Product Description

Ziehl-Abegg RH25M-2DK.1E.2R — M-Series Single-Flow Centrifugal Fan, 0.25 kW

Cooling systems inside electrical cabinets, air handling units, refrigeration equipment, and climate control units all share the same fundamental requirement: move a defined volume of air reliably, continuously, and quietly — for years, without maintenance. A fan that fails in a drive cabinet brings down a production line. A fan that vibrates excessively destroys the bearings of neighboring components. A fan that overheats due to a blocked airflow path and lacks any protection mechanism becomes a fault source with no warning.

The RH25M-2DK.1E.2R is Ziehl-Abegg's M-series answer to those requirements at the 250 mm impeller size class. Three-phase AC motor integrated directly into the impeller hub. Hybrid bearings for extended service life and quieter operation. Pre-terminated shielded cable for straightforward electrical connection. 0.25 kW at 2,800 rpm on a compact, self-contained unit that drops into a standard fan mounting cutout.

Genuine Ziehl-Abegg manufacture, Germany. Brand new original stock. In stock and available for immediate worldwide dispatch.

Technical Specifications

Parameter	Value
Model Number	RH25M-2DK.1E.2R
Ziehl-Abegg Article No.	172135 / 170155
Fan Series	M-Series (Motor Fan Wheel)
Fan Type	Single-flow centrifugal fan
Nominal Impeller Diameter	250 mm
Motor Poles	2-pole
Rated Power	0.25 kW
Rated Voltage	3-phase 230/400 V ±10% (Δ/Y)
Frequency	50/60 Hz
Rated Current	~0.48–0.50 A
Rated Speed (50 Hz)	~2,800–2,820 rpm
Thermal Protection	Without (winding without thermal protection)
Bearing Type	Hybrid bearings
Protection Class	IP44
Connection Cable	Shielded, L = 105 cm
Scatter Type	Without scattering, Type K02
Max. Air Temperature	70°C
Item Weight	4.50 kg
Shipping Weight	5.50 kg
Shipping Dimensions	50 × 40 × 40 cm
Country of Origin	Germany

The M-Series Architecture: Motor Integrated into the Impeller

What makes the Ziehl-Abegg M-series mechanically distinctive is immediately visible when you look at one: there is no external motor housing, no shaft coupler, no separate motor-to-impeller bracket. The AC motor stator sits inside a compact housing at the centre of the impeller assembly, and the impeller itself is the rotor — mounted directly on the motor shaft, or in some configurations, with the rotor integrated into the impeller hub. The result is a single compact unit with the motor and fan wheel sharing one set of bearings and one rotating assembly.

This integrated design has several practical consequences. Cabinet depth required for the fan-plus-motor assembly is minimised compared to separate motor and impeller configurations. There are no alignment issues between motor shaft and impeller. Vibration from misalignment — one of the more common causes of premature bearing failure in fan systems — is eliminated by design. And the overall unit weight and footprint remain compact relative to the airflow delivered.

The "M" in RH25M specifically denotes this motor fan wheel construction within Ziehl-Abegg's product classification. The RH prefix identifies the radial (centrifugal) fan type, and 25 identifies the 250 mm nominal impeller diameter size class.

Centrifugal Fan vs. Axial Fan: Understanding the Application Fit

The RH25M-2DK.1E.2R is a centrifugal (radial) fan — not an axial fan — and the distinction matters for system integration.

An axial fan moves air parallel to its rotation axis, like a propeller. It handles high flow volumes at low static pressure and is the right choice for applications where there is minimal resistance to airflow — open cabinet ventilation, free-blowing air circulation. When ducted against any significant back-pressure, axial fan performance drops sharply.

A centrifugal fan moves air perpendicular to its rotation axis: air enters through the eye of the impeller axially and exits radially at the periphery. Centrifugal fans generate significantly higher static pressure at a given flow rate. This makes them the correct choice wherever airflow passes through filters, heat exchangers, coils, ductwork restrictions, or any other system component that creates resistance. In climate control equipment, refrigeration condensers and evaporators, and air handling units with internal heat exchangers, centrifugal fans are the standard rather than axial — the system pressure drop demands it.

The RH25M-2DK.1E.2R operates in this regime. Its single-flow impeller draws air in from one side (single inlet) and discharges it radially, developing the static pressure necessary to push air through the thermal management components of the equipment it serves.

Hybrid Bearings: What They Are and Why They Matter

Standard AC fan motors use either grease-lubricated deep groove ball bearings (steel balls, steel races) or sleeve bearings. The RH25M-2DK.1E.2R is specified with hybrid bearings — a construction where the rolling elements (balls) are ceramic (typically silicon nitride, Si₃N₄) running in steel outer and inner races.

Ceramic balls are significantly harder than steel, with lower density and lower thermal expansion. In bearing terms this translates to several practical advantages: reduced friction at the ball-race contact, lower heat generation at high speed, reduced electrical conductivity through the bearing (relevant in applications where stray motor currents can erode bearing surfaces), and longer fatigue life under equivalent load conditions compared to all-steel bearings.

For a fan that runs continuously in an HVAC or cooling application — powered up for thousands of hours per year — the choice of bearings directly determines how long the fan operates before the bearings reach end-of-life. Hybrid bearings extend that interval meaningfully compared to standard steel bearings, reducing the frequency of planned maintenance replacements and the risk of unplanned bearing failures.

Shielded Cable, 105 cm: Ready for Direct Termination

The ".1E" code in the model designation identifies the cable configuration: a shielded cable, 105 cm length. The cable exits the motor winding and terminates in flying leads, pre-cut to 105 cm, ready for direct connection to a terminal strip or contactor.

