What is normally closed relay?

What is normally closed relay?

Normally closed relay: Normally closed relays default in the closed position, meaning that the circuit is closed unless otherwise specified. Introducing too much power draws the first circuit away from the second circuit to turn it off.

How does a 120v relay work?

The relay is typically used to start (or slave) a secondary device like a booster or exhaust fan. A 120 VAC coil means that you apply 120 VAC to the coil contacts (black wiring) to energize the relay and close the switched contacts (red wiring).

What is coil voltage in relay?

The Rated Coil Voltage of a relay is the voltage that the relay is supposed to receive in order to be energized. This is the voltage that the relay ideally should receive when you energize it.

What does a coil do in a relay?

A relay is an electrically operated switch. They commonly use an electromagnet (coil) to operate their internal mechanical switching mechanism (contacts). When a relay contact is open, this will switch power ON for a circuit when the coil is activated.

How do you tell if a relay is normally open or closed?

As relay diagrams show, when a relay contact is normally open (NO), there is an open contact when the relay is not energized. When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized.

How do you find the voltage of a coil?

All you have to do is start by dividing the primary volts by the number of primary turns: 120 ÷ 75 = 1.6. Since you know the number of turns in the secondary, you would now multiply the 150 secondary turns by the primary current of 1.6:150 × 1.6 = 240. Now you have determined that the secondary voltage is 240 V.

What happens to the normally closed contacts when a relay coil is energized?

Relays involve two circuits: the energizing circuit and the contact circuit. The coil is on the energizing side; and the relays contacts are on the contact side. When a relays coil is energized, current flow through the coil creates a magnetic field.

How do you calculate coil current in a relay?

Once you have these parameters you simply use the equation current = voltage / resistance (amps = volts / ohms). The relay I am looking at has a 24V coil and it has a resistance of 350 ohms. 24/350=. 07 amps.

What happens when voltage is applied to the coil of the relay?

When voltage is applied to the coil of the relay the internal switch goes to the open position and disconnects the power from the load. It is also called Form B. Check out the picture below to better understand how this process takes place.

How does the NC normally-closed SPST relay work?

The NC Normally-Closed SPST (Single Polse Single Throw) relay has an initial closed circuit state when no current is applied to its internal coil therefore it connects the power to the load (fan, light bulb, etc). When voltage is applied to the coil of the relay the internal switch goes to the open position and disconnects the power from the load.

What is form B in a fan relay?

It is also called Form B. Check out the picture below to better understand how this process takes place. 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 close position and the fan will be switched ON because it is connected to the 220V.