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.