Derating Wire | 90% Recommended |

Required ampacity = 45A continuous × 1.25 = 56.25A

Table 310.15(C)(1): 7–9 conductors = 70% 47.85A × 0.70 = 33.5A derating wire

Continuous load must not exceed 80% of the derated ampacity (or conversely, the derated ampacity must be ≥ 125% of the continuous load). Required ampacity = 45A continuous × 1

At first glance, electrical wiring seems simple. You look up a wire gauge (e.g., 10 AWG) on an ampacity chart, see it handles 30 amps, and select a 30A breaker. But what happens when that wire is run through a 140°F attic? What if four of those wires are bundled inside a conduit? What if the equipment is installed at 10,000 feet of altitude? But what happens when that wire is run

| Number of Conductors | Percent of Ampacity | |----------------------|---------------------| | 1–3 | 100% | | 4–6 | 80% | | 7–9 | 70% | | 10–20 | 50% | | 21–30 | 45% | | 31–40 | 40% |