NEMA KS 3-2023

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 600 V 50/60 Hz AC or AC/DC.

NOTE: Consult the manufacturer for other manufacturer’s specific ratings.

The National Electrical Code® 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 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 same horsepower rating.

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, therefore, nondestructive 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.

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.

This 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 manufacturer. Such switches should be removed from service.