To calculate the maximum current in an insulated wire when there are more than 3 current carrying wire conductors in the same raceway or cable, first, find the
maximum allowable current
for a raceway or cable with less than 3 current carrying wire conductors, then multiply that maximum current by the percentage number from the
Adjustment Factors for More Than 3 Current Carrying Conductors Chart below and divide by 100.
Maximum Current Adjustment Factors
for More Than 3 Current‑Carrying Conductors
in a Raceway or Cable
| Number of Conductors in a Raceway |
Percent of Total Value |
| 4 – 6 |
80 |
| 7 – 9 |
70 |
| 10 – 20 |
50 |
| 21 – 30 |
45 |
| 31 – 40 |
40 |
| 41 or Above |
35 |
Table 310.15(C)(1), 2020 NEC®
WARNING: For safety, call a licensed electrician and consult the NEC®. All licensed electricians have passed examinations
covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages.