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How many current carring conductors?

3K views 24 replies 9 participants last post by  Cletis 
#1 ·
Question: You are wiring a bathroom. You are using EMT coming from a 200 amp, 3 phase, 120/208 wye panel board. One conduit will supply five hand dryers that operate at 13 amps, 120 volts. The breakers are 20 amps and are arranged in the panel so the least amount of wire is used. What would be the most current carrying conductors be in the pipe?
A: 5 B: 6 C: 7 D: 10

I need your assistance!
 
#5 ·
Question: You are wiring a bathroom. You are using EMT coming from a 200 amp, 3 phase, 120/208 wye panel board. One conduit will supply five hand dryers that operate at 13 amps, 120 volts. The breakers are 20 amps and are arranged in the panel so the least amount of wire is used. What would be the most current carrying conductors be in the pipe?
A: 5 B: 6 C: 7 D: 10

I need your assistance!
The question is in conflict with itself. You are asked to use the least amount of wire, but are asked what is the most CCCs.

6 or 10 are your options.
 
#12 ·
First off let me apologize for calling you Cletis, I need to be more careful when not wearing my glasses. :laughing: I will now try to make up for that.

OK, here is how I get there.

If you need to run 5 circuits using two MWBCs (multiwire branch circuits) from a 208Y/120 system this is how I would look at it.

MWBC #1

A

B

C

N

In this circuit A,B and C are current carrying conductors but N is not because it only carries the imbalance of the others. So we have 3 CCCs (Current Carrying Conductors)

2008 NEC references
310.15(B)(4)

(a)
A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit
shall not be required to be counted when applying the provisions
of 310.15(B)(2)(a).
MWBC #2

A

B

N

In this case A, B, and N are all current carrying conductors because the neutral carries more than the imbalance of the other conductors. So again we have 3 CCCs.

310.15(B)(4)

(b)
In a 3-wire circuit consisting of two phase conductors
and the neutral conductor of a 4-wire, 3-phase, wye connected
system, a common conductor carries approximately
the same current as the line-to-neutral load currents
of the other conductors and shall be counted when applying
the provisions of 310.15(B)(2)(a).
The answer is 6.
 
#17 ·
ok

Question: You are wiring a bathroom. You are using EMT coming from a 200 amp, 3 phase, 120/208 wye panel board. One conduit will supply five hand dryers that operate at 13 amps, 120 volts. The breakers are 20 amps and are arranged in the panel so the least amount of wire is used. What would be the most current carrying conductors be in the pipe?
A: 5 B: 6 C: 7 D: 10

I need your assistance!
5 hand dryer at 13 amp/120V to me means ALL 5 equal 13 amps / 120V

2.6 amps each dryer so them all on a 20 :eek:
 
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