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Derating Chart May 2026

| Ambient Temp (°C) | 90°C Wire (THHN) | 75°C Wire (THW) | 60°C Wire (TW) | |-------------------|------------------|-----------------|----------------| | 21-25 | 1.00 (100%) | 1.00 | 1.00 | | 26-30 | 0.96 (96%) | 0.96 | 0.95 | | 31-35 | 0.91 (91%) | 0.91 | 0.89 | | 36-40 | 0.87 (87%) | 0.87 | 0.82 | | 41-45 | 0.82 (82%) | 0.82 | 0.71 | | 46-50 | 0.76 (76%) | 0.71 | 0.58 |

This guide is written for electricians, engineers, technicians, and hobbyists working with electrical systems, specifically wires, cables, and circuit breakers. 1. What is a Derating Chart? A Derating Chart is a reference table (usually provided by the NEC, IEC, or a manufacturer) that tells you how much to reduce a component's standard current-carrying capacity (ampacity) under non-ideal conditions. derating chart