A sweeping change took place on October 24, 1997 affecting nearly anyone that buys, sells, specifies or manufactures electric motors for industrial use in the United States. That was the day the motor efficiency mandates set forth in the U.S. Energy Policy Act (EPACT) took the force of law. The government mandates have created a new definition for the term "general purpose" industrial motor.

EPACT covers a wide scope of industrial motors that can be applied for general-purpose use. It applies to three-phase 230/460 VAC motors of 1-200 HP, T frame with three-digit frame numbers, foot-mounted, NEMA Design A or B, rated for continuous duty. Open or enclosed motors are included, as are two-pole, four-pole and six-pole designs (3600, 1800 and 1200 RPM). Imported motors, as well as those manufactured in the United States, are covered. Motors must be tested for efficiency using procedures outlined in Standard 112 Method B of IEEE, the Institute of Electrical and Electronics Engineers.

"EPACT" efficiency levels are based on Table 12-10 published by NEMA, the National Electrical Manufacturers Association, in its MG1-1993 document. These efficiencies are higher than those of most motors previously marketed as "standard-efficiency" general-purpose motors, but generally not higher than the "premium-efficiency" lines offered for years by many manufacturers. (See Figure 1.) In this sense, motors of the "new" efficiencies are not really all that new at all, as the techniques of designing and manufacturing them are well known. The real difference is in how much more widespread their manufacture, availability and required use has become after EPACT. In essence, what was a premium-efficiency motor is now the new "standard."
 

EPACT concentrates on general-purpose motors. Special-purpose or definite-purpose motors that cannot be used in general-purpose applications are considered exempt. In addition, motors requiring special safety approvals, such as explosion-proof motors, are granted a two-year extension beyond the October 24, 1997, dates.Figure 2 helps define what the Department of Energy, which has rulemaking authority over the EPACT law, considers special-purpose and definite-purpose motors.

EPACT’s ramifications for motor users will become ever more apparent in the months ahead. Because the law set a manufacturing cutoff of October 24, many pre-EPACT-efficiency motors will remain "in the supply chain" for months and probably even years to come. In addition, the law does not require any motor user to replace an existing motor with a higher-efficiency model (though in some applications you might want to do so for economic reasons based on energy dollars saved). Similarly, the law makes no reference to the efficiency of used or rewound motors. However, over time, the marketplace may demand proven, higher efficiencies from rewound or otherwise reworked motors.

More options than ever

Forward-looking motor users have for many years been assessing motor purchases and upgrades based on operating efficiency. In many cases, the decision has involved loading numbers into a worksheet similar to that shown in Figure 3. Based on these numbers, many motor buyers have chosen to pay the extra up-front cost to go with premium-efficiency motors. Others found the economic advantage tipped toward the lower up-front cost of a standard-efficiency motor.

This analysis remains valid in the post-EPACT world. Though the overall level of efficiency for general-purpose motors is now raised, there are still premium-efficiency models available from most manufacturers. These offer efficiencies above EPACT mandates, at an additional up-front cost. Whether it’s worth the premium price to go to premium efficiency remains a matter of "working the numbers." Also, customers may continue to buy standard-efficiency, pre-EPACT-manufactured motors (presumably at a lower price than the newer EPACT-efficiency models) as long as they are available.

Another option involves determining whether your application might benefit from a special-purpose motor exempt from EPACT, and perhaps available at a lower cost. For example, four-pole and six-pole motors having Design C torque performance are not subject to EPACT mandates. Yet, in many industrial applications, especially those starting under load, the additional torque these motors supply is a desirable feature. And their "standard" efficiencies may be perfectly adequate for your needs when balanced against the lower up-front cost. Plus, on some direct drive fans or pumps, the higher RPM common on premium-efficiency motors can offset or even reverse the energy savings. For example, on centrifugal loads, the horsepower requirement increases by the cube of the speed, so a small increase in speed will have a correspondingly greater impact on load.

The point is, which motor to use remains in many ways an application-specific decision. And EPACT has not in any way limited the motor buyer’s options. In fact, by increasing the range of efficiency choices, it has expanded the possibilities.

