Design chain, learn how to calculate!

How to calculate electrical project? In a step-by-step electrical project, it is necessary to calculate the design current and the corrected design current, either for a residential or industrial electrical project. Calculation of electrical design is very important for dimensioning cables and protection devices such as the circuit breaker, which is the general switch for the circuits.

The reading of the electrical project involves the analysis of project calculations and the electrical project calculation memorial. It is important to know what is the design current, how to calculate the design current and see examples of design current calculation.

Every time you are going to carry out an electrical project or read about an electrical project you will encounter the project current. Knowing the importance of the design chain The World of Electrical explains what is the design chain and how to calculate the design chain step by step. Come on!

Learn how to calculate project current.

What is design chain? Which formula of the project chain?

The design current is the current that will be calculated and used in a project, this current is used to dimension both cables and protection devices. We can say that it is also the maximum current that the circuit is capable of supporting.

The design current is calculated using the formula shown in the image below.

Generic formula used to calculate project current.

When the power factor is not informed, it is possible to use the tables of typical power factors such as the one shown in the image below:

Table of typical power factors.

Regarding the performance, we should always consider the value 1 when it is not informed by the device. With respect to the number of phases, we will use for circuits with scheme F + N or F + F the value 1, for circuits with scheme 3F + N the value 3 and for circuits with scheme 3F the value is root of 3.

Design current formulas for each circuit.

Regarding the voltage, we will use for phase F + N or 3F + N circuits the phase voltage value. And for circuits with F + F and 3F scheme we will use the line voltage value.

Current design formula for phase voltages and line voltage.

Calculating the project current! Example

Let’s think about the example of an outlet circuit that is a terminal circuit, that is, that leaves the QDC and ends at the outlet points. In our example, circuit 3 has 3 650 W sockets and 2 100 W sockets. In addition, we can also define that both 650 Watt sockets and 100 Watt sockets have a power factor equal to 0.9 and an efficiency equal to 1.

For the 650 Watts sockets we have the following calculation: Design current is equal to 650 Watts of power DIVIDED by 1, because the system informed is Phase and neutral, TIMES 127v which is the phase voltage, TIMES 0.9 which is the reported power factor, TIMES 1 which is the reported yield. Performing the multiplication at the bottom we can see the design current is equal to 650 Watts DIVIDED by 114.3 Volts we have 5.69 Amps.

Result of the project current for 650W.

For the 100 Watts sockets we have the following calculation: Design current is equal to 100 Watts of power DIVIDED by 1, as the system informed is Phase and neutral, TIMES 127v which is the phase voltage, TIMES 0.9 which is the reported power factor, TIMES 1 which is the reported yield. Performing the multiplication at the bottom we can see that the design current is equal to 100 Watts. Dividing by 114.3 volts we have 0.875 Amps.

Result of the design current for the 100W circuit.

Then the total design current will be the sum of the currents for each outlet.

In our example we have 3 650 Watt sockets, that is, the total current of the project will be 3 TIMES 5.69 Amps, + 2 TIMES 0.875 Amps, which is the 100 Watt sockets. Doing the multiplications, the total design current for this example is 17.07 amps, + 1.75 amps, totaling 18.82 amps.

Total design current, adding 100W and 650W sockets.

This value of 18.82 Amps should be used for dimensioning both the cables and the circuit breaker for this circuit.

Another example to calculate the design current is this circuit of a three-phase socket installed on the floor, with a power of 12,500 Watts.

For this 12,500 Watts socket we have the following calculation: Design current is equal to 12,500 Watts of power DIVIDED by 3, because the system informed is three-phase, TIMES 127v which is the phase voltage, TIMES 0.8 which is the informed power, TIMES 1 which is the yield that is also informed. Performing the multiplication at the bottom we can see that the design current is equal to 12,500 Watts DIVIDED by 304.8 Volts, totaling 41.01 Amps.

Result for 12500W design current.

To perform any current calculation for electrical projects, this formula should be used. See that there is nothing complicated in mathematics, just multiplication and division that you do with the aid of a calculator.

The video below the Mundo da Elétrica channel talks about project current and teaches step by step how to calculate the project current, in addition to highlighting important points on the subject.

Importance of the design chain.

Perhaps the greatest difficulty is to understand the concepts, and for that the World of Electrical is here to help. The design current is what ensures that an electrical project will be installed or carried out safely, ensuring that cables and circuit breakers do not overheat or have faults that can lead to electrical accidents.

In Brazil there are several cases of electrical accidents and many of them evolve into fires, these occur because poorly executed projects end up overheating or causing short circuits that can generate sparks.

The safety of users of an electrical installation must be taken seriously and this must occur both in the design phase and in the execution and maintenance phase.