Cable Rating Calculation May 2026

When in doubt, go one size larger. The cost of copper today is trivial compared to the cost of a trench re-dig, a fire investigation, or a day of factory downtime.

Always add a safety margin. For continuous loads (running >3 hours), multiply the load current by 1.25 (125%). Step 2: The "Big Three" Correction Factors Cable tables (like NEC Table 310.16 or IEC 60364-5-52) assume perfect conditions: 30°C air, free airflow, and pure copper. Your site isn't perfect. You must derate. cable rating calculation

( VD = \sqrt{3} \times 150 \times 16.4 \times 0.0045 ) ( VD = 19.2 \text{ Volts} ) When in doubt, go one size larger