Adjustment Factors for More Than Three Current-Carrying Conductors
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Definitely not.
- Location
- Illinois
- Occupation
- retired electrician
The table ampacities are based on not more than 3 current carrying conductors in a raceway or cable. When there are more than 3 current carrying conductors in a raceway or cable, you are required to adjust the ampacity per Table 310.15(B)(3)(a) or Table 310.15(C)(1) in the 2020 code.
Each current carrying conductor contributes heat to the other conductors based on the I²R losses in the conductor.
Each current carrying conductor contributes heat to the other conductors based on the I²R losses in the conductor.
Carultch
Senior Member
- Location
- Massachusetts
Every individual conductor that carries current counts as a conductor for purposes of using this table, regardless of whether you mechanically group them in cables within a raceway, or whether you have individual conductors in the raceway.
The ways that conductors don't count toward this total:
1. EGC's, GEC's, SSBJ's and any other wire that could be green or bare, and isn't meant to carry current, doesn't count.
2. Conductors that are set up to never carry current simultaneously, do not have to both count together. For instance, travelers in a 3-way switch circuit, where only 1 or 2 wires will carry current at any given time. Another example I would expect, but I'll defer to others to confirm, is heating and air conditioning, where the thermostat only allows one of the systems to operate at any given time.
3. Whether neutral counts or doesn't count, depends on a lot of specifics of the circuit. The short answer is that if it is possible for the full power to be only carried on the ungrounded conductors, and harmonics are insignificant, then neutral doesn't count.
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