Ohm's Law
For those less familiar with the electrical concept of Ohmic resistance, we have written this article.
Ohm's Law (U = I × R) is more than a theoretical formula – it is a fundamental concept for anyone who designs electrical installations, from electricians to safety inspectors. In this blog post, you will discover how to apply Ohm's Law in everyday situations. George Simon Ohm (1789 - 1854) discovered the relationship between Voltage (expressed in Volts) and Current (expressed in Amperes).
1. Circuit Protection
When designing an electrical installation, you need to know what current flows through a circuit. Ohm's Law allows you to calculate this and also determine the required level of protection:
Example: A 230V circuit with a total resistance of 23Ω draws a current of I = 230 ÷ 23 = 10A. This means you need at least a 16A fuse.
2. Determining Cable Thickness
Cables have resistance that generates heat. Cables that are too thin for high currents can overheat and pose a fire hazard.
Practical example: For a 3000W appliance at 230V, you calculate: I = P ÷ U = 3000 ÷ 230 = 13A. According to NEN 1010, you need a minimum of 2.5mm² cable for this.
3. Calculating Voltage Drop
Long cable runs cause voltage drop due to cable resistance. Ohm's Law helps you predict this.
Example: A 50-meter cable with 0.4Ω resistance at 10A current: U = I × R = 10 × 0.4 = 4V voltage drop. At 230V, this is acceptable, but for longer distances, you need to use thicker cables.
4. Troubleshooting and Measurements
With a multimeter and Ohm's Law, you can track down defects:
- Measure voltage and current, calculate resistance
- Compare with the expected value
- Deviations indicate short circuits, interruptions, or poor connections
5. Power Calculations
Combine Ohm's Law with power formulas (P = U × I):
Example: A 2300W heating element at 230V draws I = 2300 ÷ 230 = 10A and has a resistance of R = 230 ÷ 10 = 23Ω.
Conclusion
Ohm's Law is indispensable for performing calculations in electrical engineering. Whether you are designing circuits, troubleshooting faults, or performing NEN 3140 inspections, an understanding of U = I × R is an important basis.