Understanding Motor Nameplates Weg, Marathon, Leeson, IronHorse from AutomationDirect
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(VID-MT-0013)
This video provides the details needed to buy a replacement motor. AutomationDirect sells an incredible selection of motors from a wide range of brands to fit most any application.
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AutomationDirect sells an incredible selection of motors from a wide range of brands to fit most any application. A motor namplate can tell us a lot about our motor and provide the best information to find a replacement. Most motors sold in North America are built and labeled according to NEMA standards. NEMA does indicate some of the data that is shown on the nameplate but there are a lot of ways it can be displayed and each motor manufacturer seems to have their own format. We’ll find the motor manufacturer, part number, serial number, etc. Since we’re focusing on what we need to shop for a motor, we won’t get into the details of everything on the nameplate in this video. If you’d like to see a detailed video on these other items, please comment below and we’ll see about putting that together. So, let's get into what is likely the most important data to most people on the nameplate. We can see this motor was designed for 60hz, 3-phase operation. Then, there’s horsepower, operating voltage and current. It’s fairly typical for 3-phase motors to operate at either 230 or 460 volts and single-phase motors at 120 or 240 volts. Keep in mind these are nominal voltages and your system might be 115, 240, or 480 volts and that’s fine. If you have 208 volts this may also be shown on the nameplate, or you may need to check the motor specs to verify it’s rated for this voltage. You’ll also notice current listed here. There is a slash between the 2 current numbers, just like between the voltages. That indicates these numbers are matched to the voltages. So this motor will draw 2.94 amps at 230 volts and 1.47 amps at 460 volts. These current ratings are always full load amps or FLA. This particular motor shows 50hz alternate data. Most 3-phase motors will work fine on 50hz or 60hz. The nameplate may indicate this and show the available voltages, the full load amps and the speed for 50hz. Be aware that some motors may have a lower HP rating when used with 50hz. It's less common that a single-phase motor can operate at 50hz so be sure to check the nameplate or the specs. Speed is always shown as RPM. At 60hz, a 2-pole motor would have a synchronous speed of 3600 RPM, a 4-pole would be 1800 RPM and a 6-pole motor would have 1200 RPM. You’ll notice on this nameplate the speed does not match any of these. This is because motors must have slip to create torque so this motor indicating 1765 RPM tells us we are looking at slip speed, which is listed at full load. A typical 4-pole motor with an 1800 RPM synchronous speed will generally have a full load or slip speed in the range of 1725 to 1785. Then we have frame. Frame specifications are standard across all NEMA motors and tell us a great deal about some physical attributes of the motor. If the frame number has 3 digits like this one, we can take the first 2 digits and divide by 4 and determine the height from the base to the center of the shaft in inches. If the frame has 2 digits, like say a 56 frame motor, we can divide those 2 numbers by 16 to get the shaft center height. So if you see a 182 and a 184 motor, you know the shaft center height is the same on these since we only consider the first 2 digits. These frame numbers also specify the mounting dimensions and the shaft size, but there’s no neat trick to determine those – you have to look those up in the specs or reference chart. But what that means is, you know that the same frame motor from any number of manufacturers will have the same mounting dimensions and shaft diameter. Of course, there are exceptions that I’ll cover in a minute. After the 2 or 3 digits there may be letters. The most common is C which indicates a C-face. It is often used for gearbox or other load mounting. If you happen to see a U, that is the pre-1964 dimension which will likely be on a quite old motor and you’ll have to compare mounting dimensions to a modern motor to verify you can make it work. J is only used on 56 frame motors and indicates a special threaded shaft designed for a jet pump and a C-face. Watch out for Y or Z designations since Y indicates a special or custom mounting and Z designates special or custom shaft. You may be able to use a standard motor in place of a Y motor by creating a mounting option that can work for you, but a special shaft is often very difficult to match to a standard motor. So for Y or Z frames, you may need to stick with the OEM. So if you’re shopping for a replacement motor, match the voltage, speed, horsepower, and frame and you should be good to go. Motors are typically in stock here at AutomationDirect or the vendor for 2-day delivery. Automation Direct is providing the products and support you need to make us your common sense way to buy industrial controls and motors To see all motors click here. If you need more help finding a motor see our award winning tech support options here. Click here to subscribe to our YouTube channel for upcoming products and solutions.
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