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Allen-Bradley MPL-B420P-SK74AA Low-Inertia Servo Motor
1. Product Overview
The Allen-Bradley MPL-B420P-SK74AA is a high-performance MP-Series MPL low-inertia brushless AC servo motor designed for industrial motion-control applications that require high speed, accurate positioning, fast acceleration, and dependable torque performance.
This model combines a 1.9 kW rated output, 5000 rpm rated speed, 4.74 N·m continuous torque, and 13.5 N·m peak torque in a compact 115 mm frame. It uses a single-turn high-resolution absolute encoder, a keyless shaft extension, a 24 V DC holding brake, and a right-angle SpeedTEC DIN connector.
The SK74AA configuration is particularly useful when a machine requires the advantages of a keyless shaft but also needs an integrated holding brake.
Compared with the SK72AA version, the major difference is the brake configuration. The SK72AA is a no-brake version, while the SK74AA incorporates a 24 V DC holding brake.
That distinction makes the SK74AA a more appropriate choice for applications where the motor or axis must remain mechanically held when servo power is removed.
The motor belongs to the MP-Series MPL low-inertia servo motor family, a product range designed around rapid dynamic response and high-speed industrial motion.
The low-inertia construction is particularly valuable in machinery that repeatedly accelerates, decelerates, indexes, reverses direction, or performs rapid positioning movements.
2. Brand Information
| Item | Information |
|---|---|
| Model | MPL-B420P-SK74AA |
| Brand | Allen-Bradley |
| Product Family | MP-Series MPL |
| Product Type | Low-Inertia Brushless Servo Motor |
| Motor Category | AC Rotary Servo Motor |
| Voltage Class | 400 V AC class |
| Rated Voltage | 460 V AC |
| Primary Application | Industrial Motion Control |
| Configuration | Keyless Shaft + Single-Turn Encoder + 24 V DC Brake |
The Allen-Bradley brand is widely associated with industrial automation and motion-control equipment, and the MPL product family is intended for servo applications where controlled motion and repeatability are important.
For the MPL-B420P-SK74AA specifically, the combination of high-speed operation, low-inertia construction, high-resolution feedback, and an integrated holding brake gives the motor a broad range of possible machine applications.
3. Product Series
MP-Series MPL Low-Inertia Servo Motor Series
The MPL-B420P-SK74AA belongs to the MP-Series MPL low-inertia brushless servo motor series.
The series includes motors with different frame sizes, magnet-stack lengths, feedback systems, shaft configurations, connector arrangements, and brake options.
The B420P motor class is positioned around a 115 mm frame size and 50.8 mm magnet stack length, with a nominal 5000 rpm speed rating.
The B420P family provides 4.74 N·m continuous torque, 13.5 N·m peak torque, and approximately 1.9 kW rated motor output.
The MPL series is particularly suitable for machinery where the motor needs to respond quickly rather than simply operate at a constant speed.
A low-inertia servo motor can change speed rapidly when the drive commands acceleration or deceleration, which is useful in indexing, packaging, assembly, positioning, and other cyclic machine operations.
4. Basic Technical Parameters
| Parameter | Specification |
|---|---|
| Model | MPL-B420P-SK74AA |
| Brand | Allen-Bradley |
| Series | MP-Series MPL |
| Motor Type | Low-Inertia Brushless Servo Motor |
| Voltage Class | 400 V AC |
| Rated Voltage | 460 V AC |
| Rated Power | 1.9 kW |
| Rated Speed | 5000 rpm |
| Maximum Speed | 5000 rpm |
| Continuous Torque | 4.74 N·m |
| Peak Torque | 13.5 N·m |
| Feedback | Absolute Single-Turn High-Resolution Encoder |
| Feedback Resolution | 1024 Sin/Cos |
| Feedback Protocol | Hiperface |
| Shaft | Keyless Shaft Extension |
| Brake | 24 V DC Holding Brake |
| Connector | SpeedTEC DIN Connector |
| Connector Type | Right Angle |
| Connector Rotation | 180° Rotatable |
| Frame Size | 115 mm |
| Magnet Stack Length | 50.8 mm |
| Shaft Seal | No Shaft Seal |
| Protection Rating | IP66 |
| Duty | S1 |
| Rotor Inertia | Approximately 0.00026 kg·m² |
| Approx. Weight | 5.44 kg |
| Dimensions | 115 mm frame / 50.8 mm magnet stack; complete envelope is configuration-dependent |
The product configuration confirms the 460 V rating, 115 mm frame, 50.8 mm magnet stack, 5000 rpm speed, single-turn high-resolution encoder, keyless shaft, right-angle SpeedTEC DIN connector, and 24 V DC brake.
