As for MCBs, 1P+N, 1P, 2P are generally used as the control for single-phase electrical appliances.
(1) Differences: 1P—Single-pole circuit breaker: Has thermal trip function, can only control live wire (phase wire), module size 18mm; 1P+N—Single-pole + N circuit breaker: Controls both live and neutral wires, but only the live wire has the thermal trip function; module size is also 18mm; 2P—Single-phase 2-pole circuit breaker: Controls both live and neutral wires, and both have thermal trip functions, module size is 2*18mm = 36mm;
(2) Applications:
- To reduce costs, a 1P can be used, but the upstream circuit breaker must have a leakage trip function, and to prevent accidents due to confusion between live and neutral wires during maintenance, the upstream power supply must be cut off;
- To avoid the problem with 1 during maintenance, a 1P+N can be used;
- The reason to use a 2P: For the same 18mm module size circuit breaker housing, the internal installation of a 1P and 1P+N is different. The former’s “ultimate breaking capacity” under a short-circuit accident is definitely higher than the latter, as space is a crucial factor affecting the breaking capacity. Thus, for essential circuits that require frequent maintenance and operation and are prone to faults, it’s best to use a 2P (although it’s more costly);
- Using a 1P requires that the lighting distribution box must have a leakage trip function, at least the incoming line (or the one above the outgoing line) should use a residual current circuit breaker;
- Ordinary socket circuits can fully utilize a 1P+N, but it won’t work if you want to add leakage protection, as a 1P+N circuit breaker cannot be assembled with leakage protection accessories and other electrical accessories.
Three-phase circuits generally use three types of circuit breakers, namely 3P, 3PN, and 4P.
3P: With three terminals, it is used for purely three-phase electrical appliances. It will trip in the event of a short circuit either between phases or to the ground. It can’t handle single-phase loads; otherwise, if there is a load on any phase to neutral wire, the returning current in the neutral wire will act as a leakage current in the breaker.
3PN: With four terminals (L1L2L3N) all passing through the transformer coil, it can handle both three-phase and single-phase electricity. The leakage circuit breaker does not operate regardless of whether the three-phase load is balanced; it only operates when there is leakage, that is, during a single-phase grounding or phase-to-phase short circuit.
4P: With four terminals (L1L2L3), it operates like the 3PN, with the only difference being that the 4P interrupts the neutral wire, while the 3P does not.
(2) Division:
Four-pole circuit breakers are divided into A, B, C, and D types:
A: The neutral (N) pole does not install an overcurrent trip device and is always on, not joining the other three poles in operation.
B: The neutral (N) pole does not install an overcurrent trip device but operates together with the other three poles.
C: The neutral (N) pole installs an overcurrent trip device and operates together with the other three poles.
D: The neutral (N) pole installs an overcurrent trip device but is always on, not joining the other three poles in operation.
(3) Applications:
In the case of using four-pole devices, it is necessary to specify which type is being selected from the product range. Even though they are all four-pole devices, the function and purpose are different depending on whether an overcurrent trip device is installed on the neutral wire.
A circuit breaker with an overcurrent trip device installed on the neutral wire can be used in lines where the single-phase load is dominant in three-phase four-wire power distribution, or in non-linear loads generating a large amount of harmonics such as gas discharge lamps, silicon-controlled rectifier dimming/speed control circuits, or other cases with special requirements. General equipment circuits can use circuit breakers that do not install an overcurrent trip device on the neutral wire.
In reality, although types A and D are called four-pole circuit breakers, their neutral pole is always on and does not operate together with the other three poles. Hence, these types of MCCBs are commonly known as “pseudo four-pole” or 3P+N and have no essential difference from three-pole MCCBs. The only advantage of these over the three-pole types is that they may provide convenience for line entry and exit in switchgear assemblies.
Therefore, these types of circuit breakers can only be suitable for applications in three-phase load scenarios but also have a small amount of single-phase load (such as packaged systems using 220V control power).
If the wrong type is selected, not only will it not provide protection, but it could also lead to significant problems. This is currently one of the most chaotic issues in design and usage and should receive attention.