Choosing between a 1P and a 2P MCB for a single-phase circuit looks like a simple decision, and in many boards it is. The two devices are not interchangeable in every installation: the right choice depends on the earthing system, on whether the neutral has to be isolated for maintenance, and on what your local wiring code requires for the circuit in question.
The short answer: a 1P MCB protects and switches only the line conductor. A 2P MCB protects and switches both line and neutral. The 1P+N device that sits between them switches the neutral but only protects the line. If the neutral must be broken for safe isolation, 2P or 1P+N both do that job. If the neutral also has to be protected against overcurrent, only 2P does it.
The number in front of the P is the number of poles, but “pole” is used loosely in catalogues, and that is where most of the confusion starts. Three figures matter, and they are not always the same:
| Perangkat | Modules (18 mm) | Conductors switched | Conductors protected | Typical use |
|---|---|---|---|---|
| 1P | 1 | Line | Line | Single-phase final circuits where the neutral stays solid |
| 1P+N | 2 | Line + neutral | Line only | Circuits that need neutral isolation, with a load that does not need neutral protection |
| 2P | 2 | Line + neutral | Line + neutral | TT systems, generator and temporary supplies, polarity that cannot be guaranteed |
| 3P | 3 | Three lines | Three lines | Three-phase load without neutral |
| 4P | 4 | Three lines + neutral | All four | Three-phase plus neutral, or installations that require all-pole isolation |
The important row is the second one. A 1P+N takes the same rail space as a 2P and looks almost identical in a photograph, but its neutral pole is a switch contact with no overcurrent element behind it.
In a TN-S or TN-C-S installation with a solidly earthed neutral, the neutral sits at earth potential in normal operation. Isolating the line removes the supply from the circuit, which is what a single-phase final circuit usually needs. That is why 1P devices dominate domestic boards in many markets: they are cheaper, take half the rail space, and can share a comb busbar along the whole row.
Two conditions have to hold before you can rely on that. First, the neutral must not be switched or interrupted anywhere downstream in a way that could leave it floating. Second, your local wiring code must accept single-pole isolation for that circuit type. Both are installation-specific, and neither can be assumed from a datasheet.
TT earthing. In a TT system the fault current returns through the general mass of earth, not through a metallic path back to the transformer. During a fault the neutral can rise above earth potential, and if only the line is broken, the circuit is not actually dead. Double-pole isolation is the normal requirement here, and a 30 mA RCD is present anyway for fault protection.
Supplies where polarity is not guaranteed. Plugs that can be inserted either way, shore power connections, generator feeds, and temporary distribution boards all fall into this group. If line and neutral can be swapped upstream, a device that protects only one pole is protecting the wrong conductor half the time.
Neutral used as a current-carrying conductor. Where the neutral carries harmonic current or is shared between circuits, it can be overloaded independently of the line. Only a device with a protective element in the neutral pole will see that.
Codes that require all-pole isolation. Several national codes require both poles to be isolated for certain equipment, certain locations, or certain circuit types. This is the one item you cannot decide from first principles; check the code that applies to the project.
Because a 1P+N breaks the neutral, it satisfies the isolation requirement in many installations, and it is often the standard choice for single-phase final circuits in Europe and Australia. It does not, however, protect the neutral. That difference matters in three situations:
If your reason for choosing 2P is neutral isolation alone, 1P+N is a legitimate and cheaper answer. If your reason is neutral protection or uncertain polarity, it is not.
This is a frequent and expensive misunderstanding. A 2P 16 A breaker carries 16 A per pole, not 32 A in total. The two poles are mechanically linked and share one trip mechanism, so the rating applies to each pole individually.
In a single-phase circuit the neutral current equals the line current, apart from harmonic content, so both poles see the same value. Buying a 2P 32 A device to feed a 32 A load does not create margin; it simply protects a 32 A circuit at 32 A, which may be above the cable ampacity. The rating is still selected from the load current, the cable, and the coordination with upstream protection.
On an 18 mm module rail, moving a board from 1P to 2P devices halves the number of circuits that fit. A 24-module enclosure that holds 24 single-pole circuits holds 12 double-pole ones, before the main switch, RCDs and any SPD are counted.
That has a knock-on effect on spare capacity. If you are planning a board with double-pole devices, reserve the spare ways in modules rather than in circuits, and check the count after the main switch and RCDs are subtracted. The arithmetic for that is set out in our guide to distribution box layout and spare module space.
If all four answers are no, a 1P device is adequate and gives you twice the circuits per rail. For three-phase boards the same logic applies with 3P and 4P, and the neutral question becomes more involved; that is covered in 3P vs 4P breakers for three-phase distribution.
It is safer in the specific sense that it isolates both conductors and protects the neutral. Whether you need that depends on the earthing system and the code, not on a general safety ranking. In a TN-S domestic board, a 1P device with RCD protection is a normal and compliant solution.
No. The two poles are mechanically linked and share a common trip, so a fault on either circuit opens both. The device is also rated as one circuit, not two.
No. The neutral pole is switched but has no overcurrent element. It provides isolation, not protection.
Voltage alone does not decide it. A 230 V circuit in a TN system with a solid neutral is commonly protected by a 1P device. The deciding factors are the earthing system, polarity, and local requirements.
The same logic applies. A 1P+N RCBO switches both conductors and provides residual current protection, but its overcurrent element is in the line pole only. It is widely used for single-phase final circuits and is not equivalent to a 2P RCBO.
If you are specifying boards for a project, matching the device type to the earthing system before ordering is cheaper than changing it after the first inspection. Our AC MCB range lists single-pole, double-pole and 1P+N versions with their module widths, and the circuit breaker category covers the wider selection including RCBO and RCCB devices.
