NO normally open relay switch states

NO SPST Normally Open Relay

The NO Normally-Open SPST (Single Pole Single Throw) relay has an opened circuit state when no current is applied to its coil so basically it disconnects the power to the load in the inactive state. When current is applied to its coil the generated magnetic field switches the armature and closes the contact so you can say that it turned ON the load (fan, light bulb, etc). It is also called Form A.

Video presentation of how the Normally Open SPST relay works

Check out the picture below to better understand how this process takes place.

NO normally open relay states

Normally-Open Single Pole Single Throw SPST relay

In figure 1 no DC voltage is applied to points A and B therefore no current flows through the coil of the relay, the contact stays in the opened position and the fan will not be switched ON because it’s disconnected from the 220V.

In figure 2 we apply a DC voltage (let’s say 12V) to the coil (points A and B). Now the coil gets energised and it switches the contact to the closed position and the fan will be switched ON because now current can flow from the 220V.

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