The approximately 5.44 kg weight is an important practical difference when comparing the brake-equipped SK74AA with lighter brake-free configurations.
5. Electrical and Performance Parameters
| Performance Parameter | Value |
|---|---|
| Model | MPL-B420P-SK74AA |
| Rated Voltage | 460 V AC |
| Rated Output | 1.9 kW |
| Rated Speed | 5000 rpm |
| Maximum Speed | 5000 rpm |
| Continuous Torque | 4.74 N·m |
| Peak Torque | 13.5 N·m |
| Rotor Inertia | Approx. 0.00026 kg·m² |
| Duty | S1 |
| Voltage Class | 400 V class |
| Protection | IP66 |
| Approx. Weight | 5.44 kg |
The motor’s 4.74 N·m continuous torque provides the sustained torque capability required by many automated machine axes.
The 13.5 N·m peak torque provides additional short-term capacity during acceleration, deceleration, rapid positioning, or temporary load disturbances.
The peak torque rating should not be treated as a continuous operating value. Actual operation depends on the drive setup, duty cycle, motor temperature, load profile, and application conditions.
6. Mechanical Parameters
| Mechanical Parameter | Specification |
|---|---|
| Model | MPL-B420P-SK74AA |
| Frame Size | 115 mm |
| Magnet Stack Length | 50.8 mm |
| Shaft Type | Keyless |
| Shaft Seal | None |
| Brake | 24 V DC Holding Brake |
| Mounting | IEC Metric |
| Mounting Style | Free Mounting Holes / Type FF |
| Connector | Right-Angle SpeedTEC DIN |
| Connector Rotation | 180° |
| Approx. Weight | 5.44 kg |
| Overall Dimensions | Refer to exact mechanical configuration |
| Frame Dimension | 115 mm |
| Stack Dimension | 50.8 mm |
The 115 mm frame size and 50.8 mm magnet stack are two of the most important physical selection dimensions for this motor.
For machine fabrication, the frame and stack dimensions should not be treated as a substitute for a complete mechanical drawing. Shaft projection, flange dimensions, mounting-hole locations, connector clearance, and total motor envelope should be checked against the exact mechanical drawing before manufacturing the mounting structure.
7. Model Number Explanation
The model designation MPL-B420P-SK74AA can be understood as a combination of motor family and configuration information.
| Model Code | Description |
|---|---|
| MPL | MP-Series MPL servo motor family |
| B | 460 V-class configuration |
| 4 | Frame size 4, approximately 115 mm |
| 20 | 50.8 mm magnet stack |
| P | 5000 rpm speed class |
| S | Single-turn high-resolution encoder |
| K | Keyless shaft extension |
| 7 | SpeedTEC DIN right-angle connector |
| 4 | 24 V DC holding brake |
| AA | Standard configuration designation |
This coding structure makes the model easier to compare with other B420P motors.
For example, changing the final brake configuration from 74 to 72 changes the motor from a brake-equipped configuration to a no-brake configuration while retaining much of the same basic motor platform.
8. Product Introduction
The MPL-B420P-SK74AA is designed for machines where servo motion needs to be fast, repeatable, and accurately controlled.
The motor is not intended simply to rotate at a fixed speed. Its purpose is to work as part of a closed-loop motion system in which the drive continuously monitors motor position and speed and adjusts motor operation according to the machine’s commanded motion.
