Your worm gear reducer is ready, you have selected the output speed and the ratio; all that remains is to mount the right electric motor onto the reducer housing. And this is exactly where the most common field mistake begins: the motor power does not match the reducer housing, or the flange type (B5 or B14) is wrong and the motor simply will not seat onto the reducer. In this article we explain, step by step, how to choose a motor for a worm gear reducer housing: how many kW for which HEM housing, which IEC frame size and which flange fits. Our goal is not to discuss price; it is to help you order the motor that fits your reducer exactly, correctly the first time.

As HEM Motor, we have manufactured both electric motors and worm gear reducers since 1979. That means the reducer and the motor come off the same bench, in dimensions that match each other. Thanks to our strong stock in Turkiye, we can usually match and ship a suitable electric motor for housings from HEM30 up to HEM130 on the same day.

This guide does not get into price factors; our focus here is purely technical matching. In other words, we answer the question "which motor fits my reducer" clearly, housing by housing, kW by kW, flange by flange. If you are separately curious about what determines worm gear reducer prices, you can read our article on factors affecting worm gear reducer prices; here, our only subject is correct motor selection.

Mounting a B5 flanged electric motor onto a worm gear reducer and IEC frame matching

The Field Cost of Choosing the Wrong Motor

A motor that does not fit the reducer is not just an ordering error; it means production stoppage, return-shipping cost and lost delivery time. The most frequent incompatibilities are these: the motor power is selected too large for the housing and strains the gear; the IEC frame size does not seat into the reducer input bore; a B14 (instead of B5, or vice versa) flanged motor is ordered; or the input speed is wrong (for example a 2-pole 2800 rpm motor instead of a 4-pole one) so the output speed does not match. All of these mistakes can be prevented by clarifying the reducer housing and the desired output speed at the very start. The purpose of this article is precisely to provide that clarity.

The Logic of Selecting a Motor for a Worm Gear Reducer Housing

In a worm gear reducer, the worm screw driven by the motor turns the bronze gear and transmits motion to the output shaft. In this structure, the motor must satisfy three conditions for the reducer:

  • Power (kW): The motor power must fall within the power range that the reducer housing can carry. Fitting an oversized motor strains the gear; an underpowered one cannot lift the load.
  • IEC frame size: The reducer input flange is bored for specific IEC frames (56, 63, 71, 80, 90, 100, 112, 132, 160). The motor frame size must seat into that bore.
  • Flange type (B5/B14): The reducer input is selected for either a B5 (large flange) or a B14 (small flange) connection; the motor flange must match it.

In standard practice, a 1400-1500 rpm (4-pole) asynchronous motor is coupled to the reducer input; the output speed is then determined by the reduction ratio you select (for example, a 1/30 ratio with a 1400 rpm input gives roughly 46 rpm output).

Without all three of these conditions (power, IEC frame, flange) being satisfied together, the motor cannot be mounted to the reducer. If one of the three does not match, the motor either physically will not seat, or it seats but creates performance and lifespan problems. That is why, in the next sections, we provide these three values as a table for each HEM housing. When using the table, first determine your reducer housing, then choose the power suitable for your application from that row's kW range and the IEC/flange option that fits your mounting. If you follow this order, your chance of making a mistake drops to nearly zero.

kW and IEC Connection Table by HEM Housing

The values below are the real catalog data of the HEM worm gear reducer series. Once you have determined your reducer housing, you can see the suitable motor power and IEC connection option here.

Small and Medium Housings (HEM30 - HEM63)

  • HEM30: 0.06-0.18 kW motor. Connection: 56B5, 56B14, 63B5, 63B14 (IEC 56 and IEC 63 frames, B5 or B14 flange).
  • HEM40: 0.12-0.37 kW motor. Connection: IEC 63 B5/B14, IEC 71 B5/B14.
  • HEM50: 0.18-0.75 kW motor. Connection: IEC 63, 71 and 80 frames, B5/B14.
  • HEM63: 0.37-1.5 kW motor. Connection: IEC 71, 80 and 90 frames, B5/B14.

Larger Housings (HEM75 - HEM130)

  • HEM75: 0.75-3 kW motor. Connection: IEC 80, 90 and 100 frames, B5/B14.
  • HEM90: Couples with IEC standard frame, B5 or B14 flanged motors; used in the medium-to-upper power range.
  • HEM110: 2.2-7.5 kW motor. Connection: IEC 100, 112 and 132 frames, B5/B14.
  • HEM130: 4-11 kW motor. Connection: IEC 112, 132 and 160 B5 frames, B5/B14.

