Replacing an IE4 Motor with an Equivalent: Selection and IEC Dimensions

When a motor in your facility fails or you are buying a new IE4 high-efficiency motor to upgrade the efficiency class, the most critical question is: How do I choose the equivalent of the existing motor so it fits the field one-to-one? As important as the correct power and speed is that the motor's mechanical connection dimensions (IEC frame, mounting type, shaft diameter, foot and flange dimensions) match. A wrongly chosen equivalent will not fit the machine in the field even if it looks right on paper. As HEM Motor, a manufacturer and supplier, in this article we explain step by step, from a buyer's perspective, how to make the equivalent selection and IEC connection dimensions when replacing an IE4 motor with an equivalent.

The good news: because electric motors are built to the IEC standard, the frame size, foot and flange dimensions are standard regardless of brand. So with the right information, it is possible to choose a one-to-one compatible IE4 equivalent even if the brand differs. Below we cover how this matching is done.

The Three Pillars of Equivalent Selection: Electrical, Mechanical, Environmental

When replacing a motor with an equivalent, thinking of the matching under three headings makes the job easier.

Electrical match: Power (kW), speed (pole count), voltage and frequency must match. These values are written on the old motor's nameplate; we explained how to read the nameplate in our article on reading the motor nameplate.

Mechanical match: The IEC frame size, mounting type (B3/B5/B14/B35), shaft diameter and length, and foot or flange hole dimensions must match. This is the main focus of this article.

Environmental match: The protection class (IP), insulation class (F/H) and duty type (S1) must suit the application's environment. We also addressed the details of mechanical compatibility when switching to an IE4 motor in our article on mechanical compatibility when switching to IE4.

What Is the IEC Frame Size and Why Is It Decisive?

The IEC frame size expresses the height from the bottom of the feet to the shaft center (shaft axis height) in millimeters. For example, frame 90 means the shaft axis is at a height of 90 mm. The frame size standardizes both the motor's physical size and the foot hole spacings. Two motors of the same frame size sit on the same foot holes even if the brand differs.

There is a general match between frame size and power; for example, a certain power-speed combination is typically produced in a certain frame. However, as the efficiency class rises (from IE3 to IE4), in some cases the same power may come in a larger frame; this is a point to watch during transition. We detailed frame size and power matching in our article on frame size and power matching. Our IE4 motors are offered in a wide range from 0.25 kW – 355 kW, from frame 63 to 355.

Mounting Type: B3, B5, B14 and B35 Matching

The mounting type determines how the motor connects to the machine and is the most common point of error in equivalent selection. The basic types are:

B3 (foot-mounted): The motor is bolted to a base or chassis with the feet under its frame. Suitable for belt-pulley, coupling and reducer connections. Frame types 63 – 355L.

B5 (large flange, footless): The motor connects directly to the machine or reducer via the large flange on the front cover, with flange holes and bolts. Frame types 63 – 355L.

B14 (small flange, footless): Connects directly via the threaded holes on the front flange; common at smaller powers. Frame types 56 – 160L.

B35 (foot + large flange): Has both foot and large flange connection; can be attached to both the chassis and the machine body.

When choosing an equivalent, you cannot fit B14 instead of B5 or B5 instead of B14; the flange diameter and hole layout differ. You can review the differences between mounting types and the right choice on our mounting types product page, and find the decision between B5 and B14 in our article on B5 or B14.

Shaft Diameter and Shaft Length

The shaft diameter is critical for compatibility with the coupling, pulley or reducer input. In the IEC standard, a typical shaft diameter corresponds to each frame size; for example, on frame 90 the shaft diameter is usually 24 mm. However, different shaft diameters can also be produced for special applications. When choosing an equivalent, always check the existing motor's shaft diameter and shaft length, because the coupling or pulley was machined to this dimension.

The key dimension on the shaft is also important for compatibility. A wrong shaft diameter or key dimension causes the coupling and pulley not to fit. We addressed the importance of shaft diameter and key dimensions for correct ordering in our article on shaft diameter and key dimensions. On motors working with a reducer, the shaft and flange must fit the reducer input; we covered this in our article on motor matching for reducers.

Practical Matching: Frame Size and Typical Shaft Diameter

The IEC standard establishes a general relationship between frame size and shaft diameter. Commonly encountered matches in practice are: about 11 mm shaft on frame 63, 14 mm on frame 71, 19 mm on frame 80, 24 mm on frame 90, 28 mm on frames 100 and 112, and around 38 mm on frame 132. On larger frames (160, 180, 200 and above), the shaft diameter also grows step by step. These matches give you a quick idea of the expected shaft diameter even when you only know an old motor's frame size.

Thanks to this standard matching, when the correct frame size is chosen, the shaft diameter, foot hole and flange dimensions also mostly match automatically. Still, because a different shaft diameter or length can be produced for special applications, we recommend confirming the dimension on critical connections. This matching logic also applies when selecting a motor for a reducer; to choose the IEC frame and flange suited to the reducer input, see our article on motor matching for reducers.

