Keeping currents properly under control Current limitation: The extent of current limitation is described by a factor, normally between 1.25 and 2.0. This value is not exceeded, even in the event of an error. For the power supply, even a hard short circuit therefore has the same eff ect as a slight overload, the current is signifi cantly lower than without current limitation and the supply voltage to the system remains unaff ected. Without current limitation: With a circuit breaker without current limitation, the supply voltage can drop out in the event of an error, which means that all the connected devices would fail as well. This means that, in the event of an error, the installed electronics and the integrated fi rmware must react quickly and intelligently. Although short circuit must be detected and shut down quickly, it must still be possible to reliably start a capacitive load. Intelligent, individual, and intuitive The advantages of electronic circuit breakers Intelligent software is the core of an electronic circuit breaker. The software diff erentiates between operating currents and harmful currents and rapidly transmits commands to the electronic system. Faults must be detected and shutdown as quickly as possible, whereas inrush currents or normal operating currents should not be shut down. The switching operation is performed via the power transistor. Steps to error detection: • Measurement: to monitor the ongoing situation, all electrical variables are measured continuously. • Analysis: the measured values are analyzed in order to determine a course of action. • Classifi cation: the currents are evaluated and classifi ed. • Protect and switch: depending on the class of the analyzed current, the consumer is started or shut down. The rest of the system remains in operation and unaff ected. • Signaling: the operating states of all circuits are transmitted continuously to the system operator. If an event occurs, it is detected immediately and reported. The correct setting To be able to determine the correct nominal current value for a device circuit breaker, you should know the consumer(s). However, the actual current often deviates from the manufacturer's information. In a consumer group, these errors accumulate, which means that the total current deviates even more from the calculated value. Here, adjustable device circuit breakers off er considerable advantages, and therefore a high degree of fl exibility. Firstly, the set value should not be much higher than the fl owing current value. The necessary starting current of a consumer can, however, infl uence the necessary set value. In this case, set the lowest value at which smooth operation can be assured. Adjustable circuit breakers: The intelligent software in the electronic circuit breakers allows the nominal current to be set individually. This means you can maintain the highest level of fl exibility throughout. It is not always possible to determine the correct current value right at the start of a project. Adjustability is therefore a useful function, because the fi nal current value can then be determined during commissioning. You can provide optimal protection for every consumer, tailored precisely to the application. This adjustability also provides you with the option of covering several applications with one device. This not only saves you inventory costs, it also makes selecting the correct circuit breaker much easier. Circuit breakers with fi xed values: For many, circuit breakers provide a high degree of safety if the current value is not adjustable. In this case, nothing can be adjusted in the system, and all of the settings carried out by the installer remain unchanged. The current values must, however, be determined during confi guration. If a value is unsuitable, the entire circuit breaker or protective plug must be replaced. Calculating the cable length In order that the protective device shuts down safely in the event of a short circuit or overload current, the maximum usable cable length should be calculated to be on the safe side. The following data is necessary: • Rmax Maximum total resistance • U Nominal voltage • ICB Rated current CB • xI Tripping factor according to current characteristic curve/multiple of the nominal current • RLmax Maximum cable resistance • RCB1A Internal resistance CB 1 A • Lmax Maximum cable length • A Conductor cross section • ρ Specifi c cable resistance Rho, (Cu 0.01786) Values for sample calculation: • U = 24 V DC • xI = 15 (from the M1 characteristic curve) • ICB = 1 A • RCB1A = 1.1 • ρ • A = 0.01786 (copper) = 1.5 mm2 (assumed) 1. Total circuit resistance: 2. Maximum cable resistance: 3. Maximum cable length: Calculation in three steps PHOENIX CONTACT 7