Question #3 June Q & A

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stwalkover

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Question 3 in the June Q & A says 9 current carrying condutors. Are we assuming 220 volts is being used? At 120 volts there are 5 current carrying condutors 3-12's + 2-12's is 5. 310.15 (B)(4). That is 80% and 24 amps.
 
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I have no idea what you are talking about. Please don?t assume that we all have whatever book you read, to get this question. You will have to pose a more complete question, and give more information about the situation, before I can help.
 
stwalkover,
I think this is the answer you are asking about.
Example: 20A Circuit. If we bundle three 12/2 and one 12/3 cable (nine current-carrying 12 THHN conductors), the ampacity for each conductor (30A at 90?C, Table 310.16) is adjusted by a 70 percent adjustment factor [Table 310.15(B)(2)(a)].
Adjusted Conductor Ampacity = 30A x 0.70
Adjusted Conductor Ampacity = 21A
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You said:
At 120 volts there are 5 current carrying condutors 3-12's + 2-12's is 5. 310.15 (B)(4). That is 80% and 24 amps.
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Actually both you and Mike are wrong. There are 8 current carrying conductors in this example. When you have 2 conductor cables you do not have a neutral, you have a grounded conductor and the grounded conductor in a 2 wire circuit is always a current carrying conductor. So the three two conductor cables have a total of 6 current carrying conductors. The neutral of a 3 wire circuit from a 120/240 volt single phase system is never required to be counted as a current carrying conductor so the 3 conductor cable has 2 current carrying conductor for a total of 8 in the bundle requiring a 70% derating.
Don

 
Or Mikes's right if the 12/3 is supplied by a 208Y/120 service or supplying a three phase load.

It seems we are still short on info.:smile:
 
Junes Q & A

Junes Q & A

Sorry! I did not mean to offend you with my Question and I was assuming that everyone had received Mikes e-mail. I was referring to Mikes Internet Connections and the NEC Code Questions Part 1 of 2 for June I recieve via email. I am new at Posting. Don I was using Trade language and 12/2 would be considered 1 black, 1 white (used as a Neutral) and 1 ground. The white would only be current carrying when marked a color other than white at that point. Another lesson in assumption for me.
 
Thanks for clarifying the source of your question. I do not subscribe to Mike?s email related to code questions.

As to whether a conductor is considered ?current carrying,? in the context of 310.15(B)(2)(a), that is not driven by the color of the wires. If a circuit has one ungrounded conductor and one grounded conductor, both conductors count as being ?current-carrying.? A 12/2 will count as two current-carrying conductors, as Don said earlier.
 
Don I was using Trade language and 12/2 would be considered 1 black, 1 white (used as a Neutral) and 1 ground. The white would only be current carrying when marked a color other than white at that point.
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The white will always be a current carrying conductor in the case of a 12/2 cable.
Don
 
stwalkover said:
I was using Trade language and 12/2 would be considered 1 black, 1 white (used as a Neutral) and 1 ground. The white would only be current carrying when marked a color other than white at that point. Another lesson in assumption for me.
Click to expand...

To go along with Don's post, see the illustration below.

not_a_neutral.JPG


Roger
 
macmikeman said:
If the three wire cable is for a three way switch- dead ended, then do we count all three wires or only two of them?
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Only two, there would never be current flowing on all three at the same time.

Roger
 
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