IEEE-SA SCC-18 Report by Representatives to NFPA NEC CMP-6 January 6-8, 2010 on Actions Taken on Proposals by CMP-6 for NEC 2011 ROC Prepared by

Transcription

1 IEEE-SA SCC-18 Report by Representatives to NFPA NEC CMP-6 January 6-8, 2010 on Actions Taken on Proposals by CMP-6 for NEC 2011 ROC Prepared by Bruce McClung, McSquared Electrical Consulting LLC and Don Voltz, British Petroleum

2 CMP-6 Summary 101 Proposals Submitted/Received by CMP-6 Accepted 50 (A) Rejected 33 (R) Accepted in Principle 9 (AIP) Accepted Part 4 (AP) Accepted in Principle and Part 4 (APP) Hold 1 (H)

3 CMP-6 Summary (Cont d) Four Categories of Comments dominated the review/actions activity of CMP-6 Rewrite of Article 310, 400 and Annex B; and Harmonization of NEC with CEC Article 310 and Annex B Non-shielded MV power cable Ampacity of Conductors on Rooftops Single Phase Dwelling Services and Feeders

4 CMP-6 Summary (Cont d) Rewrite of Article 310, 400 and Annex B; and Harmonization of NEC with CEC Article 310 and Annex B, (being presented for information only): ROP actions were undertaken mainly to locate Tables with same section/articles as text and to harmonize ampacities between NEC and CEC. Comment 6-21, (AIP with unanimous vote), illustrates that all Ampacity Tables will show dual identity for the next two Code cycles: such as Table (B)(6) formerly Table

5 CMP-6 Summary (Cont d) Non-shielded MV power cable, (being presented for information only): Comment Code Source Panel Panel Vote *Designates IEEE Action FOR-Against-Abstain A 11* R 7* AIP 11* AIPP 11*----0 Illustrates that efforts to restore use of non-shielded MV power cable for use in industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation will be in the NEC 2011.

6 CMP-6 ER s Voted AGAINST the Panel Vote Seeks Concurrence From SCC-18 Membership Ampacity of Conductors on Rooftops, (IEEE-SA SCC 18 ER s need concurrence and support for voting against the CMP-6): Comment Code Source Panel Panel Vote *Designates IEEE Action FOR-AGAINST-ABSTAIN (B)(2)(c)&FPN R * Table (B)(2)(c) (B)(2)(c)&FPN R * Table (B)(2)(c) (B)(2)(c)&FPN R * Table (B)(2)(c) All three comments pertain to ROP Proposal 6-70 which IEEE-SA SCC 18 directed CMP-6 ER s to act to accept proposals that call for deleting (B)(2)(c). Voting against the Panel on all three proposals above will be acting to accept all four proposals which would delete (B)(2)(c) from the NEC CMP-6 ER s suggest the statement to be found on the next slide to submit with vote against the Panel vote to reject the proposals shown above.. (Cont d)

7 Statement Suggested by CMP-6 ER s to Accompany Negative Votes on Comment Ballot for Each of Comments 6-41, 6-43, 6-44 and 6-47 (Cont d) Code Panel 6 has now addressed the issue of solar radiation effects on the ampacity of wire in conduits (i.e. circular raceways) and Type MC Cable for rooftop applications since the 2005 cycle. The answer was to insert Table (B)(2)(c) Ambient Temperature Adjustment for Conduits Exposed to Sunlight On or Above Rooftops The data submitted to the Panel over this period has been developed from one site specific application where it was recognized that the intense sunlight had immediate effect on the temperature rise in the conduit and Type MC Cable. It should be noted that this testing was done on non-energized conductors in conduit and in Type MC Cable and that the data submitted did not address any long term aging effects. Yes, it gets hot inside the conduit or cable but to this point there has been no data presented showing any detrimental effects. Also, at no point during this period has the data submitted to the Panel been independently (i.e. third-party) verified. To this point the Panel has excluded Type MC Cable from Table (B)(2)(c) as it recognized that there was insufficient data submitted for inclusion. The panel should continue to do so.

8 Statement Suggested by CMP-6 ER s to Accompany Negative Votes on Comment Ballot for Each of Comments 6-41, 6-43, 6-44 and 6-47 Cont d) For years now, the electrical industry has safely used the allowable ampacity in Table including all adjustment factors, especially temperature, to size conductors in conduits and Type MC Cable for rooftop applications. Over this period, there has been no reported evidence of conductor or cable degradation due to the increased temperature rise inside the conduit or Type MC Cable. If there was a problem, you would think failure data would have been included in the many reports submitted to the panel. Therefore, the present method of sizing conductors in conduit or Type MC Cable for rooftop applications using the time honored allowable ampacity values in Table with appropriate adjustments is adequate.

