An electrical switching device that in it's normal rest state does not conduct an electrical current. To become conductive an external force must be applied to change, (switch), it's physical state from open to closed.
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A normally open switch is a type of switch that the connection is not made until you push a button; when the button is released, the connection is broken. A normally closed switch is when a connection is made whenever the button is not pushed, and then the connection is broken when the button is pushed. Open=not connected; Closed = connected.
Normally open contact of a contactor or relay become close when the contactor or relay energized its roll like a door which open and close with the operating of its coil energized
It is a contact block with three poles. Pole one is normally open, pole two is normally closed and pole three is normally open. These reading are taken in a de-energized condition. When energized the contacts will change status to closed, open and closed.
Use a normally closed (NC) contact switch rather than a normally open (NO) momentary contact switch.
A relay is an electrical switch. It consists of a electromagnetic coil and a set of mechanical contacts. Depending on the relay their could be multiple sets of mechanical contacts. The close contact lets current flow through the mechanical contacts when the relay is not turned on. When the relay is turned on current flow is stopped. This is called a normally closed contact or NC The open contact works the opposite of the closed and is referred to as a normally open contact or NO
An N.C. contact is 'Normally closed'. This applies to relays (electronic switches). You can use either a normally closedcontact or a normally open contact to do what you need, provided the relay has both and depending on your situation. Here's a recent example of mine: A building's fire alarm is wired to the HVAC system to shut down ventilation in case of a fire. In this case we want the HVAC to have power normally but remove power (with the relay) during a fire alarm. We would connect the HVAC power to the relay's N.C. (normally closed) contacts, because they are exactly that: normally closed. This would allow the HVAC to function. When power is applied to the relay, it would switch contacts, disconnecting power to the HVAC. An important note is that contacts and other electrical connections that can change condition (such as a relay) are described in a de-energizedstate. Thus, the N.C. contacts are normally closed, while the power to the relay is off. Likewise, a N.O. contact is open with relay de-energized but will close upon supplying power to the relay.
It depends on the phototransistor's design. Most are normally open until you shine light on them.