How to determine the distribution level

The distribution level refers to the number of times a power supply circuit is divided into several sub-circuits through distribution devices; the number of such divisions determines the level of distribution. For a power distribution apparatus, the main incoming switch and the branch outgoing switches together constitute the first level of power distribution; this is independent of whether the main incoming switch is a circuit breaker or a disconnect switch, and the level of power distribution does not change just because a circuit breaker is used as the main incoming switch. The protection level is determined by the number of upper and lower levels of the protection switches; it is related to yet distinct from the distribution level. For the number of distribution levels at the same voltage level, there should not be more than two levels for high voltage; generally, there should not be more than three levels for low voltage. For third-level loads, there should not be more than four levels ； The protection levels can reach five or even six, and under normal circumstances, coordination between different protection levels is necessary. It should be noted that when both the main incoming circuit breaker (A) of the lower-level power distribution unit and the outgoing circuit breaker (B) corresponding to it in the immediately upper-level power distribution unit are circuit breakers, they should be considered as part of the same protection level. (In this case, the main incoming circuit breaker at the lower level should have an isolation function, or an isolating switch should be installed in front of it.) That is, in the event of a fault, whether it is the A circuit breaker or the B circuit breaker that trips, the resulting effect (the area affected by power outage) remains the same; there is no issue of protection coordination (i.e., selectivity) nor any problem of so-called \"cross-level tripping.\" It is difficult to define this concept clearly, so it is easier to illustrate it with examples, using the power distribution in residential buildings as an example. 1. The low-voltage output of the transformer, at 380V (400V), enters the low-voltage distribution cabinet, where the electrical power is distributed in multiple circuits; this constitutes the first level of power distribution ； 2. The power from the previous outlet is sent to the distribution boxes (or cabinets) on each floor, where it is further divided into multiple circuits. These distribution boxes carry out the second level of power distribution, which constitutes level 2 distribution ； 3. The electricity after secondary distribution may undergo a third distribution via regional distribution boxes; these regional distribution boxes represent the third level of power distribution. The number of distribution levels should generally not be too high, as too many levels reduce the reliability of the system; however, it should not be too low either, as this would result in a wide impact from failures. In residential buildings, 3 levels of distribution are commonly used, while larger facilities may employ 4 levels.