Mixed standards can be a threat to almost any industrial application, particularly in an operation that is global and sourcing parts from numerous worldwide suppliers. One of the most significant and most pernicious examples is the difference between NEMA and IEC electric motor standards. While the two standards are similar, they are different enough to cause substantial problems in applications where NEMA and IEC motors are being mixed-and-matched.
The two standards have differences in mounting types, sizes, weights, and builds. These differences can significantly impact your engineering decisions, especially if you have to replace a NEMA motor with an IEC “equivalent” or vice-versa.
So, in this article, we’ll cover the major differences between the two standards. Of course, if you ever have questions or need assistance making a transition between motor types, contact Wolters Motors for help.
The biggest single difference between the two standards is their area of origin.
The National Electrical Manufacturer’s Association (NEMA) standard applies primarily to motors manufactured in North America, particularly the USA. They also see significant use in South America and other countries, with the US as a major manufacturing trading partner.
The International Electrotechnical Commission (IEC), on the other hand, is based in Europe and is the more common of the two standards. An estimated 70% of motors sold worldwide are IEC motors. This makes IEC the ‘default’ in many applications, except those solely in the Americas.
The first practical difference between the two motor types is units; Imperial vs Metric. NEMA still utilizes imperial units, while IEC is standardized on metric units. This difference can make it difficult to properly mix and match motor types without a lot of double-checking of measurement conversions.
It’s also worth mentioning that motor manufacturers – especially those in the Americas – will produce motors to both standards. Sometimes they have the same components in different motors, even if the standards vary. This can make it easier to swap between them, but it will never be a fully seamless change.
Now, let’s dig a little deeper. For clarity, this discussion will be focusing on low-voltage motors, less than 600V, in the 1-350HP range. These are the most common in typical applications.
As mentioned above, the biggest physical difference between the two motor standards is imperial vs metric units. However, there are significant differences in terms of mechanical construction as well. In some cases, particular designs may only be available in one type but not the other.
For example, NEMA standards include niche case designs, such as motors proofed against open drips. These can be useful in compressor and fan applications, and it can be difficult to find IEC equivalents.
Some of the other major differences include:
The materials used in construction can vary between standards. IEC motors are typically made of aluminum or cast iron, while NEMA motors use rolled steel or cast iron
This variation is also true of the lubricants used. IEC standards typically call for lithium grease, while NEMA uses polyurea-based greases. These lubricants are not equivalent, which can cause significant issues in applications where both motor types are in use. Each motor must receive the appropriate lubrication for its type, or it may quickly break down.
There are also likely minor but critical differences in construction, such as the spacing of mounting holes and differing shaft lengths or heights.
In addition, the conduit box will be in a different position. NEMA typically uses a side-mounted box with direct leads for connections. Most IEC motors put the conduit box on top, with a separate terminal block for making connections.
In addition, NEMA motors frequently feature a small hole at the bottom (often called a ‘weep hole’) specifically for condensation to drain out of the motor. NEMA severe duty motors will have a shielded breather drain for the same purpose. Most IEC motors do not have this feature, which may be an issue for high-humidity applications.
IEC motors favor having sealed shafts, typically using a standard lip seal, even in standard-duty motors. Seals are much less common with NEMA motors except in severe duty motors.
As an aside, “severe duty” is not a defined standard, so research is called for when implementing these in a mission-critical application. Even within NEMA or IEC standards, severe duty motors can vary significantly in construction or specifications.
Because American and European countries utilize different power systems, there are significant electrical differences between the two motor types.
North American NEMA motors are typically 3-phase and 60hz and usually run at 230/460V. . IEC motors use the American 3 phase, 60Hz, 230/460V, but also rate frequently to the rest of the world standard, 50Hz, and many other worldwide voltage standards
There’s also a significant difference in the tolerances, with NEMA typically allowing for higher tolerances. NEMA motors must keep voltage fluctuation at ±10% of the rated amount while within ±5% of the rated frequency. On the other hand, IEC motors separate their motors into ‘zones’ depending on usage. Zone A motors are only allowed ±5% voltage variation and ±2% frequency variation. IEC Zone B is closer to NEMA standards, with ±10% voltage variation and frequency variation of +3% or -5%.
Duty cycle loads vary between the two standards as well. NEMA classifications are relatively simple, with a continuous duty cycle rating and defining intermittent duty motors based on 15-, 30-, or 60-minute cycles. IEC cycle standards are more granular, with ten different standards depending on usage cycles.
It’s worth mentioning that temperature and pressure standards are largely the same and shouldn’t affect electrical decisions. They both standardize on a 40°C (104°F) maximum temperature and minimum temperatures of -15°C (5°F). Likewise, pressure ratings based on altitude are the same: 1,000 meters (3,000 feet) above sea level.
Finally, there’s the matter of electrical efficiency. NEMA only has two efficiency standards defined in the document MG 1. These are “Energy Efficient” and “Premium Efficient.” The latter is a trademarked term used by manufacturers paying to be part of NEMA’s premium motors program.
In IEC terms, these are largely equivalent to IEC IE2 and IEC IE3, respectively.
In addition, the Department of Energy (DoE) regulates motor energy efficiency in the US, with mandated efficiency levels for all motors sold in the US. Canada has also adopted these regulations, and Mexico largely follows them.
Whereas in Europe, the regulations are more relaxed. IE3 motors are often required, but motors with a variable-speed drive can use IE2.
Also, while a niche application, the two standards handle fire pump motors differently. NEMA and DoE standards consider them separate cases, exempt from typical energy standards. IEC draws no such distinction and holds fire pump motors to the same standard as other motors.
In short, running an operation with a mix of IEC and NEMA motors will be a challenge. When maintaining equipment that already has mixed motors, take care to maintain them at their respective standards. As mentioned above, the matter of lubrication is particularly crucial. Using the wrong lubricant with either type of motor can quickly lead to problems.
Should the situation arise where you need to replace a motor and may have to switch between standards, contending with physical and electrical differences is guaranteed. You will move mounting holes. The machinery may need reconfiguring to accommodate physical differences, such as repositioned conduit boxes.
High voltage motors may need electrical adapters. In rare situations, voltage or frequency tolerances could be an issue, particularly if existing NEMA systems have to power a relatively intolerant IEC motor.
Research and thought will be required whenever doing such swaps.
Since 1968, we’ve been one of the premier distributors of motors, power transmission systems, and associated components across North America – and the world. We have an extensive stock of both NEMA and IEC motors and the expertise to help you integrate them into your existing applications.
If you’re having difficulty managing mixed motor types, please contact us for advice and help.
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