Electricity basics

Learn voltage, current and power, and recognize AC (alternating current) vs DC (direct current). Use an interactive calculator to see the relationships immediately.

This page gives you an overview of the core basics of electricity.

Power, current and voltage (U, I, P)

In electrical installations, three variables keep coming back:

• Voltage (U) in volt (V)
• Current (I) in ampère (A)
• Power (P) in watt (W)

In the day-to-day installation world, the relationship between these variables often shows up as:

• P = I · U

Meaning: if you change Power (and Voltage stays what it is), the Current changes too, and vice versa.

In the app, you see that logic whenever you need to understand: *which breaker rating still makes sense for the cable and the load?*

Ohm’s law (electrical basics)

Ohm’s law is usually linked with resistance (R): *U = R · I*. In many practical explanations, though, you keep reusing the same “two give the third” relations between U, I and P.

The calculator below lets you play with the formulas between these variables.

AC and DC (alternating vs direct)

AC (alternating current) changes polarity and amplitude over time. It’s the standard for the grid and most household installations.

DC (direct current) flows in one direction (no regular time-varying polarity). You see DC in batteries, the DC side of PV inverters, and in certain charging setups.

The practical difference mainly comes from the components you use (inverters, protections) and how the load is fed.

Energy and kilowatt-hour (kWh)

People often mix up power (W or kW) and energy (Wh or kWh):

• Power = how fast energy is being used or delivered right now.
• Energy = how much has been used or delivered over time.

Useful rule of thumb:

• 1 kW during 1 hour = 1 kWh
• 2 kW during 30 minutes = 1 kWh

Your electricity bill and digital meter primarily track kWh, not instantaneous power.

Phase, neutral and earth

In a typical domestic installation you have a phase conductor and a neutral conductor:

• Phase (L) carries alternating voltage relative to neutral.
• Neutral (N) is the return path and ideally stays close to earth potential.

Many residential circuits operate as L + N (plus protective earth where required).

Three-phase (3~)

With three-phase, you have three phase conductors (L1, L2, L3), shifted in phase relative to each other. That lets you:

• distribute higher power with lower current per phase,
• feed heavier loads more stably (e.g. EV chargers, motors, some heat pumps).

Depending on the grid type, you’ll work with:

• 3 x 230 V
• or 3 x 400 V + N

In diagrams and calculations, it is crucial to show clearly which phase(s) each circuit or device is connected to.

Use this page as an entry point:

• first understand the variables,
• then go into resistance/impedance and real use cases.