, separate circuits?

If you can, please cite the applicable articles or code

sections, so that I can relay this information.

Thanks ya'll!



.

 

[Dennis]

I have a retired individual installing some lighting & circulating(ceiling type) fans in an outdoor type pole barn. He is wanting

to install 6 - #12 conductors, THHW, in 1/2" sized EMT conduit

and have only one shared neutral for 2 of the lighting circuits.

2 questions have arisen regarding this installation.

QUESTION # 1: In looking at Tabel 1, in the 2008 NEC,

anything over 2 conductors is limited to 40% of the conductor

fill amount, which then goes to Table C.2. Table C.2 limits the

number of #12 THHW conductors inside a 1/2" EMT raceway to

3. Is this correct?



QUESTION # 2: In this pole barn project, there are 3 separate

circuits for the lighting and 2 separate circuits for the circulating

fans. The individual is wanting to install 6 - #12 conductors

inside the 1/2" EMT and share the neutral for the 2 separate

circuits. All of the proposed new circuits will have individual

OCPD's (breakers) inside the elec. panel.

Can the neutral be shared for intended, separate circuits?

If you can, please cite the applicable articles or code

sections, so that I can relay this information.

Thanks ya'll!

No, you can have 9 #12 in emt according to table C. Table C1

The neutral can share 2 circuits in a single phase panel and they must be on opposite phases and tied with a breaker tie or use a DP breaker.

I am a bit confused on the 6 circuits. I think you mean 2 circuits from the panel and the other wires are switch legs. Yes?

 

[Dennis]

Table 310.15(B)(2)(a) requires that we derate for current carrying conductors when we get over 3 wires in a conduit. Are you sure the conductors are THHW and not THWN?

If it is THHW then in wet location it is rated 75C otherwise it is rated 90C. Sounds like this is not wet so assuming 90C the wire is rated 30amps. Since we must derate 80% for 4-6 conductors then we have 80% X 30 + 24 amps so #12 is fine on a 20 amp cir.

The fill in Annex C is really not part of the NEC but is used for informational purposes. Normally you would use Chapter 9 and Calculate the size wire and the size of the conduit.

I think the mistake you made was taking 40% of the Number in Annex C-- Annex C has taken that into account.

 

[Dennis]

So I did the calculation from Chapter 9. Table 4 states the sq. in of 1/2" emt is .122 for over 2 wires (40%). #12 THHW is equal to .0181 from Chapter 9 Table 5. .122/.0181= 6.74 so 6 wires are allowed.

 

[Dennis]

Sorry for all the posts.. My first post is incorrect-- you can have 9 thhn/thwn conductors. THHW will only allow 4 according to the table C1 but that is not the table we use. The calc is correct above-- I hope.

 

[globe trekker]

Dennis,

Thanks for your input!

You are correct about the 2 separate circuits, and using switch legs

from the lighting fixtures.

I was told that the type of conductors to be used was THHW, #12,

with 6 being proposed to be installed in the 1/2" EMT.

The individual asking me was concerned about "backfeed" from the

other light fixtures off of the switched leg type connection, and the

actual number of conductors that can be installed in the 1/2" sized

EMT.

Your input and calculations are extremely helpful! MEGA thanks!

.

 

[Dennis]

You're welcome. The reason I asked about thhw is that is not a typical wire used, at least not around here. It is a bit thicker then thhn/thwn so most contractors prefer it to thhw.

This type of installation is done quite regularly. Now if you guys are under the 2011 NEC you would be required to have a conduit large enough to add the neutral to the switch should it be needed. In that case you will not be compliant as that would be the 7th wire. Using thhn/thwn it would not be an issue.

 

[globe trekker]

My AHJ is using the 2008 NEC, but the install will be going in to an area with no codes adopted.

Yep, absolutely "no codes of any type adopted!"

Thanks again for your input and the calculations.!

.

 

[globe trekker]

Dennis ( and others ),

I am still researching / clarifying this install for an individual. You mentioned ( above ),

that Table C.1 is not the Table to use, because that Table only shows / allows 4

conductors. In my copy of the "Ugly's Electrical Desk Reference", they show that

6 conductors ( of the THHW type ) are permitted to be installed in the ½" EMT conduit.

The calculations say 6 conductors allowed, the Table says only 4.

Which one is correct?

.

 

[Gregg Harris]

Dennis ( and others ),I am still researching / clarifying this install for an individual. You mentioned ( above ),

that Table C.1 is not the Table to use, because that Table only shows / allows 4

conductors. In my copy of the "Ugly's Electrical Desk Reference", they show that

6 conductors ( of the THHW type ) are permitted to be installed in the ½" EMT conduit.

The calculations say 6 conductors allowed, the Table says only 4.

Which one is correct?

.

The math provided by Dennis in post # 4 is correct according to NEC for fill of the EMT provided there will not be any ground wires added.

The Annex C1 can clearly be used because it exceeds the requirements and allows for for lead-way for a longer or tighter pull and manufacturing tolerance of the EMT.

 

[globe trekker]

Bringing this mostly dead horse back in for some more beating..

Gregg H.,

When adopting the NEC, if an AHJ does not specifically

adopt each Annex, it is my understanding that the information

in those Annexes cannot be used, even though they may be

accurate. Is this your (and others) experience in this case?

The Annex C tables DO provide a fount of information, but

we did not specifically adopt them in to our other adopted

codes & standards.

Ya'lls thoughts !

 

[BSSTG]

Greetings,

Beware of loading too many current carrying conductors without derating per 310.15(B)(3)(a)

BS

 

[Gregg Harris]

Bringing this mostly dead horse back in for some more beating..Gregg H.

When adopting the NEC, if an AHJ does not specifically

adopt each Annex, it is my understanding that the information

in those Annexes cannot be used, even though they may be

accurate. Is this your (and others) expereince in this case?

The Annex C tables DO provide a fount of information, but

we did not specifically adopt them in to our other adopted

codes & standards.

Ya'lls thoughts !

I would agree if they were not adopted, but in most cases I believe they exceed what is in the code and if used should work.

 

[mtlogcabin]

but the install will be going in to an area with no codes adopted.Yep, absolutely "no codes of any type adopted!"

We have areas in the state that are not regulated by codes and the local/state courts have consistantly allowed the code books to be used as a minimum "construction standard" that contractors should be following.

Of course only a small few ever see the inside of a courtroom.

 

[Dennis]

Dennis ( and others ),I am still researching / clarifying this install for an individual. You mentioned ( above ),

that Table C.1 is not the Table to use, because that Table only shows / allows 4

conductors. In my copy of the "Ugly's Electrical Desk Reference", they show that

6 conductors ( of the THHW type ) are permitted to be installed in the ½" EMT conduit.

The calculations say 6 conductors allowed, the Table says only 4.

Which one is correct?

.

Well I just spent about 10 hours looking and creating a spreadsheet to see what was going on in ANNEX C. I found a few calculation errors but specific to your question is that I found Annex C is labeled incorrectly.

Go to the Table C.1 and look on the left for TW. That section should be TW, THHW, THW, THW-2. The next 3 sections should be labeled RHH*, RHW*, RHW-2*-- YOU NEED TO DELETE THE THHW, THW AND THW-2 FROM THOSE SECTIONS.

 

[globe trekker]

Dennis,

Thanks for the update!

.