The most important electrical components in the distribution box include the isolation switch, which is usually used as the main incoming switch for safety isolation function. Only when the protection characteristics meet the requirements of the protected circuit and the selectivity of the upper and lower protection circuits and the installation characteristics of the components are determined, can reliable and safe protection function be played.The most common problem is before and after the level of protection characteristics are not coordinated, circuit breaker characteristics are not appropriate, leakage circuit breaker selection is not appropriate, there are unqualified components and so on.These problems are caused on the one hand because designers can not understand the performance indicators of various electrical components correctly, on the other hand because of the non-standard procurement construction.
Distribution box at home will often see air conditioning outlet loop distribution with other power outlet, outlet and kitchen toilet socket into a loop, apparently did not meet the requirements of the specification, will undoubtedly accelerate the aging line, increase the risk of electrical fires in the practical application of the most common distribution box is embedded, has the characteristics of beautiful and not occupy a space.After installation, the box is closed and not easy to heat dissipation. Due to modular installation of components in the distribution box, the electrical components are closely installed side by side, which is obviously different from the normal use conditions.The most important electrical components used in the distribution box are small circuit breakers. Small circuit breakers generate heat through current when working normally, and the mutual influence of heat causes heat dissipation difficulties, which can not meet the normal use conditions of electrical components.
Therefore, it is very important to determine the rated current of the circuit breaker. The circuit breaker should be used according to the capacity reduction provisions provided by the manufacturer's operating manual, and can be determined by test when conditions are available.Distribution in each branch circuit breaker should choose how much rated current is appropriate, modern lighting device both in home and other applications, are all made of pure resistance of lamps and lanterns is very few, general with energy-saving lamps "fluorescent lamps and lanterns and air conditioner etc contain motor load is the most common, because this kind of load containing perceptual belongs to nonlinear load, the current waveform becomes extremely irregular,And ordinary ammeter can not measure harmonic current, obviously simply according to the calculation of current size to choose the rated current of circuit breaker is not appropriate, so according to the composition of the actual load for appropriate consideration.For example, for some with a high power motor load is applicable to consider the choice of motor protection of the circuit breaker.This explains why it is clearly according to the calculation of current and consider the allowance of the circuit breaker is still frequently overload action, the terminal temperature has been very high reasons.
In practice, it is common to see that in order to save cost, some manufacturers do not select the cross-sectional area of the wire according to the standard service conditions, which will lead to long-term over-load operation of the wire, and accelerate the aging of the wire will cause the danger of fire.The installation mode and internal structure characteristics of the distribution box determine that there are obvious differences between the internal conductor and the normal and ideal operating conditions, so the choice of the conductor cross-sectional area is a key factor.Some distribution box according to the current of circuit breaker after reducing capacity of cross-sectional area of choice is wrong, should be stipulated in the circuit breaker operating instructions or nominal rated current according to the circuit breaker to select the sectional area of the wire circuit breaker fever and influence each other between conductor, the airtight not easy to heat the temperature in the cabinet, is no longer a conductor is normal use conditions, if the cross-sectional area is not will affect the correct choiceThe protective characteristics of circuit breakers affect the service life of wires.The rated current of the circuit breaker shall be selected according to the calculated current and service conditions, and the voltage drop, installation mode, ambient temperature and load composition shall be taken into account according to the calculated current.
