Link — Derating Wire

At 4,000m, air density is ~60% of sea level. Cooling efficiency plummets. Many engineers forget this for mountain-top radio towers or mining equipment.

Identify the wire you are using.

Remember the golden rule of derating:

Suddenly, the 30A wire becomes a 15A fire hazard.

Wire is sold with a standard ampacity rating (e.g., 12 AWG copper is rated for 20 amps). However, this rating assumes ideal conditions: a single wire, in open air, at a specific ambient temperature (usually 86°F / 30°C). derating wire

| Trap | Consequence | Prevention | |------|-------------|------------| | Derating from 75°C column instead of 90°C | Undersized wire by ~20% | Always derate from insulation rating | | Forgetting to count neutrals in non-linear loads | Severe overheating in harmonic-rich circuits | Measure THD; count neutral as CCC if > 50% of phase current | | Assuming free air is the same as conduit | Overrating wire by 30-40% | Use correct table (310.17 for free air vs. 310.16 for raceway) | | Ignoring rooftop solar heating | Insulation melting on summer days | Add 25°C to ambient for rooftop | | Applying derating after 125% continuous factor (double penalty) | Oversizing unnecessarily | Apply derating first, then check against 125% of load | | Using 60°C column for old breakers with modern wire | Code violation | Match termination rating (usually 75°C) |

To properly derate, follow this order of operations. At 4,000m, air density is ~60% of sea level

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

32.16A < 56.25A → FAIL. Solution: Increase to 4 AWG (base 95A) and recalculate. Identify the wire you are using