NEMA KS 3

Abstract

NEMA Standards Publication KS 3 sets forth, for use by qualified personnel¹, a number of basic procedures that may be used for the inspection and preventive maintenance of switches used in industrial and commercial applications rated up to and including<br> 600 V 50/60 Hz ac or ac/dc. <br><strong>NOTE</strong>&#8212;Consult the manufacturer for other manufacturer-specific ratings. <br>The <em>National Electrical Code</em>&#174; defines several switch types: General Use Switch, Isolating Switch, Motor-Circuit Switch, and Double-Throw Switch. In most cases, a switch is capable of interrupting/disconnecting its rated current at its rated voltage. An<br> Isolating Switch does not have an interrupting rating and is actuated after the circuit has been opened by some other means. A Motor-Circuit Switch is rated in horsepower and is capable of interrupting the maximum overload current of a motor with the<br> same horsepower rating. <br>The methods outlined may be used to verify specific characteristics of a switch that was originally built and tested in compliance with the requirements of NEMA Standards Publication KS 1. These methods are intended for field application and are,<br> therefore, non-destructive in nature. Accordingly, these methods cannot be used to verify all performance capabilities of a switch since verification of some capabilities requires tests of a destructive nature. <br>Many tests, including those of a destructive nature, as defined in KS 1, are performed on representative samples of switches by the manufacturer, as part of a routine program of factory inspection. <br>The KS 3 Standards Publication is not intended, nor is it adequate, to verify proper electrical performance of a switch that has been disassembled, modified, rebuilt, refurbished, or handled in any manner not intended or authorized by the original<br> manufacturer. Such switches should be removed from service. <br>¹ For purposes of these guidelines, a qualified person is one who has skills and knowledge related to the construction and operation of the electrical equipment and installation and has received training to recognize and avoid the hazards involved. In<br> addition, the person is trained: <br>&#8212;and authorized to test, energize, clear, ground, tag, and lockout circuits and equipment in accordance with established safety practices.<br> &#8212;in the proper care and use of protective equipment such as rubber gloves, hard hat, safety glasses or face shields, and flash resistant clothing, in accordance with established safety practices.<br> &#8212;in first aid.