The point to note when reading this list is that the power ranges of consecutive housings deliberately overlap. For example, a 0.75 kW motor can be mounted to a HEM50 (0.18-0.75 kW), a HEM63 (0.37-1.5 kW) and even a HEM75 (0.75-3 kW) housing. Which housing you should choose depends not only on power but on the output torque and reduction ratio you want. If you need a high ratio (for example 1/80, 1/100) and high output torque, selecting the next housing size up at the same power is safer for both gear life and heat management. For this reason, the answer to "how many kW of motor fits" is often not a single housing but a range that becomes clear according to the application.

As you can see, as the housing grows, the carried power and IEC frame size increase together. For example, the HEM30 worm gear reducer works at the smallest powers (0.06-0.18 kW), while the HEM130 worm gear reducer goes up to the 4-11 kW range. At intermediate powers more than one housing may be compatible; in that case, selecting the larger housing according to your load and continuity conditions extends both motor and gear life.

HEM worm gear reducer housings and compatible IEC motor frame sizes table

NMRV Market Equivalent: Which NMRV Does a HEM Housing Match?

In the market, worm gear reducers are mostly referred to by the NMRV housing designation. If you have an NMRV housing number in hand, you can match the HEM equivalent with this logic: the housing center distance (mm) is the basis of the numbering, and the HEM series overlaps exactly with NMRV dimensions.

  • NMRV30 = HEM30
  • NMRV40 = HEM40
  • NMRV50 = HEM50
  • NMRV63 = HEM63
  • NMRV75 = HEM75
  • NMRV90 = HEM90
  • NMRV110 = HEM110
  • NMRV130 / NMRV150 = HEM130

So if you are asking "which motor fits an NMRV63 reducer?", the answer is the values in the HEM63 row: between 0.37 and 1.5 kW, IEC 71/80/90 frame, B5 or B14 flange. Thanks to this matching, you can comfortably choose a suitable HEM motor for a reducer of another brand as well.

The NMRV designation is so widespread in the Turkiye market that most machine builders specify the reducer directly by its NMRV housing number on their technical drawings. If you see an expression like NMRV63 or NMRV75 on the assembly drawing in front of you, the matching table above lets you find the HEM equivalent and comfortably choose the right motor. This is especially useful when you are looking for a spare motor for a line installed years ago: whatever the reducer brand, because the housing center distance is standard, the HEM motor fits exactly.

B5 or B14? Why Is Flange Compatibility Critical?

For the motor to seat onto the reducer input, the flange type must match. There are two types:

  • B5 (large flange): The large flange on the front cover is connected with through-holes and bolts. It is preferred in larger-diameter, high-torque connections.
  • B14 (small flange): Connected directly through threaded holes on the front face. It is more compact and common on smaller frames.

The same IEC frame size may exist in both B5 and B14 versions; however, whichever type the reducer input is bored for, the motor must be in that flange. A B14 motor cannot be fitted to a reducer with a B5 bore. If you want to examine the differences between flange and connection types in depth, you can take a look at our B5 or B14 flange selection guide.

Output Speed and Reduction Ratio: Determine the Motor Speed Correctly

The speed of the motor you attach to the reducer directly determines the output speed. In HEM worm gear reducers, single-stage reduction ratios are offered as 1/7.5 - 1/10 - 1/15 - 1/20 - 1/25 - 1/30 - 1/40 - 1/50 - 1/60 - 1/80 - 1/100. To find the output speed, it is enough to divide the motor speed by the ratio:

  • 1400 rpm motor + 1/10 ratio -> approximately 140 rpm output
  • 1400 rpm motor + 1/30 ratio -> approximately 46 rpm output
  • 1400 rpm motor + 1/50 ratio -> approximately 28 rpm output
  • 1400 rpm motor + 1/100 ratio -> approximately 14 rpm output

That is why, when ordering a reducer, you need to clarify not only "which motor fits" but also "which output speed do I want". The most frequently preferred ratios are 1/10, 1/20 and 1/30; they are chosen according to the output speed the application requires. If you need a very low speed (for example a few revolutions per minute), a high-ratio reducer and a small low-power motor to suit it; if you want high torque and medium speed, a larger housing and a more powerful motor are required. If you are undecided about speed and power combinations, our power and speed options content will guide you.

