Section 250-60(c) in the National Electrical Code has permitted Type SE cable with an uninsulated grounded conductor for grounding the frame of a dryer, range, etc., for many years because of the war emergency.
This information is found in the Foreword contained in the Supplement to the 1940 National Electrical Code, Standard of the National Board of Fire Underwriters for Electric Wiring and Apparatus as recommended by the National Fire Protection Association. This supplement was an American Standard 1940 Edition, approved August 7, 1940 by The American Standards Association.
On July 10, 1942 an Interim Amendment No. 53 was approved for a new Section 2559 as follows:
"Frames of Electric Ranges. Frames of electric ranges which are to be grounded may be grounded by any of the means provided for in sections 2556 and 2558. If not so grounded, and if not connected to or in contact with other grounded equipment or structures, they may be grounded by connection to the grounded circuit conductor."
This action was intended to save copper material so that it could be used in ways to defend our country. I'm sure you'll agree that Type NM nonmetallic sheathed cable, manufactured at that time was without an equipment grounding conductor, and where it did contain an equipment grounding conductor, it was smaller than the ungrounded conductors. Many feel that there is no technical reason for not permitting Types NM, NMC or UF cable assemblies to be used in the same manner as a Type SE cable where the equipment grounding conductor is sized in accordance with Section 250-95.
In the 1978 "Preprint" CMP-5 rejected Proposal No. 82 which was submitted to amend this section as follows:
"(c) The grounded conductor is insulated; or the grounded conductor is uninsulated and part of a cable assembly and the branch circuit originates at the service equipment."
The submitter supplied the following supporting comment: "The use of Type SE cable as specified in the section seems to deny the use of NM, NMC and UF with bare ground for these installations. The only differences in the cables would be temperature limitations on circuit conductor insulation and outer cover insulating values. Types NM, NMC and UF would have no special application for terminating the conductors. The use of NM, NMC, and UF would facilitate installation by having all materials consistent with those for dry indoor installations."
CMP-5 voted unanimously to reject this Proposal. Their comment was as follows: "Panel feels that the special permission should not be expanded to other type of cables."
The NEC-TCD did not exist at that time; therefore Public Comments could not be addressed.
For the 1986 NEC-TCR, Proposal Nos. 5-110 and 5-137 were submitted requesting that Types UF, NM and NMC nonmetallic sheathed cable assemblies be added to Section 250-60(c). CMP-5 rejected them with the following Panel Comment. "The Panel does not feel that the present rule should be expanded to permit equipment grounding conductor to serve as grounded circuit conductors." Only one TCD Public Comment No. 5-39 was submitted. CMP-5 rejected this comment because they said it was not relevant to the subject of the original Proposal 5-137.
It should be noted that the above is my personal opinion and represents a personal response as requested. My opinion must not be considered as a Formal Interpretation of the NEC and is not to be considered as an official position of the NFPA, the NEC Correlating Committee or any of its panels, or the IAEI.
Very truly yours,
Joe Tedesco, Codes, Standards, and
cc: J. Philip Simmons, Executive Director