How To Choose A, B, C, And D Types of Miniature Circuit Breakers? (4)
B. Three-phase is generally divided into three types of circuit breakers, namely 3P, 3PN, and 4P
(1) Difference:
3P: There are only 3 wirings, which are only used for pure three-phase electrical equipment. It will trip when the phase-to-ground or phase-to-phase short circuit occurs, and there can be no single-phase load. The N-line return circuit breaker operates as a leakage current.
3PN: 4 wires L1L2L3N can use three-phase power or single-phase power behind the transformer coil, no matter whether the three-phase load is balanced or not, the leakage switch will not act. It only acts when there is leakage, that is to say, when a single phase is grounded or short-circuited between phases。
4P: The 4 wirings L1L2L3 all pass through the transformer coil. The usage method is the same as that of 3PN. The difference is that 4P breaks the N line, and 3P keeps the N line.
(2) Division:
Four-pole circuit breakers are divided into four types: A, B, C, and D:
a: No over-current release is installed on the N pole, and the N pole is always connected, and is not combined with other three poles.
b: No overcurrent release is installed on the N pole, and the N pole is combined with the other three poles.
c: An overcurrent release is installed on the N pole, and the N pole is combined with the other three poles.
d: An overcurrent release is installed on the N-pole, and the N-pole is always connected, and is not combined with other three poles.
(3) Application：
a. In the case of using four poles, be sure to indicate which product is used, because both are four poles, but whether an overcurrent release is installed on the N line has different functions and purposes.
An overcurrent release is installed on the N line, which can be used in the line where the single-phase load is dominated by the three-phase four-wire distribution, or in the nonlinear load that generates a large number of harmonics, such as gas discharge lamps. SCR dimming, speed control circuits, or other occasions with special requirements. For general equipment circuits, a circuit breaker without an overcurrent release on the N line can be selected.
b. In fact, although the two types of A and D are called four-pole circuit breakers, their N poles are always connected, and they are not combined with the other three poles. Therefore, this type of MCCB is commonly known as "false quadrupole", which is 3P+N, which has no essential difference from the three-pole MCCB. The only thing it is more useful than a three-pole is in a complete cabinet, where the wiring may be easier to get in and out of.
Therefore, this type of circuit breaker can only be applied to three-phase loads but a small amount of single-phase loads. If the wrong choice is made, it will not only fail to protect, but will cause major problems. This is the most chaotic problem in current design and use, and should be paid attention to.