The motor’s low-inertia construction allows it to react quickly to changes in commanded speed.
This is particularly useful in machinery where the axis repeatedly starts, stops, accelerates, decelerates, or changes direction.
The B420P motor size also provides a useful balance between physical dimensions and torque capability.
With a 115 mm frame and 1.9 kW rated output, the motor can handle applications that may be too demanding for smaller servo motors without immediately moving into a significantly larger motor class.
9. Single-Turn High-Resolution Encoder
The MPL-B420P-SK74AA uses an absolute single-turn high-resolution encoder.
The feedback arrangement is specified as 1024 Sin/Cos, with Hiperface protocol.
The encoder provides the motion-control system with information about motor position and rotational movement.
This is important because servo control depends on accurate feedback.
When the machine commands the motor to move to a particular position, the controller needs reliable feedback to determine whether the motor has reached the desired position.
High-resolution feedback also supports smoother control and more accurate positioning in applications involving repeated indexing or synchronization.
The single-turn design is appropriate for applications where the machine’s required absolute position information is within one mechanical revolution and where multi-turn absolute position tracking is not required.
10. Keyless Shaft Configuration
One of the defining features of the SK74AA is the keyless shaft extension.
Instead of using a traditional shaft key, this configuration is intended for compatible coupling arrangements that secure the shaft through an appropriate clamping mechanism.
This can be useful in compact servo applications where the mechanical transmission system is designed around a keyless coupling.
A keyless connection can also provide a clean mechanical interface when properly installed.
The coupling itself must be selected according to:
- Continuous torque
- Peak torque
- Motor speed
- Shaft dimensions
- Radial load
- Axial load
- Acceleration and deceleration profile
- Coupling stiffness
- Required positioning accuracy
The keyless shaft should therefore be evaluated as part of the complete mechanical transmission rather than as an isolated motor feature.
11. Integrated 24 V DC Holding Brake
The biggest functional distinction between the SK74AA and the SK72AA configuration is the integrated 24 V DC holding brake.
The brake is useful when the machine needs the motor axis to remain mechanically held after the servo system removes motor torque.
This can be particularly important for vertical axes.
For example, a vertical actuator may naturally move downward under gravity if motor torque is removed.
In such a situation, an integrated holding brake can provide an additional mechanical holding function.
The brake is not intended to replace proper machine safety design or to act as a general-purpose dynamic stopping device.
The brake should be applied and controlled according to the motor and motion-system requirements.
12. High-Speed 5000 RPM Operation
The motor is rated for 5000 rpm.
This makes it suitable for applications where machine throughput depends on fast rotary motion.
High-speed operation is especially valuable in:
- Packaging machinery
- Indexing systems
- Rotary positioning
- Pick-and-place systems
- Material feeding
- Converting equipment
- Automated assembly
- High-speed production machinery
The 5000 rpm capability also gives the machine designer more flexibility when selecting gear ratios and mechanical transmission arrangements.
13. Continuous Torque and Peak Torque
The motor provides approximately 4.74 N·m continuous torque.
This represents the sustained torque capability and is one of the most important values when sizing the motor for an application.
The peak torque is approximately 13.5 N·m.
Peak torque is useful during acceleration and deceleration when the motor temporarily needs considerably more torque than during steady-state operation.
A machine with frequent acceleration and deceleration can therefore benefit from the motor’s relatively high peak-to-continuous torque ratio.
Correct motor sizing should always consider the complete motion profile rather than simply comparing continuous torque values.
14. IP66 Protection
The MPL-B420P-SK74AA is specified with an IP66 protection rating.
This provides a good level of protection against dust and water exposure in many industrial environments.
The protection rating is useful in automated machinery where the motor may be exposed to dust, airborne particles, or occasional water spray.
However, IP66 should not be interpreted as universal protection against every industrial chemical or environmental condition.
Where the motor is exposed to aggressive chemicals, extreme temperatures, continuous washdown, corrosive substances, or other unusual conditions, the complete installation environment should be evaluated.
