Basic Rules of Electrical Calculations

There is no doubt that everyone on Earth has at least once considered building a house. Electricity is an integral part of modern life, so a house must be electrified. While laying the foundation and building walls may seem straightforward, calculating the electrical wiring raises many more questions.

Electricity has no smell, taste, or color, and therein lies its main danger. Therefore, we entrust electrical work to specialists or those who claim to be. It’s not surprising that the homeowner controls every stage of construction, and when it comes to calculating electrical wiring, it’s good to know the basic rules. For example, how do you correctly determine the length of wires? Does the thickness and color of wires matter? Which wires should you choose, aluminum or copper? If you’ve ever pondered at least one of these questions, this article is what you need.

Let’s start with the basics: electric current in conductors is the flow of charged particles. Current can be likened to water flow through a pipe: for a powerful water flow, you need a thicker pipe. Accordingly, one of the main points of electrical wiring calculation is finding the current based on power and voltage. How do you find the total power of electrical load? You need to sum up the powers of all appliances that will operate in the house, apartment, or building.

For example, by summing the powers of a microwave (700 W), refrigerator (1000 W), vacuum cleaner (2200 W), induction cooker (7200 W), and water heater (2000 W), we get a total power of 13,100 W. Power, measured in watts, can easily be converted into current by dividing its value by 220. In our case, it amounts to 60 amperes – this is the current that would flow through the main cable if all electrical appliances in the house were turned on simultaneously.

Having understood the current, we move on to selecting the cross-sectional area of the conductors. The cross-sectional area of the cable’s core is chosen based on the current using special tables.

Copper wires are more expensive than aluminum ones, but they are more reliable and durable at connection points, such as automatic switches. Wires and cables with aluminum cores of less than 16 mm² in cross-sectional area are not allowed to be used during installation. If there is a need to connect copper cores with aluminum ones, it is necessary to use terminal blocks – specialized electrical devices designed for reliable and safe contact between conductors made of different metals.

During electrical installation, the use of twist-on wire connectors is prohibited. Connecting copper and aluminum wires is particularly dangerous. These metals chemically react with each other, leading to local increases in electrical resistance, intensive heat generation, and further degradation of conductors.

Let’s return to our calculations. Knowing the approximate current that will flow through the main cable, you can choose an automatic switch. On the market, nominal current values, as well as conductor sizes, are standardized, so in our example, a 63 A circuit breaker would be suitable.

So, we have just completed the main part of the calculation, selecting the cross-section of the main cable and the nominal current of the circuit breaker. The same principles apply to calculating conductors in individual rooms or for specific types of loads, such as lighting. Circuit breakers protecting specific groups of consumers or rooms should be appropriately labeled.

The color of the cable sheath does not affect current flow, but electricians installing the wiring will follow this scheme: yellow, green, or yellow-green wires are for protective grounding; blue or black are for neutral wires; white or other colors are for phase conductors.

Choosing the length of cables is perhaps the most challenging part of electrical wiring calculation. First, measure the distance from the power source (such as a circuit breaker or junction box) to the consumer (such as a socket). It’s important to know the number and placement of sockets, switches, light fixtures, and ceiling height. Moreover, different types of loads (light fixture, computer socket, kitchen stove) require corresponding conductor sizes. For example, a 1.5 mm² cross-section wire is sufficient for lighting, but not for a stove.

During cable laying, cables will be cut, and unforeseen circumstances may arise, so it is advisable to take a slightly longer length based on work experience and budget. Of course, there are rules like “allow 2-3% extra length for cutting” or even “the length of the wiring numerically equals double the area of the apartment,” but precise figures can only be obtained through accurate measurements. It’s good to remember that an additional 20-30 cm will be needed for each connection point.