I need to run a 20a/240v 4wire circuit. I have a lifetime supply of 12/2 on hand but would have to buy the 12/3.
Can I run two pieces of 12/2, using only one of the neutrals? I can't see any reason it would be any less reliable than 12/3; but expect it probably violates some code or other, though I don't know why it should.
300.3 Conductors.
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord,
According to toller :
It violates code. Code requires all conductors for a circuit to be in the same "raceway", which in the case of romex, means a single sheath. With conduit, it means the same hunk of pipe. Etc.
Principle of least surprise for renovations and circuit alteration, plus probably a few other reasons.
May also be classified as poor workmanship - wrong materials.
Sure you need to make it four wire?
...unless otherwise permitted in accordance with 300.3(B)(1) through (4).
Nick
I looked 300.3(B) up in my electrical book and it gave the example below.
If this example is okay, wouldn't mine also? Mine is rather better, since all the wires are at least in close proximity.
And do these allow what I want to do?
No
Unzip the cable (pretty easy to do with NM; almost impossible to do with UF) and run the individual conductors in a 1/2" conduit.
Bob
Yeah, great idea. Now he needs to buy and install conduit, rip apart cable, pull wires, all to save buying a roll of wire to do the job the right way. When did copper wire become so expensive?
It was his idea to not buy the wire. Putting in conduit *is* the right way. So is using the proper cable. Now he has 2 choices.
about a year ago.
Best regards, Bob
Using discrete conductors from a cable in a raceway isn't the "right" way.
Will it work? sure.
Is it safe? probably
Can you prove it? no.
These conductors are not marked so there is no way to tell exactly what they are and they are not tested outside of the cable they were made in.
I think they are marked, but I'm not sure. I'll have to check this afternoon.
Bob
Wires in cables are not marked. It is assumed that since they are 90c rated they are THHN but there is really no way to prove it, nor is there any obligation for the manufacturer to actually use a wire with THHN specs. It might turn out that the wire in Romex lacks some abrasion resistance or other property you would find in THHN. When they are making thousands of miles of Romex a year, shaving a small fraction of a penny off the cost of the wire will add up quickly so you don't know what you are getting. Cables are tested as an assembly and you can be sure they don't add anything extra beyond what it takes to get listed.
There is a practical reason not to do that. If the conductors are not in the same cable or raceway they will produce an electromagnetic field of sufficient amplitude to cause interference with radios and hearing aids. If at any point along the pathway a metallic object is between the two sets of conductors an AC current can be induced into the metallic object and inductive heating can result.
-- Tom H
I doubt it, at 60 Hz, with balanced currents in the two hots.
Nick
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Tom, is this a danger also with the ungrounded and ground-ED (i.e. hot and neutral) conductors run in the same raceway, and the ground-ING conductor in a different raceway some ten feet away?
Maybe I'm not following you but the idea is to put all of the circuits conductors in the same cable or raceway. So that their respective magnetic fields will cancel each other out to the greatest degree possible.
-- Tom H
Are we talking about non metallic raceways here? What grounding conductor are we speaking of? Is it the Equipment Grounding Conductor (EGC) of the circuit in question or is it the or the Grounding Electrode Conductor (GEC) of the entire electric service that is supplying that particular circuit?
-- Tom Horne
Were do we get the guarantee that the two hots will remain balanced in the four wire circuit? The circuit is four wires because a neutral is needed to carry the imbalance current that is the difference of the load on the two ungrounded conductors. If no difference were going to occur no neutral would be required in the circuit and it could be run in a single two wire plus ground romex cable.
-- Tom H
Specifically, it's a 240V feed from the service panel to a subpanel, with the neutral and the two hots in rigid nonmetallic conduit going through the attic of the garage, and the equipment ground in rigid metal conduit buried in (or under) the slab.
[Note: I didn't do this. I'm the fourth owner of this house; the original electrician knew what he was doing, but in between him and me, there's been work done that was somewhat less than fully Code-compliant.]HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.