15. SpeedTEC DIN Connector
The motor uses a right-angle SpeedTEC DIN connector with a 180-degree rotatable arrangement.
This is useful when the motor is installed in a confined machine area.
The ability to orient the connector can make cable routing easier and reduce interference with machine frames, guards, couplings, gearboxes, and moving components.
Good cable routing is particularly important in servo systems because the motor and feedback cables must remain properly connected throughout repeated machine movement.
16. Main Product Advantages
16.1 High-Speed Servo Performance
The 5000 rpm rating allows the motor to support high-speed machine operation.
This can be useful for reducing cycle times and increasing production throughput.
16.2 Strong Continuous Torque
The 4.74 N·m continuous torque rating gives the motor enough sustained output for many medium-duty industrial servo axes.
It provides a useful step up from smaller MPL motor sizes.
16.3 High Peak Torque
The 13.5 N·m peak torque capability allows the motor to handle demanding acceleration and deceleration profiles.
This is particularly valuable in machines with frequent starts and stops.
16.4 Low-Inertia Rotor
The low-inertia construction helps the motor respond quickly to changes in commanded speed.
This is one of the major reasons the MPL family is attractive for dynamic motion applications.
16.5 High-Resolution Feedback
The single-turn high-resolution encoder provides detailed motor-position feedback.
This supports accurate closed-loop servo control and repeatable machine positioning.
16.6 Integrated Holding Brake
The 24 V DC brake gives the SK74AA an important advantage over brake-free versions.
It is particularly useful where the motor axis must remain mechanically held after servo power is removed.
16.7 Keyless Shaft
The keyless shaft can simplify mechanical integration when the machine uses an appropriate clamping coupling.
It also allows the machine designer to use a transmission system specifically designed for keyless servo shafts.
16.8 Compact 115 mm Frame
The 115 mm frame offers a useful balance between torque capability and physical size.
The motor provides 1.9 kW output without requiring the much larger physical envelope associated with higher-power motor classes.
16.9 IP66 Protection
The IP66 enclosure rating makes the motor suitable for many industrial environments where dust and water protection are required.
16.10 Flexible Connector Orientation
The right-angle connector with 180-degree rotation provides additional installation flexibility.
This is especially useful when machine space is restricted.
17. Typical Applications
Packaging Machines
The motor is well suited to packaging equipment where rapid, repeatable movement is required.
Possible applications include:
- Packaging indexing
- Product feeding
- Cutting mechanisms
- Film handling
- Rotary positioning
- Sealing mechanisms
- Product transfer
The low-inertia design is especially useful when the machine operates through repeated short motion cycles.
Automated Assembly Machines
Automated assembly equipment frequently requires accurate positioning and synchronization.
The MPL-B420P-SK74AA can be used for rotary axes, indexing mechanisms, transfer systems, and synchronized machine movements.
The encoder provides feedback for accurate positioning while the brake can provide additional holding capability where required.
Vertical Positioning Systems
The integrated 24 V DC holding brake makes the SK74AA particularly interesting for applications involving vertical motion.
A vertical axis can require mechanical holding when servo torque is removed.
The brake-equipped configuration provides an additional mechanical holding function that may not be available with the SK72AA no-brake configuration.
The actual brake capacity and machine safety requirements must always be evaluated for the specific load.
Material Handling
The motor can be used for controlled material-handling equipment, including:
- Conveyor positioning
- Transfer mechanisms
- Rotary transfer units
- Automated feeders
- Indexing systems
- Product alignment mechanisms
Pick-and-Place Systems
Pick-and-place machines often require rapid acceleration and precise stopping.
The low-inertia rotor can be advantageous for these high-cycle applications.
The motor can accelerate quickly, move the mechanism to its target position, decelerate, and repeat the cycle.
Rotary Indexing Equipment
Rotary indexing tables require accurate movement from one position to another.
The MPL-B420P-SK74AA can provide controlled rotary motion while its brake offers additional holding functionality when required by the machine design.
