Re: Metallic Conduit on Roof-Tops Will Require an EGC!
5-211 Log #2293 NEC-P05
(250-118(14) Exception (New) )
Final Action: Accept in Principle
TCC Action:
See the Technical Correlating Committee Note on Proposal 5-1. The Technical Correlating Committee notes that the issue of
determining acceptability for the particular wiring method for grounding is the responsibility of the applicable Code-Making Panel.
For this proposal, Code-Making Panel 8 has the responsibility to determine if the wiring method is acceptable as proposed. The
Technical Correlating Committee refers this proposal to Code-Making Panel 8 for comment.
Submitter: Norman Smith, I.B.E.W. Local 291 / Rep. Labor
Recommendation:
Insert after Section 250.118(14).
Exception: Where metallic conduit is installed on roof tops, an equipment grounding conductor shall be provided within the raceway
and sized per Section 250.122.
Substantiation:
Metallic conduit on rooftops is exposed to extreme temperature changes and weather conditions and may lose electrical continuity at
connections and the capacity to conduct safely any fault current likely to be imposed on them.
Panel Meeting Action: Accept in Principle
Revise the text to add an exception to 250.118 located after 250.118(14) to read as follows:
Exception: Where metallic conduit is installed on rooftops, an equipment bonding conductor of the types specified in 250.118(1) shall
be provided within the raceway and sized per Section 250.122.
Panel Statement:
This issue has been raised with varying amounts of technical substantiation for several Code cycles. The problem being identified
really relates to an unsuitable use and installation of this wiring method leading to these conditions. The panel understands the safety
concerns raised by the submitter's substantiation. CMP 5 requests the Technical Correlating Committee to refer this proposal to CMP 8
for action.
Number Eligible to Vote: 16
Affirmative: 12 Negative: 4 Ballot Results:
Explanation of Negative:
BRETT: The submitter has not provided technical substantiation for this proposed change. His statement is true that weather conditions
exist on rooftops. However, the present language in the code already covers these installations. Proper installations in accordance with
present code language take all these conditions into consideration.
The panel actions taken have not been substantiated. All proposals over the past several code cycles have cited workmanship issues
relating to small sizes (1/2 and 3/4) of metallic and nonmetallic unthreaded raceways being improperly installed.
The code has always required raceways to be properly supported and secured. 300.7(B) states: "Raceways shall be provided with
expansion fittings where necessary to compensate for thermal expansion and contraction." All raceways are required to be listed. RMC,
IMC and EMT are listed galvanized steel raceways and provide corrosion protection. Physical protection is also adequately addressed in
each code article.
The change as accepted would require all metal raceways to have an equipment grounding conductor installed including threaded
raceways up to trade size 6. What substantiation has been provided to require threaded metal raceways to have a supplemental equipment
grounding conductor? These requirements would also apply regardless of the purpose i.e., Service, Feeder, Branch circuit, etc.
The change is overly restrictive and the responsibility should remain with the designer. Please reject this proposal.
DOBROWSKY: The submitter's substantiation indicates that the wiring method chosen for this specific installation was not suitable.
Even if an equipment bonding conductor was installed if the wiring method was damaged, the conductors would be exposed creating a
hazard. Many existing wiring methods have been safely used for many years without an additional equipment bonding conductor.
SKUGGEVIG: The same harsh conditions that jeopardize the electrical continuity of the metal raceway will also act to cause failure of
the equipment grounding conductor (wire) after the raceway has failed leaving sections of the wires exposed. A supplementary
equipment grounding conductor might be unable to sufficiently improve the overall reliability of the dual grounding path, and does not
address the problem of keeping all of the conductors fully protected inside of an intact raceway. The problem of dealing with a harsh
environment cannot be solved by simply adding another vulnerable and marginally protected component into the harsh environment.
The metal raceway must be made more resistant to failure in the harsh environment if it is to be used in this environment. If this is
accomplished, then there is nothing wrong with the metal raceway's ability to serve as the sole grounding path, without a supplementary
grounding conductor. In addition, see my Comment on Affirmative on Proposal 5-1 regarding changing the term "equipment grounding
conductor" to "equipment bonding conductor".
STEINMAN: There is no technical substantiation provided to make this change. The substantiation provided by the submitter is a
violation of 300.7(B), "raceways shall be provided with expansion fittings where necessary to compensate for thermal expansion and
contraction." Properly installed, metallic raceway systems are good equipment grounding paths.
Comment on Affirmative:
RAPPAPORT: The word "conduit" should be replaced with the generic term "raceway" in order to include electrical metallic tubing.
TOOMER: The panel recognized there is a problem, therefore since it has the authority, it should require an equipment bonding
conductor be installed for safety.
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