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When project budgets and deadlines are tight, it can be very tempting for an electrical contractor to employ a piece of technology that appears a cinch to generate savings in both areas. After all, coming up with innovative solutions to challenges that leave the customer pleased is the lifeblood of any contractor's business.
But there is another side of the issue — a misapplication of the technology that could create downtime, lost sales and customer frustration. Such a scenario could place a contractor's reputation, and future business, with that customer in jeopardy, despite the good intentions.
Case in point: A well-known, simple and reliable means for disconnecting power to motor loads is the Underwriters Laboratories-listed UL 98 safety switch, but UL 508 manual motor controllers suitable for motor disconnect have gained interest in recent years as a result of changes in the National Electrical Code.
However, with that interest also has come concerns about misapplication of UL 508 motor controller switches, which can result in added cost and time for an electrical contractor to replace it with the correct switch, along with possible customer concerns and questions. While there are few statistics available regarding misapplication of UL 508 products in UL 98 applications, informal surveys suggest that the issue is substantial. One such survey of contractors, consulting engineers and OEMs at a recent Schneider Electric customer event indicated that about 40 percent of attendees had indeed misapplied UL 508 motor controller switches as general use switches.
Thus, understanding the key differences between UL 98 and UL 508 devices, along with correct applications for each, can help ensure an installation that is NEC-compliant. It can also help facilitate further convenience for their industrial customers, and help a contractor be viewed as a solutions provider rather than an equipment installer.
Understanding the basics
There are two general aspects to understand when selecting a disconnect for motor-operated equipment, which include the type of disconnect and its location. A device serving to disconnect a motor in accordance with NEC 430.102(B) must be within sight of the motor, which means that it must be visible and within 50 feet of the motor. The reason is obvious: an operator can turn off the switch quickly if there is a problem with the motor or isolate the motor for maintenance.
The second general requirement is to comply with the permitted motor disconnects as found in NEC 430.109. A UL 508 manual motor controller marked "suitable for motor disconnect" provides a disconnect means for a motor exclusively as permitted in accordance with NEC 430.109(6). Understanding all of the information contained within that statement is critical. There are UL 508 manual motor controllers that are not marked "suitable for motor disconnect" and therefore have not been evaluated to interrupt a motor locked rotor condition safely. Also note that permission to use a UL 508 manual motor controller marked "suitable for motor disconnect" is limited to the motor circuit and is not recognized in any other area of the NEC for other loads, so the UL508 manual motor controller is limited to a motor circuit.
