(Here is the scenerio)A new school construction project consisting of (1)100a 3 phase 4 wire 120/208v panelboard feeding small mechanical equipment and receptacles,(1) 150a 3 phase 120/ 208v feeding receptacles/equipment.All branch wiring is fed from underground passing through a 6x6x36" gutter.Then VIA 2" emt conduit approx 30" long to panels . (1) 2" EMT per panel.The 150a panel has #12 Thhn 35 hots & 25 Nuetrals ,15 grounds in the 2" raceway.The 150a panel has #12 Thhn 18 hots & 12 Neutrals , 10 grounds in the 2" emt raceway.QUESTION (1) are the nuetrals required to be counted as current carrying conductors? (2) Is the derated ampacity of the conductor applied to the calculated load or overcurrent protection of the cicuit?(3)I am also confused as to the 30 current carrying conductors max in a metal wire way per article 362-5 please clarify.Whats the easiest fix here ? clarification of these codes would greatly be appreciated!
Wire derating per 310-15(b)(2)(a)
- Thread starter mitch8990
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Wire derating per 310-15(b)(2)(a)
Some will, others may not. For any single-phase, two-wire (plus ground), the neutral counts. For any three-phase, four wire (plus ground), the neutral does not count. For any single-phase, multi-wire (i.e., two hots, one neutral, one ground), the neutral does not count.
Neither. It applies to the wire. In other words, a pair of wires that might be good enough to handle 30 amps, if routed alone, might only be able to handle 15 amps, if routed with 8 other current-carrying conductors. The steps are (1) You determine the load. (2) You pick a wire that can carry that much load, keeping in mind that the ability of a wire to carry load gets smaller if you route many wires together, and (3) You pick an overcurrent device that will protect the selected wire.
You must still be using the 1999 version. In the 2002 version, that requirement was moved to 376.22, and was re-worded. It now says that (2) The total cross-sectional area of the wires cannot be more than 20 % of the area of the wireway (not a change from 1999), and (2) You only have to derate if there are more than 30 conductors.
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