Ohm's law and electrical engineering in everyday life

Material knowledge Ohm's law electrical calculation and voltage drop calculation are already on the schedule in the basic course's second part. This is no accident — these basic formulas you use for the rest of your career every time you need to assess whether a cable is correctly dimensioned or why a section behaves differently than expected.

§Ohms lov: U = R × I

Ohm's law describes the fundamental relationship between voltage (U, measured in volts), resistance (R, measured in ohms) and current strength (I, measured in amperes). If you know two of the three quantities, you can always calculate the third. It is the most basic formula in electrical engineering — and the one that everything else is built upon.

§Effekt: P = U × I

Power (P), measured in watts, tells how much energy is converted per second. By combining the power formula with Ohm's law you can calculate how much heat a cable generates under a given load which is crucial for choosing the right cross-section and avoiding overheating.

• 01Sizing of cable cross-section based on expected load
• 02Calculation of heat development and loss in wires
• 03Understanding why fuses are set to specific ampere values
• 04Assessment of whether a system is over or underloaded

§Voltage drop – why it matters over long distances

The longer a cable is, the more resistance the current encounters along the way, and the more voltage drops from one end to the other. If the voltage drop is too large, equipment at the end of the line cannot get the voltage it is designed for. That's why voltage drop calculation is a fixed part of the curriculum – it's about ensuring that the customer at the end of a long cable run still gets a voltage within acceptable limits.

§A simple calculation example

Forestil dig en kabelstrækning med en samlet modstand på 2 ohm, der belastes med en strøm på 10 ampere. Ifølge Ohms lov (U = R × I) giver det et spændingsfald på 20 volt hen over strækningen — 2 ohm gange 10 ampere. Er udgangsspændingen for eksempel 230 volt, ender kunden for enden af strækningen altså med at få omkring 210 volt. Er det inden for de tilladte grænser, er alt i orden; er faldet for stort, skal der enten bruges et tykkere kabel med lavere modstand, eller strækningen skal forkortes eller forstærkes med en ekstra transformerstation.

This type of calculation is not academic exercise — it is something you use in practice when new sections need to be designed or when a customer at the end of a long cable complains about unstable equipment. Being able to calculate whether the cause is voltage drop or something else saves time and makes troubleshooting targeted from the start.

§Why it does not stop at the schoolboard

Many students find that electrical theory on paper feels far from the practical work out in the field. But in practice, you use these formulas every time you need to assess whether a fuse cabinet is dimensioned correctly for the load, whether a customer's complaint about unstable voltage is justified, or whether a new connection can handle the extra consumption a heat pump or an EV charging station adds. The basic formulas from the basic course are, in other words, the tool you continually return to, regardless of how far you get in your career.

It is precisely for this reason that it is worth spending time understanding the formulas properly already while you are in the basic course instead of just learning them by heart for a test. A student who understands the connection between voltage current resistance and power will later in the main course have much easier time understanding why a system is dimensioned as it is — and will quickly be able to see through what is wrong the day something does not behave as it should.

“Ohm's law is short — but it underlies almost every professional assessment you make as a supply operator.”