Motor protection circuit breaker with thermal and electromagnetic release with neutral pole N M250 (20A - 25A) 606812

Three-phase motor protection in modular distribution boards

The M250 series motor circuit breakers are electromechanical devices dedicated to protecting electric motors from the effects of overloads and short circuits in three-phase installations. In this specific version equipped with a thermal-magnetic trip unit and an N neutral connection, the device provides full two-level protection of the windings - the thermal unit reacts to long-term overcurrents, while the electromagnetic unit instantaneously trips the circuit in the event of a short circuit.

The thermal trip setting range is 18-25 A, allowing for precise adjustment of the trip threshold to the rated current of the protected motor. Adjustment is performed via a dial with a scale, enabling settings with accuracy down to fractions of an ampere - crucial for motors with critical starting parameters. The electromagnetic trip has a fixed setting in the range of 280-420 A (depending on the source, a value of approximately 350 A is provided, corresponding to a tolerance of ±20%). Thanks to this, the device does not react to momentary current spikes during motor startup but immediately cuts the power during a short circuit.

Construction and components

The housing fits on a DIN TH35 rail - a standard mounting bracket used in modular distribution boards. The device width is 45 mm, which corresponds to 2.5 modules, so it does not take up excessive space in the enclosure. The power supply direction is from the top - typical for most modular circuit breakers, facilitating cable routing.

Connection is implemented via screw terminals supporting wire cross-sections of 1-4 mm². The operating element is a manual lever, which serves both to switch the circuit on and off and to signal the contact state - the installer can see at a glance whether the breaker is closed or open.

The device has an IP3X protection rating - protecting against finger access to live parts and against solid foreign objects >12.5 mm. In standard industrial and workshop environments, this is a sufficient level; for more demanding conditions, it is worth considering an additional enclosure.

Mechanical durability is 100 000 operations, and the maximum switching frequency is 120 cycles/h. This means a lifespan allowing for many years of operation even under intensive manual control.

Operating parameters and application

The breaker operates at a mains voltage of 230-500 V AC at a frequency of 50-60 Hz. The rated operating power for category AC-3 (direct motor starting) is:

• 4.5 kW at 230 V,
• 7.5 kW at 400 V.

Some sources provide a higher maximum power value (11 kW) - the difference likely results from a different interpretation of catalog data or the use of additional cooling accessories. When selecting a breaker for a specific motor, always check its rated current and compare it with the thermal setting range.

The rated short-circuit capacity Icu at 400 V AC is 3 kA - typical for breakers of this class, sufficient in building installations and light industrial applications with fuse links as selective supervisory protection.

The device does not have a phase loss sensitivity function or a built-in auxiliary contact - however, these functions can be added via dedicated side-mounted accessories (e.g., PS M250 auxiliary contacts or undervoltage releases).

Standards and operating conditions

Production is carried out in accordance with the IEC/EN 60947-2 standard, which specifies requirements for low-voltage circuit breakers. The device also meets the IK04 impact resistance classification.

Operating conditions:

• operating temperature: from -5°C to +40°C,
• permissible mounting position: any,
• voltage type: AC.

The housing is halogen-free - important for installations requiring low smoke emission in case of fire (e.g., tunnels, sports halls).

The M250 series offers several functional variants:

• M250 - thermal + electromagnetic trip,
• M250 T - thermal trip only,
• M250 M - electromagnetic trip only,

as well as options with NO/NC auxiliary contacts and enclosures for standalone mounting outside the DIN rail.