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What is open and closed? Before we get into what normally open and normally closed are, let's clarify what "open" and "closed" mean. As with so many topics that we try to simplify by associating with something we are familiar with, associating electrical current flow with water flow causes a tremendous amount of misunderstandings. Whereas, we open a water faucet to start water flow, we close an electrical contact to start current flow, and instead of closing a water faucet to stop water flow, we open an electrical contact to stop current flow. IMPORTANT CONCEPT:
Normally open - Is a contact that does not flow current in its normal state. Energizing it and switching it on will close the contact, causing it to allow current flow.
Normally closed - Is a contact that flows current in its normal state. Energizing it and switching it on will open the contact, causing it to not allow current flow. Don't overthink these two concepts. That is all there is to it. Also now is a good time to remind you that this is article is talking about the electrical normally open and normally closed symbols which while may look the same as the ladder logic XIC and XIO instructions, are not the same. Example: Now let's go through a real-world example of normally open and normally closed contacts that we are all familiar with. Rarely are these "familiar" examples good for learning, but a 3 way switch is an excellent example of using normally open and normally closed switches. And maybe we'll clear up a few things for the household electrician or do it yourself. First let's break it down into the basics.
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