Machine Automation
The motor can be considered for various automated production machines where:
- Speed is important
- Positioning accuracy is important
- Repeated acceleration is required
- Continuous torque is moderate to high
- Short-term peak torque is required
- Mechanical holding may be necessary
18. Five Related Models in the Same Series
The following models are closely related to the MPL-B420P-SK74AA and are useful when comparing shaft, brake, and feedback configurations.
| Model | Feedback | Shaft | Brake | Speed | Continuous Torque | Peak Torque | Power | Frame / Stack | Weight |
|---|---|---|---|---|---|---|---|---|---|
| MPL-B420P-SK72AA | Single-turn high-resolution | Keyless | No brake | 5000 rpm | 4.74 N·m | 13.5 N·m | 1.9 kW | 115 / 50.8 mm | Approx. 5.44 kg |
| MPL-B420P-SJ72AA | Single-turn high-resolution | Keyed | No brake | 5000 rpm | 4.74 N·m | 13.5 N·m | 1.9 kW | 115 / 50.8 mm | Approx. 4.3–5.4 kg |
| MPL-B420P-SJ74AA | Single-turn high-resolution | Keyed | 24 V DC brake | 5000 rpm | 4.74 N·m | 13.5 N·m | 1.9 kW | 115 / 50.8 mm | Approx. 5.4 kg |
| MPL-B420P-RJ74AA | Resolver | Keyed | 24 V DC brake | 5000 rpm | 4.74 N·m | 13.5 N·m | 1.9 kW | 115 / 50.8 mm | Approx. 5.4 kg |
| MPL-B420P-MJ74AA | Absolute multi-turn | Keyed | 24 V DC brake | 5000 rpm | 4.74 N·m | 13.5 N·m | 1.9 kW | 115 / 50.8 mm | Approx. 5.4 kg |
The five models are closely related because they use the same general B420P motor platform.
The primary differences are the shaft configuration, feedback technology, and brake configuration.
This is important when selecting a replacement because two motors can have the same power, torque, speed, and frame dimensions while still requiring different drive configuration or mechanical coupling arrangements.
19. Five Popular Allen-Bradley Models for Comparison
The following models are useful comparison products within the same general servo motor range.
| Model | Series | Rated Power | Continuous Torque | Peak Torque | Speed | Feedback | Frame / Stack | Approx. Weight |
|---|---|---|---|---|---|---|---|---|
| MPL-B310P-SJ74AA | MP-Series MPL | 0.77 kW | 1.58 N·m | 3.61 N·m | 5000 rpm | Single-turn high-resolution | 100 mm / 25.4 mm | Approx. 2.7 kg |
| MPL-B320P-SJ74AA | MP-Series MPL | 1.5 kW | 3.05 N·m | 7.91 N·m | 5000 rpm | Single-turn high-resolution | 100 mm / 50.8 mm | Approx. 3.7 kg |
| MPL-B330P-SJ74AA | MP-Series MPL | 1.8 kW | 4.18 N·m | 11.1 N·m | 5000 rpm | Single-turn high-resolution | 100 mm / 76.2 mm | Approx. 4.6 kg |
| MPL-B420P-SK74AA | MP-Series MPL | 1.9 kW | 4.74 N·m | 13.5 N·m | 5000 rpm | Single-turn high-resolution | 115 mm / 50.8 mm | Approx. 5.44 kg |
| MPL-B430P-SJ74AA | MP-Series MPL | 2.2 kW | 6.55 N·m | 19.8 N·m | 5000 rpm | Single-turn high-resolution | 115 mm / 76.2 mm | Approx. 5.5 kg |
The B310P, B320P, B330P, B420P, and B430P models form a useful progression in terms of output capability.
The B420P is especially interesting because it provides nearly 2 kW of rated power while maintaining a 5000 rpm speed rating and a relatively compact 115 mm frame.
The B430P increases the continuous and peak torque capability while maintaining the same general high-speed class. The published motor data lists the B420P at 4.74 N·m continuous torque and 13.5 N·m peak torque, while the B430P is rated at 6.55 N·m continuous torque and 19.8 N·m peak torque.
