So I finished pulling a three-phrase feeder to a power panel, No. 2 250 Kcmil per leg, when the inspector said, “Where is your neutral?” “There is no neutral,” said I; “This is a feeder to a three-phase, three-wire Delta power panelboard.” The inspector said, “Yes, but 200.2 says you must pull a grounded conductor with that feeder.”
Well, I looked up that laundry list in 200.2 and, sure enough, this requirement appears: “All premises wiring systems other than … shall have a grounded conductor that is identified in accordance with 200.6.” None of the “other than” situations applied to my job.
The system does not have a grounded conductor, so what sense does this requirement make? And how can I pull a neutral when the three-phase delta ungrounded system has no neutral?
Going back to the 1971 NEC, Section 200-5(b) reads the following, in part: “Polyphase circuits need not have one conductor grounded …”. So, under the 1971 and earlier editions of the NEC, this conflict with the inspector would not have arisen.
In the Walter R. Stone editorial rewrite for the 1974 NEC, the above-quoted phrase was deleted. The only explanation is in the cross-index to the changes, in the back of the Preprint Part I, where 200-5(b) is indicated as “(Deleted).” Supposedly the Code-Making Panels reviewed Stone’s work, but there is no mention of this change in Preprint Part II, Proposed Amendments for the 1974 National Electrical Code. The date on the 1974 NEC was changed to 1975.
Here we have a change in the NEC, which deleted a useful requirement, and for which there is no documented reason (as if there could be a logical reason) for the deletion—another dead-end search into the history of the NEC.
On another subject, there is some confusion regarding the enclosing of various parts of the wiring for three-way switches when enclosed in metal raceways or metal-clad cables. This does not pertain to Type MI Cable with a non-magnetic sheath, nor to aluminum conduit or aluminum sheathed cables.
The basic requirement is found in 300.3(B): “(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, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).”
The other NEC requirement having effect here is in 300.20: “300.20 Induced Currents in Metal Enclosures or Metal Raceways. (A) Conductors Grouped Together. Where conductors carrying alternating current are installed in metal enclosures or metal raceways, they shall be arranged so as to avoid heating the surrounding metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.”
Although not specifically covered by the Code, a two-wire drop from a lighting outlet to a switch location, containing a hot and a switch leg satisfies the Code, even though the grounded conductor is not included. The magnetic fields around the two conductors cancel each other out, so there is no heating of the enclosing metal by induction.
There are four conductors used in three-way switch wiring: 1. The neutral (grounded conductor) that terminates at the outlet; 2. The hot that terminates at the first three-way; 3. The travelers, which are the two conductors between the two three-way switches and 4. The switch leg, which is the return from the second three-way to the outlet.
There are many arrangements of the outlet(s) and the two switches. Following these rules will help in determining the number and type of conductors in each connecting run of a three-way installation: 1. The neutral must always be in the same raceway or cable with the hot or with the switch leg. 2. The travelers must always be in the same raceway or cable with the hot or the switch leg.
One condition that requires a four-wire cable is where there are two switched outlets, and each of the two three-way switches are connected to one of the outlets. Assuming the home run terminates at the first outlet, the connection between the two outlets will include the travelers, the neutral and the switch leg. All of the other arrangements can be wired with two-wire or three-wire cable.
To Code Comments readers:
This column will be my last. The first was in January 1980, for a total of 326, and I never missed a deadline. My purpose has been to cause the reader to think about the NEC and the way in which it is developed. Sometimes I have put forth strange interpretations of the Code to illustrate what an inexperienced inspector might come up with a literal reading.
My six months to live with Myelodysplastic Syndrome is running out, and I wanted to say goodbye while I could. My thanks to those of you who provided feedback and to those who accepted my writings with no objection. I have enjoyed the work and have been proud to be listed on the masthead of ELECTRICAL CONTRACTOR magazine.
—W. Creighton Schwan, P.E.
Editor’s note: We are sad to report that Creighton passed away on Dec. 16, 2006. Please see Web Exclusives for a complete obituary.