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
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
If I do the math and de-rate with 7-9 ccc, I would use 70%( table 310.15 B 3). So 20 amps x .70= 14. So why not 9? I know the correct answer is 6, but I do not understand how to get there. Are we using 20 amps as a start to de-rate?
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).
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).
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
They draw and blow. Any blowing pressure out must have an equal and opposite sucking pressure.
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