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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
What else can I help you with?
What is a nc contact?
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.
Can a short circuit current through a photo cell damage it?
If the photo cell was on during the short circuit then the chances of damage to the photo cell are at a minimum. If the short circuit occurred when the photo cell was operated then yes damage to the internal contacts of the photo cell could have happened. What happens is, the short circuit is downstream from the photo cell and when the contacts of the relay close in the photo cell the dead short is applied to the contact faces of the relay. This is somewhat like striking an arc with a welded with the same results, the contact faces weld close and the circuits breaker trips to open the short circuit. With the pole faces of the photo cell's relay closed it gives the illusion that the photo cell is not operating. The photo cell's circuitry will be working but the relay will not drop the circuit open because of the welded contact in the relay.
How does a contact relay weld?
Too much current cause excessive heat and cuases melting of the relay contacts.
If 120V is present on a120V relay coil what will the voltage reading be across the closed set of relay contacts on a 120V circuit?
0v The relay is designed to act as a switch when voltage is applied across the coil. The contacts open or close but only pass through whatever is connected to those terminals. <<>> When a relay coil is energized the relay's contact change status. The closed set of contacts will open. The 120 volt circuit that is connected will turn off. As to the voltage at the contact terminals, it depends on where you are taking the voltage reading from and to. On the source side of the terminal there will be a reading of 120 volts to neutral or ground. On the other side of the contact terminal there will be zero volts to the neutral or ground. This is because that wire is in series with the load to neutral. A meter reading across the relay terminals will read 120 volts.
What does a normally closed relay do when it is energized?
The term normaly closed means that in its normal state the relay or contact is closed. So when energized it will open and break the circuit.
What does nc and no mean in electrical terms?
nc: Normally Closed (contact is closed when power is not applied) no: Normally Open (contact is open when power is not applied) Applies to a relay ex...: when power is applied to a relay the no(Normally Open contact will close and allow current to flow between two terminals on relay).
How do you built a mains fail alarm?
Use an intermediary relay that is specifically and only connected to a circuit from a two pole breaker in the distribution panel. Through the N.C. contact of the relay connect your DC alarm system. As long as the power is on the relay stays energized and the N.C. contacts stay open. If a power failure occurs the relay will drop out and close the N.C. contacts. This will close the circuit on the alarm system.
What is the application of normally closed relay contact?
There are numerous applications for a normally-closed relay contact. It is used whenever you want to disconnect a circuit when the relay coil is energised.
A device that opens and closes a set of contacts when its coil is energize?
The device is a relay. A relay may have several sets of contacts, or sets of open and closed contacts that "change state" as the coil is energized.Changing state means that the normally open contact will close and the normally closed contact will open when the coil is energized.
What is AC rating DC rating wrt Relay contact or contact of contactor?
The contact rating is normally given in AMPs or HP and refers to the load the "switch" in the relay can handle. The manufacture will specify the relay contact rating in the data sheet. This rating depends on the current being controlled by the relay, the connection type (how the relay is mounted) and the duty. A Normally open relay in pilot duty (clicked closed all day) may be only 10% of the same relay in intermitted contact duty. DC current requires a higher contact rating then AC. For example a relay rated at 1A @ 24vdc should also handle 1A @ 120vac and as the voltage increases the contact rating will lessen.
How a dry contact can break 220V circuit?
The fact that it is a dry contact has nothing to do with the amount of voltage it will handle. Contact voltage capacities are rated by the air space between live parts. The further the space, the higher the voltage will be allowed. What limits the contacts are the amount of current they can conduct. Usually relay contacts have the contact rating printed on the side of the relay enclosure. The terminology of a dry contact is, a contact in another piece of equipment that is used to close a relay in a "hot" complete circuit. e.g. An automatic transfer switch has a dry contact that when it closes on a power failure it closes the circuit for the engine start circuit to start the generator.
What is a nc contact?
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.
How does degauss work?
i think ,crt on which temporary magnetic field temporarily connected to the electrical earth by a relay contact (thats why the dwoning sound comes). Then the magnetic field generated is neutralised through the relay contact. in other words charge accumulated discharges to the earth through the relay contact.
Can a short circuit current through a photo cell damage it?
If the photo cell was on during the short circuit then the chances of damage to the photo cell are at a minimum. If the short circuit occurred when the photo cell was operated then yes damage to the internal contacts of the photo cell could have happened. What happens is, the short circuit is downstream from the photo cell and when the contacts of the relay close in the photo cell the dead short is applied to the contact faces of the relay. This is somewhat like striking an arc with a welded with the same results, the contact faces weld close and the circuits breaker trips to open the short circuit. With the pole faces of the photo cell's relay closed it gives the illusion that the photo cell is not operating. The photo cell's circuitry will be working but the relay will not drop the circuit open because of the welded contact in the relay.
How does a contact relay weld?
Too much current cause excessive heat and cuases melting of the relay contacts.
Where is the cooling fan relay on 99 Hyundai accent?
On the engine compartment there is a fuse and relay box close to the battery
What causes contact chatter in electrical circuit?
Overload can cause contact chatter. Once the contact closes, the voltage in the circuit collapses and that causes the relay to drop out. At this pint the relay energizes, since the voltage is back. This cycle will continue on.
