How to read a pool pump motor label

How to Read Pump Motor Labels

To a layperson (and some pool techs) reading a motor label is a sketchy task. As we scour the fading label that contains a jumble of numbers and abbreviations, our brows will furrow in confusion. If this is you, it is ok because you are in the majority rather than the minority. Most with general knowledge can understand horsepower (HP), amps and volts but the rest will look completely foreign.

I would estimate that about half the ratings on the motor are useless (kind of) to the average homeowner. Ratings like Code, Ambient Temp (AMB), Insulation and a few others are chaffe that can distract you from the points on the label that are a necessity in finding a motor replacement. And that brings us to our blog today; we are here to educate you and anyone else who will listen (or read) about the pertinent info on your motor label. With this pertinent info we can know what motor you own and how to find a replacement, if ever that need arises.


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Readers of this article are likely on the hunt for a motor replacement so we will start on the numbers that are most likely to help with that search. Their current motor is Century UST1102-1 (1)likely screeching from bad bearings, or flipping a breaker, and they want to be prepared when it does finally quit. Great plan to think ahead. The key to finding the motor match is using any of follow identification numbers on the motor label.

Catalog (CAT)

The most common identification number on the motor label is the Catalog number; because of its commonness it is the easiest to track a match. CAT numbers have varying formats, for example: UST1102, ST1152, B2854, or B854.

The first format is one that follows the line of UST1102 and ST1152. The UST stands for an uprated motor, “ST-” translates to full rated. The same applies to square flange motors that begin with USQ and SQ. The last four digits show its HP: -1102 = 1 HP, -1152 = 1.5 HP, -1202 = 2 HP and so on.

Another example of a catalog number format is the B854 or B2854. These numbers translate to the same motor; the 2 after the B is a little confusing but essentially is superfluous.

PartCentury B129-1

Century motors have a unique digit based part number format; the basis on their pattern is X-XXXXXX-XX. An example model number is 7-196443-05; either the whole number or the middle six digits can be used to search a match. To my knowledge, there is no rhyme or reason to this numbering system. If there is, please shoot me an email.

Motor Model Number

The motor model number is the longest of all the numbers but its prefix will come in one of three forms: C48, K48 or S48 (for spas.) Following the prefix is a combination number and letters that keep to a pattern as seen in these examples: C48L2N134C1, C48K2N143, K48N2PA105.


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Besides the identification numbers, the motor label contains ratings which can be grouped into two groups: Primary and Secondary. Primary ratings will be the most important ratings to be matched when comparing your old motor label and a prospective replacement. Secondary ratings are ones that are good to understand but will not have much sway in one motor being better than another.

Primary Ratings

  • Horsepower – The unit of measurement by which we measure a motor’s power output. The higher the horsepower the more powerful the motor, in theory. We say in theory because in order to calculate the motor’s “Total HP” we will need the service factor.
  • Service Factor (SF) – Service factor is a multiplier by which we can determine a motor’s “Total HP.”  The formula is thus: HP x SF = Total HP. The service factor defines the motor as either Uprated (1.25 and below) or Full Rated (1.3 and above.)
  • Amps: The motor’s current usage which is the major factor when comparing power consumption of motors
  • Volts – For residential pools, the standard motor volt availability will be 115 or 230. Most mid-range motors like the ¾, 1 and 1.5 HP motors are dual voltage that can run on both 115 or 230. For 2 HP motors and above, those are strictly 230 voltage.
  • Frame (F) – Motors have two distinct flange bolt pattern designs, the Y-Frame (Square) and J-Frame (Round). Motors have two barrel widths rated as either 48 or 56.
Full Rated vs Up Rated


Secondary Ratings

  • Hertz (Hz) – What’s the Frequency, Kenneth? For the United States, the Hz on our appliances is rated 60; for our European friends, they keep it at 50. Hertz is the  measurement of frequency in which the current cycles through a circuit. Some of your home appliances may be labeled as 50/60 because they work on both; but motor labels only work on one or the other.
  • Phase (PH) – Pump motors are available in either Single or Three Phase. The three phase option is used almost exclusively for commercial applications. Single phase motors are the standard in residential pools.
  • RPM – Revolutions Per Minute (RPMs) is the measure of how many times the motor shaft will spin in a minute. Single speed motors run at a standard 3450 RPMs; while dual speed will be rated at 3450/1725 to denote high and low speeds.
  • Duty – Pool motors are marked as Continuous (CONT) duty meaning they can be run 24/7 without detriment to their longevity. To conserve energy, most homeowners run their motor 4-8 hours a day depending on need.
  • Ambient Temp (AMB) – This is the highest outside temperature in which the motor can be used. Don’t worry that your motor says 50 DEGREES; the scale is Celcius so that is actually 122 degrees Fahrenheit.
  • Enclosure (ENCL) – The enclosure types refers to whether the motor is open or closed. All induction motors are “Open” or “Dripproof” to allow for circulation of air to cool the motor. Variable speed motors are sealed because their motor internals do not generate the heat that plagues induction motors.


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2 thoughts on “How to Read Pump Motor Labels

  1. I have found loads of useful info on your website this page in particular. Thank you for sharing.

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