Do Not Confuse the Motor Frame Size with the Reducer Housing

In the field, the greatest confusion arises from the two different meanings of the word "housing/frame". In the reducer, the housing is the size of the reducer body such as HEM30/HEM63/HEM130. In the motor, the frame is the build size of the motor such as IEC 56/63/71/80/90/100/112/132/160 (frame size). One HEM housing accepts certain IEC motor frames. For example, the HEM110 reducer accepts IEC 100, 112 and 132 motor frames. When ordering, specify both separately: such as "HEM110 reducer, IEC 112 B5 flanged, 4 kW, 1400 rpm motor". This clarity largely prevents the wrong motor from arriving. For details on motor frame size and power matching, our article on frame size and power matching will be useful.

Efficiency Class and Copper Winding: Important in a Reducer Motor Too

Since a motor mounted to a reducer generally runs continuously, the efficiency class (IE3/IE4) and winding quality directly affect operating cost. HEM reducer motors are produced with 100% copper winding; this reduces heating and extends life. By regulation, IE3 is already mandatory at certain powers; we detailed this subject in our IE3 stock guide. When choosing your reducer motor, by also taking the efficiency class into account, you can make a choice that is both compliant with the regulation and economical.

Which Motor Should You Choose for a Reducer?

The frame material also matters in a motor that will be mounted to a reducer. At small and medium powers, aluminium-frame motors (0.12-2.2 kW) are light and economical; for heavy duty, high power and harsh environments, a cast iron frame is preferred. HEM's electric motors for reducers series is produced exactly for this purpose, in IE3 and IE4 efficiency classes, with 100% copper winding. If you are wondering whether you should buy the reducer and motor separately or as a monoblock unit, our article on geared motor or separate motor + reducer helps you decide.

To see the wider reducer family and housing options, you can review our worm gear reducers category. If you want to compare with helical-bevel solutions, our K series helical-bevel or worm gear comparison will serve you.

Frequently Asked Questions

Which motor fits an NMRV reducer?

Match the NMRV housing number to its HEM equivalent (for example NMRV63 = HEM63), then choose a B5 or B14 flanged motor suitable for that housing's kW range and IEC connection options. In the NMRV63 example, that is a motor of 0.37-1.5 kW, IEC 71/80/90 frame, B5 or B14 flange. You only need to confirm the reducer input's flange type (B5 or B14) and the input speed (usually 1400-1500 rpm).

Can a B14 flanged motor be fitted in place of a B5?

No. The hole pattern and diameter of B5 and B14 flanges differ; whichever type the reducer input is bored for, the motor flange must be the same type. Even though both B5 and B14 motors exist in the same IEC frame size (for example frame 80), they cannot be used in place of one another. Confirm the reducer's input flange before ordering; if you are not sure, send us the reducer housing number and we will match the motor in the correct flange.

If more than one kW motor fits my reducer housing, which should I choose?

Most HEM housings have a power range (for example 0.75-3 kW for HEM75). For light, intermittent loads choose a power close to the lower limit; for continuous and heavy loads choose one close to the upper limit. If you tell us your output torque and speed requirement, we recommend both the right power and the suitable reduction ratio together; this way neither the motor is strained nor the gear life shortened.

How many poles (what speed) should the motor I mount to the reducer have?

In standard worm gear applications, a 4-pole, 1400-1500 rpm motor is used and the reduction ratio is selected accordingly. A 2-pole (2800-3000 rpm) motor gives roughly twice the output speed at the same ratio and is generally not recommended for worm gears, because heating and efficiency loss increase. If lower speed and higher torque are desired, a 6-pole (900-1000 rpm) motor can also be selected. Tell us your output speed target; let us determine the right pole-count and reduction-ratio combination together.

Get a Quote

Send us your reducer housing (HEM or NMRV number), the output speed you want and the flange type; let us quickly match a motor that fits you exactly from our Turkiye stock and present a quote. With manufacturer assurance since 1979, you source both the reducer and the motor under one roof. Call our line at +90 (532) 345 49 86 right away, or reach us through our contact us page; let us make the right housing-motor match together.