Electrical relay?switch question

[chopped]

Hello, I hope the vast knowledge of the members here can assist me in my search for the electrical part i need.
Im looking for a relay or switch. not sure which it would be called.
I want to have 120 volts input , and that would disconnect another 120 volt circuit.I find some that would complete the connection but hard to find one that would disconnect .
Anyone have any ideas ? like what I should be searching for?
Im thinking about a 15 amp load on the one id want to dis-connect.
Thanks

 

[CNC Dan]

So you want a relay that will turn something off, when it's energized?

Most relays will do this. They have contacts that are normaly open (NO) as well as contacts that are normaly closed(NC). Usualy there are three switched contacts. One is common, and will change which of the other two it is connected to when the relay is energized.

You can easily identify such a realy as it will have five connections. Two for the coil, one common, one NC and one NO.

They will be listed as SPDT:
Single
Pole
Double
Throw
Single pole means that it has only one switched circuit.
Double throw means it can connect the common to one of two other contacts.

 

[MikeInEburg]

Look up Contactor relay. That's what you'll need

 

[chopped]

Thanks for the reply yes Im wanting to have a relay or switch that carrys the black straight through.......BUT when the 120 from another circuit energizes it then the contacts open the black is dis connected. hope this helps. I found this one but it looks to energize the terminals and not dis connect them. Ill check the contractor relay also.
90 341 2 Pole Switching Relay 120 Volt Coil 2PDT 12 Amp Cont 125 Vac | eBay

So you want a relay that will turn something off, when it's energized?

Most relays will do this. They have contacts that are normaly open (NO) as well as contacts that are normaly closed(NC). Usualy there are three switched contacts. One is common, and will change which of the other two it is connected to when the relay is energized.

You can easily identify such a realy as it will have five connections. Two for the coil, one common, one NC and one NO.

They will be listed as SPDT:
Single
Pole
Double
Throw
Single pole means that it has only one switched circuit.
Double throw means it can connect the common to one of two other contacts.

 

[BHD]

a little confusion on what your trying or wanting to do, I think,

what is the application, kind of sounds like your wanting to make an automatic transfer switch type thing,

where two different circuits feed one item, but only one feeds at a time, and when the second one is energized it drops the first,?

~~~~~~~~~~~~~~~~~~~~~

If I am understanding you want a Double Throw contactor and the coil powered by the line that you want to sense the line when energized,

 

[CNC Dan]

Thanks for the reply yes Im wanting to have a relay or switch that carrys the black straight through.......BUT when the 120 from another circuit energizes it then the contacts open the black is dis connected. hope this helps. I found this one but it looks to energize the terminals and not dis connect them. Ill check the contractor relay also.
90 341 2 Pole Switching Relay 120 Volt Coil 2PDT 12 Amp Cont 125 Vac | eBay

That relay should work. See the two tabs in the middle, those go to the coil. And the set of three tabs at each end, those make up the two poles of the relay. Each set of three will have one common, one normaly open and one normaly closed. Use the common and normaly closed contacts (from the same side) and you will have what you want.

 

[chopped]

ill try to further explain. The application is for two seperate heating duct damper motors. One is on the wood furnace and the other is oil furnace.My goal is to have the power when the oil blower comes on to open the oil duct and also to close the wood furnace one.But Id like it to be set up to be able to run both units. So the plan is to use a relay or switch of some sort to run the black wire through, But when the wood blower comes on It would send 120 volts to the relay and that would "break" the black. which would open the wood furnace damper and allow air to blow from both units.
Further ,I think I want a relay that is 'normally close' and the 120 volts would make it 'open.
In your thoughts Dan if you were to use this relay , there would be the 120 volts coming into the relay to 'disconnect the two flow through blacks? Thus making the two center terminals the 120 volt white and black from one source? Id also have the other cicuit that Im looking to break.which terminals would be closed (normal) and then be broken when power was applied to the two center terminals? Thanks hope I ding make it to confusing..

That relay should work. See the two tabs in the middle, those go to the coil. And the set of three tabs at each end, those make up the two poles of the relay. Each set of three will have one common, one normaly open and one normaly closed. Use the common and normaly closed contacts (from the same side) and you will have what you want.

 

[chopped]

I think I understand what you mean now that I look at it further..So the 'coil' 120 goes to the center and then just find two terminals that are normal closed, and when the center is powered then it should open the other two terminals? If I understand ..

 

[jwmorris]

A double throw relay has a NO and NC contact one is in contact with the common at rest ("normal") the other is in contact with the common when the coil is energized.

If you need two sets of switches like this, say to reverse a DC motor, you would get a double pole double throw (DPDT).

 

[CNC Dan]

I think I understand what you mean now that I look at it further..So the 'coil' 120 goes to the center and then just find two terminals that are normal closed, and when the center is powered then it should open the other two terminals? If I understand ..

Yup... that's it.