9 Statement Suggested by CMP-6 ER s to Accompany Negative Votes on Comment Ballot for Each of Comments 6-41, 6-43, 6-44 and 6-47 (Cont d) Rather than relying on experimental data to size conductors in conduit and Type MC Cable for rooftop applications or using the time honored allowable ampacity values found in Table , the ampacity values can be calculated using the electrical/thermal circuit found in the IEEE (R2006) IEEE Standard Power Cable Ampacity Tables which includes the air space inside the conduit. The ampacity values contained in this standard are based on the Neher-McGrath calculation method. For conductors in horizontal conduit or cable in free air as would be found on rooftops, the ampacity calculation includes the effect of sun (solar radiation) and wind. From Table 29 of that standard, the following are some representative ampacity values for three, 600V copper conductors in horizontal conduit in free air based on a conductor temperature of 90 C and an ambient temperature of 40 C.

10 Statement Suggested by CMP-6 ER s to Accompany Negative Votes on Comment Ballot for Each of Comments 6-41, 6-43, 6-44 and 6-47 From IEEE (R2006 From Table #12 - No Sun, No Wind (0 ft/s) - 28 A #12 - No Sun, 2 ft/s - 29 A #12 - Full Sun, No Wind (0 ft/s) - 21 A #12 - Full Sun, 2 ft/s - 24 A #10 - No Sun, No Wind (0 ft/s) - 37 A #10 - No Sun, 2 ft/s - 38 A #10 - Full Sun, No Wind (0 ft/s) - 27 A #10 - Full Sun, 2 ft/s - 31 A Using the temperature adjustment factor of 0.88 for a 40 C ambient temperature for comparison, the 90 C allowable ampacity values from Table are 26.4 A for a #12 and 35.2 A for a #10. As one can see, the IEEE values are a little less in the full sun cases than the adjusted allowable ampacity from Table but are more than the adjusted values using Table (B)(2)(c). In any case, the Panel should reconsider their position on this issue and render their judgment based on scientific methods versus experimental methods from a single test site.

11 CMP-6 Summary (Cont d) Single Phase Dwelling Services and Feeders, (being presented for information only): Comment Code Source Panel Panel Vote *Designates IEEE Action FOR-AGAINST-ABSTAIN 6-55 by Cline (B)(6) AIP 9* by Pauley Proposed (B)(7) AIPP 8* Both comments pertain to CMP-6 Proposal 6-83a to the ROP in an attempt to clarify the original intent of Table (B)(6). This table was introduced many years ago by the utility companies to take advantage of load diversity in individual dwelling units of one family, two family and multifamily dwelling units. Originally it was described that the feeder conductors to a dwelling unit shall not be required to have an allowable ampacity greater than their service entrance conductors. Like table the ampacities listed for conductor types and sizes in Table (B)(6) are those values established by historic time-honored usage. Changes are occurring each Code cycle. The continual changes are creating misunderstandings. CMP-6 spent an inordinately amount of time on this issue- indicative of the overall problems with it as written. Improvements were made by combining the best of both comments.. (Cont d)

12 CMP-6 Summary (Cont d) Single Phase Dwelling Services and Feeders, (being presented for information only): NFPA NEC does not include any means for adjusting ampacity where main power panel is a significant distance from the service entrance disconnect or covered with household thermal insulation. Expect improvements to be proposed for this issue during 2014 Code cycle. Meanwhile IEEE Members involved in determining ampacity and sizing conductors for individual dwelling units of one family, two family and multi-family dwelling units should follow the IEEE Standard 835 NFPA NEC Definitions does not include any definition for Diversity Factor. Diversity Factor is described/defined in IEEE Standard 100 as the ratio of the sum of the individual non-coincident maximum demands of various subdivisions of the system to the maximum demand of the complete system. The diversity factor is always 1 or greater. Load Diversity refers to the percent of time available that a machine, piece of equipment, or facility has its maximum or nominal load or demand; i.e. a 70% diversity means that the device in question operates at its maximum or nominal load level 70% of the time that it is connected and turned on. Where there is no load diversity the device operates at maximum or nominal load 100% of the time.