Electric motor nameplates carry essential information that helps you to quickly identify the motor model, performance characteristics, rated limits, and more. This information can be used at a glance to determine if a motor is a good fit for the requirements of a specific application.
When you are replacing or upgrading a motor that has performed well, the most straightforward approach is to match the nameplate information with available options to find the best candidates. At eMotors, we have a cross-reference tool built into our site search function that automatically compares your current motor's details with our extensive database to find the absolute best motor alternatives in seconds.
However, you may want to dig deeper and learn how to match nameplate information from different motors. There are two nameplate standards in widespread use. It's important to understand the differences between them and how to compare them if you would like to have the broadest possible selection of motor replacement choices.
NEMA and IEC Standards
The two most common motor nameplate standards are defined by NEMA (National Electrical Manufacturers' Association) in North America and IEC (International Electrotechnical Commission) for Europe and most of the world. These standards were developed individually in different parts of the world in the early 20th century, creating a standardized set of manufacturing, performance, and safety characteristics for electrical components.
Recently, as globalization brings together supply and demand in different parts of the world, you will often see these two standards side by side on the shelves when you are looking to buy an electric motor. Several countries, including Germany and the UK, have even developed their own standards, although these closely match the original IEC standard with minor differences.
While this variety of standards can confuse, the NEMA and IEC standards are quite similar, sharing critical information about the motor in slightly different ways. Their approach's main difference is that NEMA standards allow for a substantial variation in the value of a specific characteristic. In contrast, IEC standards are more exact and have less built-in tolerance.
For in-depth information on each standard, it is necessary to consult the relevant documentation. In the following sections, we'll highlight the key differences you need to pay attention to.
The motor service factor defines the amount of overload that a motor can sustain for a short period, which may be necessary for highly variable load applications. NEMA power ratings account for a 15% service factor, while IEC defines a series of 10 different 'duty types' that include some aspects of service factor and duty cycle.
Rated Load Current
The rated load current is the current drawn by the motor when operated at the rated load and speed. On NEMA nameplates, this value has a tolerance of +/- 10%, while IEC nameplates are more exact and do not account for tolerances at all.
The rated voltage is the voltage that must be applied to the motor terminals when operating it. Because power supply voltage is typically not precise, the nameplate's rating must account for small variations that can occur without damaging the motor. NEMA nameplate values consider a tolerance of +/- 10%, while IEC nameplates include a tolerance of only +/- 5%.
Locked Rotor Current
The locked rotor current is the current drawn by the motor when full power is applied at the terminals with the rotor stationary. This represents the high inrush current that the motor experiences at start-up and is an essential piece of information for determining the correct settings for your over-current protection device so that it will protect your infrastructure from damage without tripping every time the motor starts.
NEMA standards typically use a series of letters from 'A' to 'V' that each represents a small range of current values to define the locked rotor current. IEC nameplates include information about the locked rotor apparent power in their design letters, without providing a direct way to calculate the exact value.
Design Letters And Torque Profile
Both NEMA and IEC standards use a series of design letters that designate a type of torque-speed profile for a motor. The NEMA letters range from 'A' to 'D,' with 'B' the most common type of motor, while 'C' and 'D' represent higher starting torque motors. Similarly, IEC has design letters (N, Y, NY and HY) that define the motor torque and starting characteristics. IEC's 'N' is similar to NEMA's 'A' and 'B,' but you must consult the relevant standards documentation to compare the exact torque-speed curves if you would like to get a precise understanding.
Ingress protection defines the level of protection that a motor enclosure provides against the entry of different contaminants, such as water and dust. IEC's IP codes are relatively well-known and widely used across all electrical equipment types, and their nameplates are required to show it. NEMA nameplates don't need and sometimes do not provide this information.
Switching between motors with different nameplate standards gives you a more excellent choice when selecting a motor and a competitive edge in today's globalized marketplace. While the IEC and NEMA standards' differences are few, they are important to know about and enable you to make better choices and optimize your operations' performance.