Minimum Number of Conductors?
- Thread starter wcv111
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Nearly true. Most often true. Well, actually, there is no rule that says that, but it is a consequence of a rule.
300.3(B) tells us that all conductors of a given circuit must be in the same raceway. Since you can?t build a circuit with a single conductor, then you wind up having to have at least two conductors in a raceway. There are rare exceptions, called ?iso-phase? runs, but I do mean ?rare.?
300.3(B) tells us that all conductors of a given circuit must be in the same raceway. Since you can?t build a circuit with a single conductor, then you wind up having to have at least two conductors in a raceway. There are rare exceptions, called ?iso-phase? runs, but I do mean ?rare.?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I guess one conductor can be in a raceway if it is an GEC.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I recall reading about a WWII era wiring system used in Europe where the conduit itself was used as the grounded _conductor_. Single ungrounded wire in the conduit, devices connected between that wire and the conduit. Hope they carefully tightened up the connector screws 
-Jon
-Jon
- Location
- New Jersey
- Occupation
- Journeyman Electrician
What if I had two PVC boxes with two 1/2" PVC raceways between the two boxes? Couldn't I put one conductor in one raceway and two in the other?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Man, I bet Bill V. from Ohio wishes he never asked his question. lol
Confused now???
Confused now???
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
i s'pose so, but if they were that large, I'd prefer a single 3/4" conduit.infinity said:
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
OK. Let's give him a simple and truthful answer to the question that he asked. That would be a novel thing for us.Dennis Alwon said:
The answer is "No." There is no NEC rule that explicitly states that a conduit is not permited to contain only one conductor.
tryinghard
Senior Member
- Location
- California
?Hysteresis? might play a role?
?Hysteresis? might play a role?
Notice 300-20 & (B)(1) along with FPN
From my limited understanding: due to AC & its cycles the electromagnetic field of a single conductor causes the molecules in metal to align & re-align. This aligning & re-aligning causes induced heating know as ?hysteresis heating?.
With this considered it is best practice to avoid single conductors in conduit, especially metal. I think parallel conductors in single conduits [a most common application] act as a single conductor, and hysteresis needs to be considered.
?Hysteresis? might play a role?
Notice 300-20 & (B)(1) along with FPN
From my limited understanding: due to AC & its cycles the electromagnetic field of a single conductor causes the molecules in metal to align & re-align. This aligning & re-aligning causes induced heating know as ?hysteresis heating?.
With this considered it is best practice to avoid single conductors in conduit, especially metal. I think parallel conductors in single conduits [a most common application] act as a single conductor, and hysteresis needs to be considered.
Tryinghard got one part that is in referenced in the code. I'll throw in part two for discussion, believe that it covers the requirements of a single conductor in a conduit, or raceway...
Chapter 9 Table 1, Percent ofcross section of conduit and Tubing for conductors -
1 conductor - 53 % fill
2 conductor - 31 % fill
over 2 is the normal 40% fill note.
Chapter 9 Table 1, Percent ofcross section of conduit and Tubing for conductors -
1 conductor - 53 % fill
2 conductor - 31 % fill
over 2 is the normal 40% fill note.
tryinghard
Senior Member
- Location
- California
Also notice 300-3 (B): ?All conductors of the same circuit?shall be contained within the same raceway?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
tryinghard said:
You need to read down a little further. 300.3(B)(3) Nonferrous wiring methods are allowed to be in separate raceways.
tryinghard
Senior Member
- Location
- California
infinity said:
It appears the intent of this section is to control or eliminate induced heat and for single conductors: "shall comply with the provisions of 300-20 (B)" which I listed in post #11 above. The rest of this section seems to be for cable but again it is to control or eliminate induced heat.
I think the most common situation with single conductors causing hysteresis or induced heat is with parallels. Parallels in individual conduits or raceways act as one conductor with cycles.
Other that parallels one should simply avoid installing individual conductors of a circuit in separate conduits or raceways, this practice most often cannot comply with NEC.
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