20. SK74AA Compared With SK72AA
| Parameter | MPL-B420P-SK74AA | MPL-B420P-SK72AA |
|---|---|---|
| Voltage | 460 V AC | 460 V AC |
| Power | 1.9 kW | 1.9 kW |
| Speed | 5000 rpm | 5000 rpm |
| Continuous Torque | 4.74 N·m | 4.74 N·m |
| Peak Torque | 13.5 N·m | 13.5 N·m |
| Feedback | Single-turn high-resolution | Single-turn high-resolution |
| Shaft | Keyless | Keyless |
| Brake | 24 V DC | No brake |
| Frame | 115 mm | 115 mm |
| Magnet Stack | 50.8 mm | 50.8 mm |
| Protection | IP66 | IP66 |
| Approx. Weight | 5.44 kg | Approx. 5.44 kg |
The two models are mechanically and electrically similar in their basic motor characteristics.
The key difference is the brake.
The SK74AA should be considered when the application requires an integrated holding brake.
The SK72AA is more appropriate when no motor brake is required.
21. SK74AA Compared With SJ74AA
| Parameter | MPL-B420P-SK74AA | MPL-B420P-SJ74AA |
|---|---|---|
| Feedback | Single-turn high-resolution | Single-turn high-resolution |
| Shaft | Keyless | Keyed |
| Brake | 24 V DC | 24 V DC |
| Speed | 5000 rpm | 5000 rpm |
| Power | 1.9 kW | 1.9 kW |
| Continuous Torque | 4.74 N·m | 4.74 N·m |
| Peak Torque | 13.5 N·m | 13.5 N·m |
| Frame | 115 mm | 115 mm |
| Magnet Stack | 50.8 mm | 50.8 mm |
| Approx. Weight | 5.44 kg | Approx. 5.4 kg |
The difference here is primarily mechanical.
The SK74AA uses a keyless shaft, while the SJ74AA uses a keyed shaft.
If the machine transmission is designed for a clamping coupling, the SK74AA is generally the more natural configuration.
If the existing machine uses a conventional keyed coupling, the SJ74AA may be easier to integrate.
22. SK74AA Compared With a Higher-Torque B430P
| Parameter | MPL-B420P-SK74AA | MPL-B430P-SJ74AA |
|---|---|---|
| Rated Power | 1.9 kW | 2.2 kW |
| Rated Speed | 5000 rpm | 5000 rpm |
| Continuous Torque | 4.74 N·m | 6.55 N·m |
| Peak Torque | 13.5 N·m | 19.8 N·m |
| Frame | 115 mm | 115 mm |
| Stack Length | 50.8 mm | Approx. 76.2 mm |
| Approx. Weight | 5.44 kg | Approx. 5.5 kg |
| Brake | 24 V DC | 24 V DC |
| Feedback | Single-turn high-resolution | Single-turn high-resolution |
The B430P is the more suitable choice when the machine requires additional torque capacity.
The B420P, however, can be preferable where 4.74 N·m continuous torque is sufficient and a shorter magnet-stack configuration is beneficial.
This distinction can be important in compact machine designs.
23. Application Selection Guide
| Application Requirement | Recommended Configuration |
|---|---|
| High-speed horizontal axis | MPL-B420P-SK74AA |
| Horizontal axis without brake requirement | MPL-B420P-SK72AA |
| Keyed shaft required | MPL-B420P-SJ74AA |
| Keyless shaft required | MPL-B420P-SK74AA |
| Vertical axis requiring holding | MPL-B420P-SK74AA |
| Multi-turn absolute feedback required | MPL-B420P-MJ74AA |
| Resolver feedback required | MPL-B420P-RJ74AA |
| More continuous torque required | MPL-B430P family |
| Lower-power application | MPL-B310P / B320P / B330P |
This table provides a practical way to narrow down the motor configuration.
The first step should be to determine the required continuous torque and peak torque.
The next step should be to determine the required speed.
