With a normally closed flow switch, current flows when fluid is present. The system detects the interruption immediately. Let's start by taking a look at what we mean by normally open or (NO). The ' a ' contact (normally open contacts) are open when the. This guide explains what normally open (NO) and normally closed (NC) contacts do and how to choose, wire, and test them so doors, drawers, and machines behave safely and predictably. You open a panel or access box, see tiny NO and NC markings by a row of screws, and realize one wrong choice could. Any kind of switch contact can be designed so that the contacts "close" (establish continuity) when actuated, or "open" (interrupt continuity) when actuated. The confusion often comes from reading schematics too quickly.
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