Link to purchase the Electrical Calculations Spreadsheet: https://hotm.art/ytd-planilha-calculo... Link to purchase the Load Panel Calculation Spreadsheet: https://hotm.art/ytd-planilha-quadro-... Link to purchase the Electrical Plant Sizing Spreadsheet: https://hotm.art/ytd-planilha-plantas... __________________________________________________ If you like the Eletricity channel and want to contribute to the generation of quality content, then access one of the options below: PIX KEY ???? [email protected] QR CODE ???? https://bit.ly/doacao-pix __________________________________________________ Receive Eletricity content straight to your email! Register using the link below: ???? https://bit.ly/cadastro-eletricity __________________________________________________ ???? Check out our content ???? ???? https://linktr.ee/Eletricity __________________________________________________ Can I completely ignore circuit breaker curves? Is following just the basic rules with the most common types of curves enough? You've probably already seen videos about circuit breaker curves, including here on the channel. Generally, in these videos, circuit breakers are classified as follows in relation to the curves. Curve B: A curve B circuit breaker has a breaking current between 3 and 5 times the nominal current and is normally used for resistive loads, which have low starting current. Curve C: A curve C circuit breaker has a breaking current between 5 and 10 times the nominal current and is used in circuits where the current demand for starting equipment is medium, normally inductive loads, such as motors, command and control systems, lighting circuits in general. Curve D: A curve D circuit breaker has a breaking current between 10 and 20 times the nominal current and is used in circuits where the starting current is very high, such as in large motors and large transformers. So far so good, it is a way to give some direction to the circuit breakers. If we analyze curves B, C and D we clearly notice that the indication of a curve B for resistive loads is related to the fact that we have low starting currents. It is like a shower or an electric oven. As in these cases, any variation in voltage results in a proportional variation in current, that is, the higher the voltage, the higher the current. If I have a shower with a current of 25A, using a curve B circuit breaker of 32A, the instantaneous actuation would be at 96A. I can't think of a reason why my shower's circuit breaker wouldn't actuate under these conditions. In the case of curve C for loads with high starting currents, it also makes perfect sense. For example, if I have a motor with a starting current 6 times higher than the nominal current, it is very likely that a circuit breaker with curve B will trip instantly, preventing it from working, which would not happen with curve C. For curve D, the reasoning is almost the same as for curve C. If my load has a starting current 12 times higher than the nominal current and I do not want the circuit breaker to trip when starting, I need to use curve D, because in this case a curve C or B would certainly trip. Okay, is this alone enough to determine the curve of a circuit breaker? Is there another factor to be considered? The answer is yes. It is necessary to analyze the short-circuit current. The electrical conductors that we know have, in addition to electrical resistance, a portion of inductive reactance. The interaction between these two components results in what we know as impedance, which is given in ohms. To put it very simply, the short circuit occurs when I have no load, so I have the circuit voltage across a series of impedances. They are: Impedance of the cables from my circuit to the QDC, Impedance of the cables from my QCD to my meter, Impedance of the cables from my meter to my Transformer, The short-circuit current would be obtained by dividing the circuit voltage by these impedances and the longer the circuit, the greater the impedance, consequently, the lower the short-circuit currents. In short, a short in your input standard has greater intensity than a short in a circuit in your home outlet. If I have very low short-circuit currents and use a curve C circuit breaker, it is possible that the longer operating time will damage the conductors in my circuit. Very well, everyone, we have shown that the short-circuit current makes a lot of difference and is extremely important in determining the circuit breaker curve. So we can add to curve B the use in long circuits with low-intensity short-circuit currents. Until next time. ???? Stay tuned for #electricity ????