METRIC MOTORS
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The influx of foreign equipment during the ‘70’s and ‘80’s have put great numbers of metric motors in plants. As a result of this and the age of these motors, we are seeing inquiries for replacement motors that will match the IEC (International Electrical Commission) standards.

To help identify these motors and make suitable replacements, the following information could be useful.

RATING SYSTEM

One of the first things is that ratings are given in kilowatts (KW) rather than horsepower. The first thing to do is to convert from kilowatts to horsepower. It is important to note that even though KW is an electrical term, in this case it is associated with mechanical output (just as horsepower is in this country). A simple factor will make the conversion. Multiply the KW rating of the motor by 1.34 to get the horsepower of the motor. For example, a 2 KW motor would be equal to approximately 2.7 HP and the closest NEMA equivalent would be 3 HP.

The next item of concern would be the speed of the motor. Generally, somewhere on the nameplate of the foreign motor, you find the speed listed in RPM. The convention in Europe seems to be to show the no load speed of the motor and occasionally, the 50 cycle speed may be shown rather than the 60 cycle speed. The following table shows a crossover from the 50 cycle speeds to the equivalent 60 cycle speeds. In some cases, both the 50 and 60 cycle speeds are shown generally separated with a slash, for example, 1500/1800 RPM. this would be a 4 pole motor that U. S. manufacturers would show nameplated with its full load speed. In this case it might be 1725 to 1760 RPM depending on the size of the motor.

FREQUENCY
POLES 50 HZ SPEEDS (RPM) 60 HZ SPEEDS (RPM)
SYNCHRONOUS FULL LOAD
(Typical)
SYNCHRONOUS FULL LOAD
(Typical)
2 3000 2850 3600 3450
4 1500 1425 1800 1725
6 1000 950 1200 1150
8 750 700 900 850

FAILURE REPLACEMENT

When an IEC (metric) motor fails in service the most practical way to proceed is to attempt to get an exact metric framed replacement motor. Baldor and other manufacturers offer a limited selection of the most popular ratings for direct replacement.

When direct replacements are not available, the following information should be helpful in adapting NEMA frame motors to the metric application.

FRAME SIZE

European frame sizes are handled in a different way from U. S. frame sizes. They are based on the shaft height (equivalent to our “D” dimension) in millimeters. For example, a 112 frame would have a 112 millimeters shaft height. Convert this to inches by dividing 112 by 25.4 to get an equivalent domestic shaft height. In this case, the shaft height of a 112 frame would be slightly over 4.4 inches and the closest NEMA frame motor would be a 180 series frame (182, 184, 182T or 184T) with a shaft height of 4.5 inches. This is true for IEC base mounted motors. In the case of this motor, it would be necessary to make adjustments on the machine that would allow for either using the 180 series frame domestic motor and aligning the shaft height difference or by selecting a 145T or 56 frame motor (3.5" shaft height) and shimming up to get the proper alignment. The bolt pattern on the bases of IEC motors are given as metric dimensions and it is impossible to get complete interchangeability with NEMA frame sizes. However, it is usually possible on foot mounted motors to adapt to domestic frame sizes by drilling new holes or making other accommodation to accept the different footprint of the NEMA frame motor. IEC frame sizes for rigid base motors and the associated metric dimensions are shown on page 25. (Dimensions are in Millimeters — Divide by 25.4 to get inch equivalents.)

FLANGE MOUNTED MOTORS

Flange mounted motors become a real nemesis for conversion. There are two popular face mounting configurations used on the IEC motors. The most popular is the “B5” configuration which is closest to NEMA “D” flange motors. the important thing to note is that with the B5 flange, the clearance holes are in the flange and the threaded holes are in the mating part, such as the pump, gear reducer or machine. The other popular IEC flange is the B14 flange. In this case, the threaded holes are in the face of the motor much the same as the NEMA “C” face motors.

IEC flange mounted motors all have metric rather than inch shaft diameters and where threaded holes are involved, they are metric rather than “inch” threads. To replace metric flange mounted motors, an exact flange mounting equivalent would be necessary unless someone is resourceful enough to make adapter flanges that would convert NEMA “C” face motors to the metric dimensions required. Since this usually is not the case, metric flange mounted motors have to be replaced with metric motors. Page 26 shows typical metric dimensions for B5 and B14 metric motors. Note that dimensions are given in Millimeters.

Baldor is now offering selections of metric, three phase, flange mounted motors. We also stock some permanent magnet DC motors that can be used as replacement units. On a custom basis when reasonable quantities are involved we can build many different metric equivalent motors.

SUMMARY

This information should be useful in your day-to-day dealings in metric replacements.

Click here to view TYPICAL METRIC FOOT MOUNTED DIMENSIONS

Click here to view TYPICAL METRIC FLANGE MOUNTED MOTOR DIMENSIONS




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