When selecting operator controls and pushbuttons, you must choose those that are rated for the environment in which they will be used. Will they be exposed to circulating dust, dripping liquids, freezing temperatures? Are they in a washdown area or in an environment that is highly corrosive? Standards developed by the International Electrotechnical Commission (IEC) and by the National Electrical Manufacturers Association (NEMA) assign ratings to pushbuttons and controllers according to how impervious they are to personnel contact and to the ingress of dust and liquids. This article discusses the various ratings and highlights some of the features that protect a controller from water, oil, and dust. NEMA ratings for 30.5 mm pushbuttons and indicator lights. 30.5 mm heavy duty, watertight and oiltight pushbuttons and indicator lights are available in momentary, push-pull, and switch selector models. There are also joystick and roto-push models. These controllers meet NEMA ratings 1, 2, 3, 3R, 3S, 4, 4X, 12, and 13. Contact a group like Flodyne Incorporated to get an idea of what is available. Levels 1 and 2 are for indoor equipment, and as in all of the NEMA ratings, indicate that the controller will protect personnel from incidental contact with enclosed equipment. 3, 3R, and 3S are for indoor or outdoor operation, with 3 also providing windblown dust protection. NEMA 3 and 3R rated controllers are not damaged by external ice formation, while NEMA 3S means external components are still operable when there is external ice formation. NEMA levels 4 and 4X are indoor/outdoor rated. NEMA 4 controllers are protected from wind blown dust and rain, splashing water and hose directed water. NEMA 4X also protects against corrosion. Both 4 and 4X ratings mean there will be no damage from external ice formation. (This rating does not mean the internal components are protected from internal condensation or icing, however). NEMA 12 is an indoor rated controller protected from falling dirt, dust, lint, and fibers as well as dripping and light splashing of liquids. NEMA 13 is an indoor rating the same as 12 except with the added protection from spray, splash, or seepage of water, oil, or non-corrosive coolants. International Protective Marking, or IPM ratings. The IP, or Ingress Protection ratings, made standard by the IEC are similar to the NEMA ratings but are written in code. There are basically two numbers in an IP code as it relates to pushbuttons and other operator controls. The first number rates the protection from personnel access to enclosed parts and the protection from infiltration of solid foreign objects. In this scheme, a first digit of 0 means there is no protection while a 6 indicates the controller is dust tight with no access...