IEEE 841 motors, sometimes referred to as NEMA Premium, are the globally accepted standard for motors being uses in the most extreme conditions. The IEEE 841-2009 standard, which addresses “premium efficiency, severe duty, totally enclosed fan-cooled (TEFC), squirrel-cage induction motors — up to and including 370 KW (500 hp),” is often used as a benchmark. This standard was written for the chemical and petroleum industries. This means many of the design specifications are meant for motors that are being used with pumps, fans, and blowers because these are the common type of applications used in the chemical and petroleum industries.
According to the IEEE 841 standard, severe duty motors are used in the following service conditions:
- Ambient temperatures from -25° C to 40° C (-13° F to 104° F)
- Altitude to 1000 m (3281 ft)
- Humid, corrosive, or salty environments
- Full voltage starting
- Class I, Division 2: explosive gas or vapor present during abnormal operation, but not likely to exist under normal operating conditions
These motors are typically made of cast iron, with a beefed up frame to resist vibration, and painted with corrosive resistant paint so that the motor can withstand the rugged environment it is in. The Drive and opposite shaft ends have improved seals (ex. V-ring slingers). When comparing an IEEE 841 to a standard TEFC motor it typically looks like this:
|Junction Box||Die Cast Aluminum or Steel||Cast Iron|
|Fan Cover||Plastic||Cast Iron|
|Lead Seal Gasket||O Ring||Neoprene Boot|
|Shaft Seal||O Ring||V-Ring on Both Ends|
|Bearing Inner Cap||None||Cast Iron|
|Vibration||0.15 IPS||0.08 IPS|
|Warranty||18 Months||5 Years|
Why Upgrade to an IEEE 841 Motor?
Standard TEFC’s have weaknesses, like their seals. If there is any amount of airborne contaminants or extreme amount of mechanical stress it is likely that a standard motor will fail before its expected lifetime. Bearing failures, due to contamination, are the number one cause of motor failures. If the upgrades that IEEE 841 motors have do increase life expectancy why don’t all motors have them? The simple answer is cost. Most standard TEFC motors are designed to minimize costs while still meeting NEMA MG1 regulations.
Based on experience, it is common for industrial facilities to have at least one, usually more, standard duty motors installed in a severe environment application. Knowing this, the question becomes how long is a TEFC motor lasting between repair and replacement? The average data says that you should expect around a 10% price increase, in most cases that price increase is less than the internal costs to remove, replace, and re-install a new motor – one time. Not to mention that an IEEE 841 motor has a standard warranty of 5 years.
Identifying and Prioritizing Upgrades
The easiest and least risky way to identify and plan upgrades is to thin slice your way to the most immediate opportunities. To do this you need to ask yourself and answer a few questions;
1) What motors fail the most?
2) Are motors failing before their life expectancy?
3) What is the cause of failure?
4) What are the most critical motors in operation?
5) Would it help to increase their life expectancy?
By asking yourself and answering the questions above you should have a good grasp on what motors should be upgraded and have a firm foundation for planning.