You need at least 7.3 mm² . The nearest standard size is 10 mm² (since 6 mm² would be too small). Step 4: Adjust for Temperature and Grouping The formula above assumes ideal conditions. If cables run through hot attics or are bundled together, use these derating factors (from NEC/CEC tables):
A 2000W water heater on 230V. ( I = 2000 / 230 = 8.7 \text Amps ) Step 2: Determine the Round-Trip Cable Length Many forget this. If your device is 20 meters from the source, the actual electrical path is 40 meters (go and return).
But don't worry. Calculating the correct cable size is straightforward once you understand the four key factors: calculate cable size
Now calculate cable size for , not 5A. Quick Reference: Common Cable Sizes & Current Ratings (Copper, 30°C) Use this as a starting point only—always verify with local codes.
Let’s break it down. Electricity flowing through a cable generates heat. The smaller the cable, the more resistance and heat it produces. The goal is to choose a cable large enough to carry the required current without exceeding its temperature rating. You need at least 7
| Condition | Derating Factor | | :--- | :--- | | Ambient 30-40°C (normal) | 1.00 | | Ambient 40-50°C (hot attic) | 0.87 | | 3-6 cables bundled | 0.80 | | 7-9 cables bundled | 0.70 |
Got a specific project in mind? Drop the details below, and I’ll help you calculate it! Disclaimer: This guide is for educational purposes. Electrical work can be dangerous and fatal if done incorrectly. Always comply with local codes and regulations, and hire a qualified electrician for permanent installations. If cables run through hot attics or are
Choosing the wrong cable size isn't just an inconvenience—it’s a fire hazard. Undersized cables overheat, melt insulation, and can cause voltage drops that damage your equipment.