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NEC Changes For #14 Ampacity

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    #16
    Originally posted by peter d View Post
    Have you ever held a 14/2 NM cable with a steady 12 to 15 amp load on it? I have and it gets pretty warm. While not an overt hazard, that kind of heating for an extended period of time will degrade the insulation.
    Warm might be 100-110*F. The wire insulation is good for a minimum of 194*F. Anyone who has seen #14 loaded to 20amp knows it doesnt get anywhere near that temperature.
    Our comedian shamelessly joked about a blackout. Talk about dark humor.

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      #17
      Originally posted by peter d View Post
      So you're both saying it's acceptable to load #14 wire to 20 amps or more?
      Technically it is, otherwise Canada wouldn't be doing it.


      FWIW 1.5mm2 wire (thinner then our 2.08mm2 14 gauge) is allowed to carry 15amps inside a wall at 70*C.
      Our comedian shamelessly joked about a blackout. Talk about dark humor.

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        #18
        Originally posted by mbrooke View Post
        Warm might be 100-110*F. The wire insulation is good for a minimum of 194*F. Anyone who has seen #14 loaded to 20amp knows it doesnt get anywhere near that temperature.
        And your point is? I2R losses are real and that's what you discount when you want to reduce ampacity to the bare minimum.

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          #19
          Originally posted by mbrooke View Post
          Technically it is, otherwise Canada wouldn't be doing it.
          Good for them. We're not in Canada so it doesn't affect me or how I wire things.


          FWIW 1.5mm2 wire (thinner then our 2.08mm2 14 gauge) is allowed to carry 15amps inside a wall at 70*C.
          So what?

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            #20
            Originally posted by peter d View Post
            So you're both saying it's acceptable to load #14 wire to 20 amps or more?
            The older I get the more I want things to be easy and the less I care about what happens in a hundred years, so yes, I good with it.
            If Billy Idol is on your playlist go reevaluate your life.

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              #21
              Originally posted by peter d View Post
              And your point is? I2R losses are real and that's what you discount when you want to reduce ampacity to the bare minimum.
              I could wire with #10 for 20amps and if my run is long enough voltage drop will still get me.



              Originally posted by peter d View Post
              Good for them. We're not in Canada so it doesn't affect me or how I wire things.

              So what?
              But Canada has proven it wont burn down someones home, which I think the OP was wondering about.
              Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                #22
                From the 1918 NEC:

                http://antiquesockets.com/NEC-LIB/NEC-1918.pdf
                Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                  #23
                  i am not concerned bout why CEC changed ampacity for #14 wire, i am want to see the evidence as to why NEC changed it between NEC2002 and NEC2008 and why NEC has the 15A OCD restriction.

                  i see some are digging into the 125% bit. but let me clarify, if the OCD's dont actually trip until 125% of their rating (which also makes no sense) and NEC restricts ampacity of romex to the 60C column, then putting a #12 onto a 20A OCD would allow the #12 to run above the 60C ampacity #, which by the NEC is a violation (not a wire issue, just a violation by NEC verbiage).

                  as for I^2R, #14 @ 100ft @ 20A is 1W/ft which is a fairly low density exothermic thing. within say romex cable the wire insulation is subject to 1W/ft directly and 1W/ft indirectly and that heat is in a fairly poor heatsink (romex sheeting), yet the cable is rated 90C. given that NEC allows >15A OCD on #14 wire via special exceptions, why is I^2R an issue?

                  i am basically just looking for the evidence that supports the NEC verbiage, etc. making the rules on the "just because" or "runs cooler" basis doesnt make sense to me.

                  NEC 240.4 Protection of Conductors

                  Conductors, other than flexible cords, flexible cables, and
                  fixture wires, shall be protected against overcurrent in
                  accordance with their ampacities specified in 310.15, unless
                  otherwise permitted or required in 240.4(A) through (G).
                  this 240.4 keeps throwing me off. is Romex a "flexible cable" ?


                  and post #22, oddly the amps per circular mil seems to go down as the wire size goes up. ~3.6mA/cmil for #14 down to ~1.6mA/cmil for #5 wire.
                  Last edited by FionaZuppa; 09-03-15, 08:42 PM.

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                    #24
                    Originally posted by peter d View Post
                    So you're both saying it's acceptable to load #14 wire to 20 amps or more?
                    I simply made a statement about the insulation not being degraded when it is operating below its listed temperature rating.

                    Given allowances for 'non-general purpose' circuits (e.g Table 240.4(G)) and ambient temperature adjustments, it is possible to find NEC compliant applications that permit #14 wire to be loaded to 20A or more.
                    Just because you can, doesn't mean you should.