The shielding is relevant in environments where the fan is installed adjacent to variable frequency drives, power electronics, or other sources of conducted electromagnetic interference. An unshielded motor cable in such an environment can act as an antenna, both radiating interference outward and picking up noise that can disturb sensitive instrumentation nearby. The shield provides a defined return path for high-frequency noise currents, keeping the motor cable's EMI contribution within acceptable bounds.

At 105 cm, the cable is long enough to reach a terminal strip in a typical cabinet without extension, while remaining manageable in confined spaces. Excess length can be coiled and secured rather than trimmed.

Winding Without Thermal Protection — Installation Implications

The "-2DK" motor code and the ICDC parts description both confirm: this motor is wound without integrated thermal protection (no thermistor, no thermal switch embedded in the winding). This means there is no internal device that will interrupt the motor circuit if the winding overheats.

In a standard installation, this is not a deficiency — it is a design choice that shifts thermal protection responsibility to the external panel design. The motor must be protected by a correctly sized motor protection relay or circuit breaker in the panel, set to trip at or below the motor's rated current. The installer is responsible for ensuring that external overload protection is provided.

For applications where winding temperature monitoring is required — for predictive maintenance systems or safety-rated circuits — an external temperature monitoring solution must be provided separately.

IP44 Protection: Suitable for Indoor HVAC Equipment

The IP44 rating covers the motor and fan assembly against solid particle ingress (protected against objects greater than 1 mm) and water splash from any direction. In the context of the applications this fan serves — climate control units, air handling equipment, refrigeration cabinets, cooling coil sections — IP44 is the standard protection level. The fan is not exposed to direct water jets or immersion, but condensation, splashing from coil drip, and airborne moisture in humid environments are all within the protection envelope.

IP44 is not rated for outdoor installation in rain or washdown environments. For those applications, Ziehl-Abegg offers variants with higher IP ratings from the same product family.

Frequently Asked Questions

Q: Is this an axial fan or a centrifugal fan?

A: This is a centrifugal (radial) fan. The RH prefix in Ziehl-Abegg's naming convention designates the radial fan family. Air enters axially through the impeller inlet and is discharged radially at the periphery. Centrifugal fans develop significantly higher static pressure than axial fans, making them appropriate for applications with internal airflow resistance — heat exchangers, filters, coils, and ductwork. If your application requires an axial (propeller-type) fan, Ziehl-Abegg's FB and FN series are the relevant products to consider instead.

Q: What does the model number RH25M-2DK.1E.2R mean?

A: The model code encodes the key configuration parameters. RH = radial (centrifugal) fan, M-series (motor fan wheel). 25 = 250 mm nominal impeller diameter. 2 = 2-pole motor (nominally 2800 rpm at 50 Hz). DK = motor type/winding code. 1E = cable type (shielded, 105 cm). 2R = variant designation within the configuration matrix. Together these parameters uniquely identify the voltage, power, bearing, and cable configuration of this specific unit.

Q: What three-phase voltage supply does this fan require?

A: The motor is wound for 3-phase 230/400 V ±10% (Delta/Star connection). At 230V three-phase (Delta), connect line-to-line at 230V. At 400V three-phase (Star), connect line-to-neutral at 230V with 400V line-to-line. Both connections produce the same operating speed and power output. Verify the available supply voltage before connection and configure the motor terminal board accordingly.

Q: Does the motor have built-in thermal protection?

A: No. The RH25M-2DK.1E.2R is wound without integrated thermal protection — there is no embedded thermistor or bi-metallic thermal switch in the winding. External motor overload protection must be provided in the electrical panel: a thermal overload relay, electronic motor protection relay, or motor circuit protector (MCP) sized to the motor's rated current. This is standard installation practice for industrial fan motors and does not represent a limitation unique to this model.

Q: What are the hybrid bearings, and how do they compare to standard bearings?

A: Hybrid bearings use ceramic (silicon nitride) rolling elements in steel races, compared to all-steel rolling elements in standard bearings. Ceramic balls are harder, lighter, and generate less friction at the contact point than steel balls. The practical result is lower operating temperature, reduced electrical conductivity through the bearing path, and longer fatigue life under continuous operation. For fans running 8,000+ hours per year in HVAC and cooling equipment, hybrid bearings extend the service interval before bearing replacement becomes necessary.

Q: What equipment is this fan typically used in?

A: The RH25M size class and centrifugal fan design make it a common choice for: air handling units (AHU) and fan coil units, refrigeration and heat pump systems (condenser and evaporator sections), electrical cabinet and drive enclosure cooling, industrial cooling coil sections, and climate control equipment in telecommunications and data installations. The 0.25 kW power level and 250 mm impeller size suit medium airflow requirements at moderate static pressure — typical of single-zone HVAC and enclosed equipment cooling.

Q: Can this fan be speed-controlled with a variable frequency drive (VFD)?

A: The motor is a standard three-phase AC induction design and is electrically compatible with VFD speed control. However, since the motor is wound without integrated thermal protection, the installer must ensure that the VFD's motor protection parameters are correctly set for this motor's rated current. Running the motor at very low speeds for extended periods may reduce its self-cooling (the impeller's own airflow cools the motor at rated speed), so minimum speed limits should be respected — typically above 30–40 Hz for continuous operation unless the installation provides supplementary cooling.

Q: Is this the same as Ziehl-Abegg article number 170155 or 172135?

A: Both article numbers refer to the RH25M-2DK.1E.2R model. Ziehl-Abegg has used both 170155 and 172135 as article numbers for this configuration across different catalogue editions and production batches. The model designation RH25M-2DK.1E.2R is the definitive part number for ordering and cross-referencing. When replacing an existing unit, verify the model number from the motor label rather than relying solely on the article number.

RH25M-2DK.1E.2R Genuine RH25M-2DK.1E.2R ZIEHL-ABEGG Fan Axial Cooling Fan