After that, the machine designer should evaluate feedback requirements, shaft type, brake requirements, mounting dimensions, connector arrangement, and environmental conditions.
24. Installation Considerations
The MPL-B420P-SK74AA should be mounted to a rigid machine structure capable of maintaining correct shaft alignment.
Poor alignment can place unnecessary radial and axial loads on the motor bearings.
The keyless shaft also requires particular attention to coupling installation.
The coupling should be properly aligned and tightened according to the coupling manufacturer’s requirements.
The motor’s high-speed capability means that even small mechanical alignment problems can become more noticeable as operating speed increases.
Cable routing should also be planned before installation.
The right-angle connector can be rotated to improve cable routing, but adequate clearance should still be maintained around the connector and cable assembly.
25. Brake Installation Considerations
The integrated 24 V DC brake is an important feature of the SK74AA.
However, the brake should be viewed primarily as a holding brake, not as a general-purpose dynamic stopping device.
For a vertical axis, the brake may be used to hold the load when motor torque is removed.
The machine control system should coordinate servo torque and brake operation appropriately.
The actual load, vertical travel, inertia, stopping requirements, and safety requirements should all be evaluated before relying on the brake as part of the machine’s holding system.
26. Maintenance Considerations
A servo motor can operate for long periods in industrial machinery, but correct installation and operating conditions remain important.
The motor should be kept within the specified temperature range.
The mounting structure should remain rigid.
The coupling should be checked for alignment and mechanical condition.
The motor cable and feedback connection should also be inspected periodically.
Because servo control depends heavily on feedback, loose or damaged feedback connections can create positioning problems even when the motor itself is mechanically healthy.
The holding brake should also be considered during maintenance.
If the machine depends on the brake for holding a vertical load, the brake’s condition should be included in the machine’s maintenance program.
27. Replacement Selection Checklist
When replacing an existing motor with an MPL-B420P-SK74AA, the following parameters should be checked carefully.
| Check Item | Required Specification |
|---|---|
| Model | MPL-B420P-SK74AA |
| Brand | Allen-Bradley |
| Series | MP-Series MPL |
| Voltage | 460 V AC |
| Power | 1.9 kW |
| Rated Speed | 5000 rpm |
| Maximum Speed | 5000 rpm |
| Continuous Torque | 4.74 N·m |
| Peak Torque | 13.5 N·m |
| Feedback | Single-turn high-resolution |
| Encoder | 1024 Sin/Cos |
| Shaft | Keyless |
| Brake | 24 V DC holding brake |
| Frame | 115 mm |
| Magnet Stack | 50.8 mm |
| Connector | SpeedTEC DIN right angle |
| Protection | IP66 |
| Approx. Weight | 5.44 kg |
| Rotor Inertia | Approx. 0.00026 kg·m² |
A replacement motor should not be selected based only on the model’s power rating.
The feedback system, shaft design, brake configuration, connector type, mounting dimensions, speed, torque, and motor-drive compatibility all need to be checked.
28. Main Advantages at a Glance
| Advantage | Description |
|---|---|
| 5000 rpm High-Speed Capability | Suitable for fast machine cycles |
| 1.9 kW Output | Provides useful power for medium-duty servo axes |
| 4.74 N·m Continuous Torque | Supports sustained mechanical loads |
| 13.5 N·m Peak Torque | Provides additional acceleration capability |
| Low Rotor Inertia | Supports fast dynamic response |
| Single-Turn High-Resolution Feedback | Provides accurate closed-loop position information |
| Keyless Shaft | Suitable for compatible clamping couplings |
| 24 V DC Holding Brake | Useful for holding applications and selected vertical axes |
| 115 mm Frame | Good balance between size and output |
| 50.8 mm Stack | Compact B420P motor configuration |
| IP66 Protection | Suitable for many industrial environments |
| Rotatable Right-Angle Connector | Provides greater installation flexibility |
| Industrial Servo Construction | Suitable for repetitive automated motion |
29. Why Choose the SK74AA Instead of the SK72AA?
The decision between these two models is relatively straightforward.