What’s ahead for motors?

Industrial-duty electric motors are, across the board, extremely efficient means of converting raw energy into useful work. The best internal combustion engines are less than half as efficient as most standard-efficiency electric motors. Electric motor users, designers and manufacturers have nothing to be ashamed of. It’s just that there are ways to make what’s good even better. That’s what EPACT is all about, and we can expect growing use and acceptance of higher-efficiency motors in the years to come.

Beyond the EPACT rules currently in force, other energy-saving initiatives may come to pass over time. These could include mandated efficiencies for motors larger than 200 HP, mandates for single-phase motors, and the formal implementation of yet another wave of efficiency mandates for general-purpose motors based on the so-called Design E table of NEMA for "next generation" energy-efficient motors. Figure 4 shows NEMA Design E efficiencies and compares them with the NEMA 12-10 efficiencies that are the basis for EPACT.

Design E motors have quite different characteristics than today’s "EPACT" motors. EPACT motors are very close to standard NEMA Design B motors in basic performance areas such as locked rotor amp draw and torque. Design E standards, on the other hand, allow a great deal higher locked rotor amps (as much as 50% or more above Design B) as a tradeoff for notching efficiency up a step further by reducing rotor resistance. This may require larger motor starters, plus perhaps other modifications to electrical service. With lower rotor resistance also comes lower starting torque, which may make Design E machines unsuitable for some hard-to-start loads.

Heightened energy awareness

Over the past several years, various actions and events have been directed toward increasing motor efficiency. In the 1980s and early 1990s, it was the proliferation of utility rebate programs, some of which continue in force but many of which are being phased out. Today, it is EPACT.

Going forward, however, the focus on saving electrical energy in industry will undoubtedly shift more and more to analyzing the efficiencies in an entire motor-driven system. While motor efficiencies, taken alone, continue to push into the mid 90% area, overall system efficiencies may well be as low as 50% -- the result of oversized, mismatched or inefficient machinery, or poor operating and maintenance procedures. Simply put, the remaining few percentage points of inefficiency that might be wrung from a motor, at considerable additional effort and cost, are dwarfed by the dozens of percentage points of gain possible through a comprehensive systems approach. This is especially true when the system is relatively high horsepower and operates all or most of the time, such as many fans, blowers or pumps. Plus, as we’ve indicated in discussion NEMA Design E motors, further efficiency gains in motors are likely to come only by trading off key performance factors, such as starting amperage and torque.

Very often, the systems approach involves the use of adjustable speed inverter drives to modulate output, rather than simply using single-speed motors and throttling techniques such as valves or dampers. Motor manufacturers have developed new product designs and enhanced manufacturing methods to address the growing application of electric motors with inverter drives. Many of these focus on ensuring that the motors can withstand voltage spikes introduced by transistorized inverters.

LEESON, for example, includes its Inverter Rated Insulation Systems, or IRIS™, as standard on three-phase motors 1 HP and larger – the sizes most likely to be used with inverter drives. This multi-step system involves winding the stator with premium cost, voltage spike-resistant magnet wire, inserting specially formed phase insulation, cushioning and sleeving connections from the leads all the way into the turns, and dipping the wound stator in deep-penetrating, high-temperature varnish.

Applying motors on adjustable speed drives can also sometimes allow the motor to operate at an RPM too slow to move sufficient cooling air over its surface. Constant-speed blowers can solve this problem, and manufacturers now offer these as kits that can convert already installed motors to blower-cooled motors per NEMA MG1.6 (IC46) standards. (See Figure 5.)

In reality, though, adjustable-speed drives are only one important tool in the solution that involves an overall effort to match system performance more closely to process requirements. Already, programs to encourage such "process optimization" through financial assistance have taken root under the auspices of electric utilities and public-private consortiums. Plus, the Department of Energy, through its Motor Challenge program, continues to showcase the advantages of managing all parts of a motor-driven system. This overall systems approach, of which energy-efficient motors play a key role, clearly represents the trend for the energy-aware future.

These guidelines, issued in June as part of a Department of Energy draft, clarify what categories of motors are exempt or covered by EPACT mandates.