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                      #25
                      Originally posted by FionaZuppa View Post
                      i am not concerned bout why CEC changed ampacity for #14 wire, i am want to see the evidence as to why NEC changed it between NEC2002 and NEC2008 and why NEC has the 15A OCD restriction.

                      i see some are digging into the 125% bit. but let me clarify, if the OCD's dont actually trip until 125% of their rating (which also makes no sense) and NEC restricts ampacity of romex to the 60C column, then putting a #12 onto a 20A OCD would allow the #12 to run above the 60C ampacity #, which by the NEC is a violation (not a wire issue, just a violation by NEC verbiage).

                      as for I^2R, #14 @ 100ft @ 20A is 1W/ft which is a fairly low density exothermic thing. within say romex cable the wire insulation is subject to 1W/ft directly and 1W/ft indirectly and that heat is in a fairly poor heatsink (romex sheeting), yet the cable is rated 90C. given that NEC allows >15A OCD on #14 wire via special exceptions, why is I^2R an issue?

                      i am basically just looking for the evidence that supports the NEC verbiage, etc. making the rules on the "just because" or "runs cooler" basis doesnt make sense to me.


                      this 240.4 keeps throwing me off. is Romex a "flexible cable" ?


                      and post #22, oddly the amps per circular mil seems to go down as the wire size goes up. ~3.6mA/cmil for #14 down to ~


                      If I remember correctly it had something to do with an equation from the IEEE book that was used to derive it.

                      But you have to keep this mind, the NEC wire tables are very conservative assuming worse case scenario with a safety factor on top of that. Whether its 15 or 20amps at 60*C is more relative and arbitrary then anything else.

                      Trust me, I wonder the same behind the change.
                      Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                        #26
                        sorry couldnt make edit in time, here's more

                        and post #22, oddly the amps per circular mil seems to go down as the wire size goes up. ~3.6mA/cmil for #14 down to ~1.6mA/cmil for #5 wire. a significnat decrease in allowed current, but kinda makes sense as heat is function of I^2. but oddly the table allows for about 1W/ft in #5 @55A, but in #14 (restrcited to 15A) its only 0.57W/ft (@100ft). allowing 20A on #14 would be almost identical heat density, thus why i am baffled as to why #14 is so restricted.

                        the ampacities (and thus allowed OCD sizes) should be chosen so that the allowed heat density is about the same across all wire sizes. 1.02W/ft @100ft seems like a good std. if the wire is subject to more than 1.02W/ft @100ft then next wire size should be used. this basically defines max OCD to be used, thus the table would look something like

                        #14 20A
                        #12
                        Last edited by FionaZuppa; 09-03-15, 09:01 PM.

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                          #27
                          this 240.4 keeps throwing me off. is Romex a "flexible cable" ?
                          No, NM-B is classified as a type of building wiring method. Flexible cord would be like SJOW which is not for building wiring.


                          and post #22, oddly the amps per circular mil seems to go down as the wire size goes up. ~3.6mA/cmil for #14 down to ~1.6mA/cmil for #5 wire.
                          Larger wires dissipate less heat relative to smaller wire.
                          Our comedian shamelessly joked about a blackout. Talk about dark humor.

                          Comment


                            #28
                            Originally posted by FionaZuppa View Post
                            sorry couldnt make edit in time, here's more

                            and post #22, oddly the amps per circular mil seems to go down as the wire size goes up. ~3.6mA/cmil for #14 down to ~1.6mA/cmil for #5 wire. a significnat decrease in allowed current, but kinda makes sense as heat is function of I^2. but oddly the table allows for about 1W/ft in #5 @55A, but in #14 (restrcited to 15A) its only 0.57W/ft (@100ft). allowing 20A on #14 would be almost identical heat density, thus why i am baffled as to why #14 is so restricted.
                            Question is, restricted compared to what? Keep in mind the material around the wire plays the biggest role.

                            In the IEC for example 2.5mm2 twin and earth cable (similar to NM) is rated 27amps clipped direct (stapled to wood no insulation), 20amps in contact with insulation and in BS7671 13.5amps when surrounded by dense thermal insulation. This is all governed by the cable's ability to dissipate heat.
                            Our comedian shamelessly joked about a blackout. Talk about dark humor.

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                              #29
                              Originally posted by FionaZuppa View Post
                              this 240.4 keeps throwing me off. is Romex a "flexible cable" ?
                              No. Those other types of cables/cords/wires ampacities are covered in different tables in other sections. See 400 and 402. NM/Romex is in 310.15 and 334.
                              "Electricity is really just organized lightning." George Carlin


                              Derek

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                                #30
                                again , sorry, my edit time was reached.

                                what i am suggesting is a std in heat density. ~1.02W/ft @ 100ft of wire seems like a good # (just as example here). however, the current ampacity table does not provide a constant heat density.

                                but if it were constant across all wire sizes then the table would look something like this:

                                (rounded up to nearest whole)
                                #14 20
                                #12 25
                                #11 28
                                #10 32
                                #9 36
                                #8 40
                                #7 45
                                #6 50
                                #5 57
                                #4 64
                                #3 71
                                #2 80
                                #1 92
                                #0 101

                                these max amps per wire size based on 1.02W/ft @100ft. in NEC2011 #1 is 110A in 60C column, thats 1.45W/ft @100ft, and #4 is 1.23W/ft @ 100ft. its not constant.

                                heatsink of insulation area only?
                                ok
                                #1 would be 10.9sq.in/ft
                                #4 would be 7.698sq.in/ft

                                thus the heatsink area density is
                                #1 0.133W/sq.in.
                                #4 0.160W/sq.in.

                                not even the heatsink area density is constant.
                                Last edited by FionaZuppa; 09-03-15, 09:24 PM.

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