Topic: 3/8 F M T usage

User: BIG BIRD, Location: Birdland, San Diego

Asked on: Monday, January 13, 2025 at 1:20 pm EST
Answered on: Thursday, March 6, 2025 at 7:15 am EST

Question: Good day .Happy New Year !For this question, I need some assistance on Code intent :Are 4 #12 THHN conductors allowed in 3/8" FMT with outside fittings ?I came up with yes .The cross-sectional area of 4 exceeds percent fill .FMT does not reference percent fill in 360 .It seems to intentionally leave it out .Maximum of 4 because TABLE 348.22 says 3 + 1 with no limit imposed by Chapter 9 ,In 360.22(A), 1/2 inch and 3/4 inch are specifically written to refence Chapter 9 Table 1 .Then in 360.22(B), 3/8 says Table 348.22A reason I think that 40% fill was intentionally left out is the short run .360.12 Uses Not Permitted. FMT shall not be used as follows:(6) In lengths over 1.8 m (6 ft),360.22 Number of Conductors.(A) FMT - Metric Designators 16 and 21 (Trade Sizes ½ and ¾). The number of conductors in metric designators 16 (trade size ½) and 21 (trade size¾) shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9.Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number ofcables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.page 70-178(B) FMT Metric Designator 12 (Trade Size3/8). The number of conductors in metric designator 12 (trade size 3/8) shall not exceed that permitted in Table 348.22.I see that as saying specifically to use TABLE 348.22 . (ONLY)If using words of 348.22 was the intention, stating 348.22 would be easier .page 70- xxxTable 348.22 Maximum Number of Insulated Conductors in Metric Designator 12 (Trade Size3/8) Flexible Metal Conduit (FMC)The TABLE says the answer is "4"3 + 1 ( with no limit imposed by percent fill )page 70-xxx Chapter 9 Table 348 percent Fill For FMCPage 70-xxx 348.22Page 70-xxx Table 348.22Page 70-xxx Chapter 9 Table 5 for Areapage 70-xxxFMT uses FMC TableThe asterisk denotes adding one more CONDUCTOR3 + 1= 4FMT SAYS USE TABLE 348.22, SO USE THE TABLE MAX IT OUT .ARTICLE 360Flexible Metallic Tubing: Type FMT#12 x 4 is0.0133in^2 x 4 =0.0532in^2 which is over the 0.046in^2 for 3/8" FMCThe percent fill looks like it was intentionally left out by saying that FMTfollows Table 348.22 and not words of 348.22 .If "percent fill" is needed, the diction that leaves out 348.22 should change .348.22 Number of Conductors. The number of conductorsshall not exceed that permitted by the percentage fill specified inTable 1, Chapter 9, or as permitted in Table 348.22, or for metricdesignator 12 (trade size3/8).Cables shall be permitted to be installed where such use isnot prohibited by the respective cable articles. The number ofcables shall not exceed the allowable percentage fill specified inTable 1, Chapter 9.0.0532sqin - 0.046sqin = 0.0072sqinRight is right and wrong is wrong .Chapter 9 Table 1 note (7) is nonapplicable .I'd like to figure out if the principle of 0.8 rounding from Chapter 9 Table 1 (7) can apply for 72 ten thousandths of an in^2 per Code as written .Table 1 Percent of Cross Section of Conduit and Tubingfor Conductors and CablesNotes to tables(7) ·when calculating the maximum number of conductors orcables permitted in a conduit or tubing, all of the samesize (total cross-sectional area including insulation), thenext higher whole number shall be used to determine themaximum number of conductors permitted when the calculationresults in a decimal greater than or equal to 0.8.When calculating the size for conduit or tubing permittedfor a single conductor, one conductor shall be permittedwhen the calculation results in a decimal greater than orequal to 0.8.Page number xxx because the information is "steady" for different years .0.0532in^2 - 0.046in^2 = 0.0072in^2Since a little bit of knowledge is dangerous, I'm trying to be safer .