If the machine does not need a holding brake, the SK72AA provides a simpler no-brake configuration.
If the machine needs an integrated holding brake, the SK74AA is the more suitable choice.
This is especially relevant for:
- Vertical axes
- Lifting mechanisms
- Positioning systems that must remain stationary after power removal
- Machines requiring mechanical holding
- Applications where an integrated motor brake simplifies the mechanical design
The two models share the same basic B420P motor performance, so the brake requirement becomes one of the most important factors in the selection decision.
30. Why Choose the SK74AA Instead of a Smaller Motor?
The B420P configuration provides 4.74 N·m continuous torque and 13.5 N·m peak torque.
A smaller B310P, B320P, or B330P motor may be adequate for lower-load applications, but the B420P provides a higher level of continuous and peak torque.
This makes it useful when the machine load has increased or when acceleration requirements have become more demanding.
For example, if a B320P installation is operating close to its torque limit, moving to the B420P can provide additional capacity without immediately moving to a much larger servo motor class.
31. Overall Product Evaluation
The Allen-Bradley MPL-B420P-SK74AA is a strong choice for industrial motion systems that require a combination of high speed, moderate-to-high torque, low inertia, high-resolution feedback, keyless mechanical connection, and integrated holding capability.
Its 5000 rpm speed rating makes it suitable for high-cycle equipment.
Its 4.74 N·m continuous torque provides useful sustained mechanical output.
Its 13.5 N·m peak torque provides additional capacity during acceleration and rapid positioning.
The 115 mm frame keeps the motor relatively compact for its performance level.
The keyless shaft is useful for compatible coupling systems, while the 24 V DC holding brake makes the motor more versatile than the corresponding no-brake configuration.
The single-turn high-resolution encoder provides the feedback needed for accurate servo control.
Taken together, these characteristics make the MPL-B420P-SK74AA a practical motor for automated machinery where both dynamic performance and mechanical holding are important.
32. Final Product Summary
The Allen-Bradley MPL-B420P-SK74AA is an MP-Series MPL low-inertia brushless AC rotary servo motor with a 460 V AC rating, 1.9 kW rated output, 5000 rpm rated speed, 4.74 N·m continuous torque, and 13.5 N·m peak torque.
Its physical configuration includes a 115 mm frame, 50.8 mm magnet stack, keyless shaft extension, right-angle SpeedTEC DIN connector, and an integrated 24 V DC holding brake.
The motor uses a single-turn high-resolution absolute encoder with 1024 Sin/Cos feedback, making it suitable for accurate closed-loop motion applications.
The approximately 5.44 kg motor weight should also be considered during machine design, particularly where the motor is mounted on moving equipment or a compact mechanical axis.
The motor’s main advantages can be summarized as follows:
- High 5000 rpm operating speed
- 1.9 kW rated power
- 4.74 N·m continuous torque
- 13.5 N·m peak torque
- Low-inertia rotor design
- High-resolution single-turn feedback
- Keyless shaft
- Integrated 24 V DC holding brake
- 115 mm compact frame
- 50.8 mm magnet stack
- IP66 protection
- Flexible right-angle connector arrangement
For packaging equipment, automated assembly machinery, rotary indexing systems, pick-and-place machines, material-handling equipment, vertical positioning axes, and other industrial automation systems, the MPL-B420P-SK74AA offers a balanced combination of speed, torque, feedback performance, and mechanical flexibility.
The most important point when selecting this model is its SK74AA configuration: the motor combines a keyless shaft with a 24 V DC holding brake.
If a machine requires the same general B420P motor performance but does not need a brake, the SK72AA configuration is the more direct alternative.
If a keyed shaft is required, the SJ74AA configuration is a closer mechanical alternative.
If multi-turn absolute feedback is required, the MJ74AA configuration should be considered instead.
Overall, the MPL-B420P-SK74AA is best suited to industrial servo applications where fast, repeatable motion is combined with a requirement for reliable mechanical holding.