When to choose a Severe Duty Motor.

A severe duty motor, in short, is an improvement over a standard totally enclosed fan cooled (TEFC) motor.

They are tougher and better suited to an industrial environment. There is no standard specification on what a severe duty motor is, so designs vary. They could be viewed as a step between a full IEEE 841 motor and a standard TEFC.

1. Severe Duty Frame

Severe duty motors are designed for more advanced uses who have greater demands. This model is double drilled for installation flexibility, and the drain ports are at the lowest part of the motor. The foot surface is clean and free of paint, as a machined fit should be.

2. Fan cover and junction box

This severe duty fan shroud is cast iron, as is the junction box. The diagonal cut boxes are easier to get into. The manufacturer extended the grease fitting above the shroud for easier access.

3. Feet

How are severe duty motors and standard TEFC motors different?

When you think severe duty, cast iron comes to mind. These motors are heavier than their counterparts with stamped or rolled steel. There is typically a better paint system and a more resilient frame. Both the drive and opposite shaft ends will have improved seals, such as v ring slingers. A typical comparison may look like this:

Body cell	Standard TEFC	Typ Severe Duty
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 or V ring (drive end)	V rings on both ends
Bearing inner cap	No	Cast iron
Vibration	0.15 IPS	0.08 IPS
Nameplate	Aluminum	Stainless steel
Warranty	18 months	36 months

Why invest in an upgrade to a severe duty motor?

If you have any amount of airborne contamination or undue mechanical stress it is very unlikely that many standard motors will hold up to their expected life. Even though they are much better than ODP (open drip proof motors), standard TEFCs have weaknesses, such as their seals. It is no wonder that bearing failures (due to contamination) are the number one cause of motor failures.

You may be asking, if these upgrades really matter then why don’t all standard motors have them. The answer is simply cost. Most standard TEFCs have been designed to minimize costs while still meeting NEMA MG1. To be fair, the motor manufacturers are driven this way by the market. Experience has proven that there is a market for “the cheapest motor I can get”.

Based on our experience, most industrial facilities have at least a few (if not many) standard duty motors installed in severe environments. Two common causes are:

The motor was purchased as part of an equipment package. Machines and process skids are often shipped from the OEM with the lowest cost possible solution. This is how many standard TEFCs end up where a better motor should be installed.
The motor was previously replaced with a standard TEFC, perhaps during a cost cutting initiative. The problem, of course, is that the purchase price savings are quickly lost to repeat failures.

Could a severe duty motor upgrade save you money?

That depends. If most of your motors are operating in clean environments with little undue mechanical stress you probably would not benefit from a severe duty upgrade. On the other hand, the following conditions would tend to indicate you may have an opportunity:

Motors located outside
Exposure to ash, saw dust, or other similar solids
Exposure to greater mechanical stress, such as surrounding vibration or falling objects

It is very typical to see a standard duty TEFC in these applications. The question becomes, how long are they lasting between repair or replacement?

What is the cost difference in a severe duty motor?

Based on average data, you should expect an increase of 6-8%. In most cases, that will be less than the internal costs to remove and re-install another motor – one time. Considering that you also double your warranty (from 18 months to 36 months) it’s a pretty good deal. Keep in mind that designs, prices, and terms vary between manufacturers.

Siemens is one of few manufacturers that offers a complete line of motors for severe duty and process industrial environments – in low, medium, and high voltage. Siemens builds some of the largest rotating equipment in the world, and is able to invest that experience in their low and medium voltage products. We are a stocking distributor of both the severe duty and IEEE 841 product.

For information on the Siemens Motors, Download the Slection Guide Here.

Identifying and prioritizing severe duty upgrades

There are many ways to identify opportunities. One option is to conduct an installed base evaluation. This will provide a detailed list of all motors in service and the storeroom. Pictures are usually taken of problem areas, such as poor bases, failing equipment, or upgrade opportunities.

Another option is an abbreviated approach where you thin slice your way to the most immediate opportunities. This is an easy and low risk way to identify and plan an upgrade. You will want to be ready to answer a few questions:

What motors seem to fail most often? Are these motors failing prematurely? Why are they failing?
What are the most critical motors in operation? Would it help to increase their operating life? How?

Identifying motors under either of the two questions above will provide a foundation for planning. Share this with you motor shop or motor vendor to begin exploring opportunity to improve. There are also several areas we may be of help, for example we can:

Conduct an extensive IBE and log results in a database for analysis.
Lead fact finding meetings to help identify a short list of motors to work with.
Develop motor specifications for purchasing.
Establish multi-year migration plans with contract pricing.