Terminal Box and Cable Connection

A detail often skipped in equivalent selection is the position of the terminal box and the cable entry. The terminal box may be on top of or beside the motor; choosing the right position according to your existing installation's cable route prevents cable strain in the field. Also, the cable gland being suitable for the IP protection class preserves the terminal box's protection level. We addressed IP protection and correct gland selection in the terminal box and cable connection in detail in our article on terminal box and cable connection. Specifying the terminal box direction when ordering the equivalent motor speeds up commissioning.

Foot and Flange Dimensions: It Won't Work If the Hole Layout Doesn't Match

On B3 (foot-mounted) motors, the foot hole spacings (longitudinal and transverse distances) are standard by frame size. When choosing an equivalent motor, the new motor's foot holes must be in the same layout as the existing base; otherwise you must drill new holes or use an adapter plate for mounting.

On flanged (B5/B14) motors, the flange diameter, pilot diameter (centering diameter) and bolt hole layout must match. In the IEC standard, a specific flange dimension corresponds to each frame size. Therefore, when the frame size is chosen correctly, the flange dimensions also mostly match automatically. Still, because there may be different flange variants, it is safe to confirm the flange dimension before ordering.

Equivalent Selection When Moving from IE3 to IE4

Equivalent selection is done not only for failure but also to upgrade the efficiency class. When replacing an old IE2 or IE3 motor with IE4, the transition is one-to-one in most cases because the IEC frame and mounting dimensions stay the same. This is the most practical way to raise energy efficiency without mechanical changes. We calculated the gains of replacing an old motor with IE4 in our article on IE4 replacement payback.

However, rarely, for higher efficiency the motor may need to come in a larger frame; in that case the foot or flange dimensions may change. In such a case, by informing you in advance, we help you plan the necessary mechanical adaptation (such as an adapter plate). We compared the investment decision between IE3 and IE4 with payback in our article on IE3 vs IE4.

Finding a Fast Equivalent in an Emergency Failure

When a motor fails on the production line, finding the right equivalent fast directly reduces downtime cost. When you provide the nameplate and connection dimensions, we determine a suitable IE4 equivalent from stock and deliver it in the shortest time. We shared the checklist for finding an emergency replacement motor in our article on emergency replacement motor. We explained the logic of keeping a spare motor for critical lines in our article on critical spare motor list.

Before Ordering an Equivalent: A Matching Checklist

Before ordering an IE4 equivalent, gather this information completely: rated power (kW), speed (rpm) or pole count, rated voltage and frequency, IEC frame size (e.g. 132M), mounting type (B3/B5/B14/B35), shaft diameter and shaft length, foot hole spacings or flange dimensions, protection class (IP), insulation class (F/H) and terminal box direction. Almost all of this information is available on the old motor's nameplate and frame.

When you fill this list completely, we can offer an IE4 equivalent that fits the field one-to-one even if the brand is unknown. You can replace even a motor whose old brand is out of production without issue, because IEC dimensions are standard. We addressed the route to replacing an old brand motor one-to-one in our article on replacing an old brand motor, and preventing the wrong motor in our article on nameplate matching. We also listed what information is needed when requesting a quote in our article on information to give when requesting a quote.

Frequently Asked Questions

Can I replace a different-brand motor with a one-to-one equivalent?

Yes. Because electric motors are built to the IEC standard, the frame size, mounting type, shaft diameter and flange dimensions are standard regardless of brand. When you provide the existing motor's nameplate and connection dimensions, it is possible to choose a one-to-one compatible IE4 equivalent even if the brand differs. What matters is providing the dimensions correctly.

Can I replace a B5 flange motor with B14?

No, it cannot be replaced directly. B5 is a large flange, B14 is a small flange; the flange diameter, pilot diameter and hole layout differ. You must choose the motor type your machine was designed for. In a forced transition, an adapter flange solution can be considered, but the soundest approach is to choose the same mounting type.

Does the motor get physically larger when moving to IE4?

In most cases, an IE4 motor of the same power and speed comes in the same IEC frame as the old motor and fits one-to-one. Rarely, for higher efficiency the motor may come in a larger frame, in which case the foot/flange dimensions may change. We clarify this before ordering and, if necessary, inform you in advance for mechanical adaptation.

Get a Quote

Share the nameplate and connection dimensions of the motor you will replace with us; let us quickly determine the IE4 equivalent that will fit the field one-to-one with the right frame size, mounting type, shaft diameter and flange dimensions. As HEM Motor, a manufacturer and supplier, we offer the right equivalent with stock and lead time. Call us now at +90 (532) 345 49 86 or send your request via our contact page. You can review our full IE4 motor range and product portfolio.