Contactor

Dear Friend,

It's just simple.

NO cotact - Normally Open contact when the contactor is in Deenerdised condition

If contactor Energises NO will turn to NC.

If contactor again Deenergises NC will turn back to NO.

NC cotact - Normally Close contact when the contactor is in Deenerdised condition

If contactor Energises NC will turn to NO.

If contactor Deenergises NO will turn back to NC.

We can use this contact points for various application based on the need of NC or NO

Thanks a lot dear

Just a bit non-technical correction.

NO = Normally open = Contacts open when trip mechanism is un-energised- Becomes NC C (closed) when the trip is energised. _{(N is Normally, so N goes off when energised)}

But the meaning in #1 is clear and otherwise correct (Just cut the N )

In my opinion Mr PWSlack comment is the correct one.

If I can see the sun is it daytime? If I can't see the sun is it nighttime?

If I can see the sun is it daytime? If I can't see the sun is it nighttime?

So much seems to get lost in translation. Is there really a mystery to the meaning of normally?

OMG!!!!

_{Turns computer off and walks away shaking head in sadness.}

Actually lynlynch, you bring up a good point. There is an official definition of "Normal State" when referring to electrical equipment, and it does vary by context; in other words depending on the type of equipment in discussion. The comment from "Guest" in #3 could have made more sense had he/she paid attention to the context of the original poster in that they asked specifically about a Contactor. #3 Guest's response would have been correct if we were discussing a Circuit Breaker.

When u have a contactor and the rated coil(A1 and A2) voltage is say 220v signal.When this energising or signal voltage is applied to the contactor coil,and it is energised,the NC(ie Normally Closed) contact of the contactor will become open,while at thesame time,the other NO(ie Normally Opened) contact will become closed.

If u de-energise the contactor,the reverse or opposite of the above will occure.The NC contact will remain CLOSED while the NO contact will remain OPENED.Know that a contactor when it has not been energised,the NC contact is always closed,while the NO contact is always opened.

The NO and NC contacts are used for control purposes.If same 220v signal of the contactor coil is linked to the input of the NO and 220v thru a different switch is applied to input of NC and the output of NO is connected to a 220v lamp 'A' while the output of NC is connected to a 220v lamp 'B' and the other ends of the lamps are connected to neutral respectively.Now we have two switches,one to supply the contactor coil and the NO contact,while the second switch will supply only the NC contact.

When the NC switch is activated,power(220v) will pass thru the contact and lamp 'B' only will glow,because NC is already closed when coil is not energised.When the contactor coil and NO contact switch is activated,the contactor coil is energised and there is power also at the input of the NO contact.The NO contact will close to supply the lamp 'A',and lamp 'A' will glow,while lamp 'B' which was already glowing earlier will go off,because the NC contact of the contactor will be opened,cutting supply from lamp 'B' as long as the contactor ramain energised.When contactor is de-energised,lamp 'A' goes off while lamp 'B' comes on again.

I hope with the above explanation,u can understand how a contactor works with its NO and NC contacts.

Patrick Whowha

It seems to me that you don't have much experience with contactors. Send me your email address so I can send you some exercises to see how a contactor is working in a system.

My mail is: jalkot@iafrica.com

"Normal" means coil de energized, unless otherwise indicated on schematics.

When de energized, the Normally Open contacs(NO) are open, and the Normally closed (NC) contacts are closed.

If you wanted to turn on a light, or motor,etc. on when the contactor energized, series the hot wire thru the N.O. contact.

Contactor de energized=light off.

Contactor energized=light on.

If you want to turn on a light, etc. when the contactor is not energized, use the N.C contacts.

Simple.

I have experience for discussing NO and NC.

In my understanding until now, if there no is any source or supply (de-energize) the NO contact open and NC contact open. This is based on GE schematic drawing for UV relay. The NC contact is closed when the power is off, and contact NO is open. When the system is energize, the NO contact closed and the NC contact open. Both contacts are used for permissive closed the incoming breaker (we cannot closed the breaker while in service/racking-in position) when there is no voltage at the incoming breaker.

However, my understanding is different with instrument engineer. During the first time implementing the PLC for CWP motors, he took NC contact for tripping the system. This NC contact of aux relay of PLC output is in energize and open during normal operation (his opinion it is NO). By implementing this system, there are several plant trip due to momentary PLC supply loss because of UPS fail and human error when someone were puling out the cable supply of aux relay.

While, 4 previous (without PLC) trains have "NO contact" for tripping CWP motor (most electrical system apply energize to trip except for system which safety is as priority one e.g in boiler system). This sistem more reliable, because never happened 2 trains trip at the same time due to momentary loss supply.

I did not say that one is better than the other either using NO or NC what I have discussed above, but we have to consistent in understanding NO & NC.

I was going to comment on the two terminal contactor......but wht the h---. everyone knows how to run a relay (contactor anyways).