Allen-Bradley Servo Motor Part-Number Decoder: MPL / MPM / VPL Series Explained

If you’ve ever looked at an Allen-Bradley servo motor nameplate — something like MPL-B4540F-MK74AA — and wondered whether that string of letters and numbers actually means anything, it does. It’s not decoration. Each segment encodes real information about the motor family, frame size, and configuration, and reading it correctly is the fastest way to identify what you actually have before ordering a repair, replacement, or spare.

The three families you’ll most commonly see

Allen-Bradley’s rotary servo motor nameplates most commonly start with one of these prefixes:

All catalog numbers above are real, verified model numbers from Star Automations’ own product identification records — not illustrative examples.

How to read the structure of the number

The first segment (MPL, MPM, or VPL) identifies the motor series. The next letter — typically a single character like the “B” in MPL-B — is part of what we use internally to group motors into a family for cross-referencing compatible spares and alternatives. Everything after that (frame/winding code, connector or feedback option suffix) narrows down the specific variant: rated torque/power class, and connector or feedback configuration.

The practical rule: two catalog numbers that share the same series-plus-letter prefix (for example, MPL-B430P-MK74AA and MPL-B4540F-MK74AA both starting MPL-B) belong to the same broad family and are the right place to start when looking for a compatible alternative or spare — but the full number still needs to be matched exactly for a true replacement, because the remaining characters encode real differences in rating and configuration.

Why this matters before you order anything

“An Allen-Bradley servo motor” is not a part number — it’s a brand. Even “an MPL motor” isn’t specific enough, since MPL alone covers a wide range of frame sizes and torque ratings. The full catalog number, read character by character off the nameplate, is what actually determines fit, rating, and feedback compatibility. Two units can look similar side by side and still differ in a way that matters the moment you try to wire one in.

What to do with the number once you’ve read it

• Record it exactly as printed — every dash and suffix character matters.
• Photograph the full nameplate, including any secondary label (feedback device details are often on a separate tag).
• Use the series-plus-letter prefix (MPL-B, MPM-B, VPL-B) as your starting point when searching for family-compatible alternatives — then confirm the full number matches before treating anything as a drop-in.

We cover the full identification and compatibility-checking process — voltage, feedback interface, physical mounting — in our companion guide on identifying the right replacement for an obsolete automation part.

Allen-Bradley servo part number — direct answers

What does the “MPL” prefix mean on an Allen-Bradley servo motor?
MPL identifies Allen-Bradley’s low-inertia rotary servo motor series. It’s followed by additional characters encoding frame/winding and configuration details specific to that unit.

Are MPL, MPM, and VPL motors interchangeable?
No — they’re different series (low-inertia, mid-inertia, and high-performance/high-inertia respectively) with different performance characteristics. Even within one series, the full catalog number must match for true interchangeability.

What’s the fastest way to identify my motor before ordering?
Photograph the full nameplate and record the complete catalog number exactly as printed, including all suffix characters — that’s what determines the actual fit and rating, not the series prefix alone.

Send us your nameplate

Have an Allen-Bradley servo motor to identify, repair, or replace? Send the full catalog number and a clear nameplate photo to Ask Star for a review, or browse our shop for verified inventory in this family.