# Normally open/closed held open/closed



## teufelhounden91 (Jul 8, 2012)

I understand the function of normally open and normally closed contacts and how energizing a coil will change its state, but what is normally open "held closed" and normally closed "held open" all about? I'm not understanding how it works and when you would use either.


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## Black Dog (Oct 16, 2011)

teufelhounden91 said:


> I understand the function of normally open and normally closed contacts and how energizing a coil will change its state, but what is normally open "held closed" and normally closed "held open" all about? I'm not understanding how it works and when you would use either.


Normally open from the shelf of the supply-house.

Normally open when there is no power at the coil.


When power is applied to the coil, Normally open contacts will close and send power to the load, lights for example.

Normally closed from the shelf of the supply-house.

Normally closed when there is no power at the coil.

When power is applied to the coil, Normally closed contacts will open and cut power to the load, lights for example.


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## macmikeman (Jan 23, 2007)

Black Dog said:


> Normally open from the shelf of the supply-house.
> 
> Normally open when there is no power at the coil.
> 
> ...



Harry, I believe the op is asking about latching contacts even though he doesn't know what they are called.


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## dronai (Apr 11, 2011)

Xebo


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## Black Dog (Oct 16, 2011)

macmikeman said:


> Harry, I believe the op is asking about latching contacts even though he doesn't know what they are called.


Ah! then he should read *this...*


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## teufelhounden91 (Jul 8, 2012)

Aha! Thank you...great read! Yes I've heard the term latching contact but didn't know what that was. I'm just starting to delve into learning about motor controls. So limit switches use this terminology as well correct? I was confusing the terminology when applied to a limit switch vs a latching relay.

Limit switches refer more to the arm of the switch being in the held open/held closed right?

Thank you for that link, seriously.


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## Black Dog (Oct 16, 2011)

teufelhounden91 said:


> Aha! Thank you...great read! Yes I've heard the term latching contact but didn't know what that was. I'm just starting to delve into learning about motor controls. So limit switches use this terminology as well correct? I was confusing the terminology when applied to a limit switch vs a latching relay.
> 
> Limit switches refer more to the arm of the switch being in the held open/held closed right?
> 
> Thank you for that link, seriously.


:thumbsup:


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## bobelectric (Feb 24, 2007)

In the Marine Corps, we had what they called "School Circle".


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## Big John (May 23, 2010)

A contactor can be both mechanically or electrically held. A latching contactor is mechanically held. A contactor with a seal-in circuit is electrically held. 

For example, fail-safe circuits are often normally-open electrically held-closed or vise-versa. That way the circuit responds the same way to a deliberate emergency operation as it would to a fault condition that accidentally breaks the circuit.


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## teufelhounden91 (Jul 8, 2012)

Ahh I see. Like a fail-safe breaker on an EM circuit.


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## bill39 (Sep 4, 2009)

A limit switch is often either held open or held closed.

Often times an overtravel switch is held open or closed to make something failsafe.

Example: the limit switch is wired normally open but maybe the cylinder that actuates it is retracted in it's normal condition which closes the switch (therefore it is "normally open held closed".

So it you're looking at the pneumatic diagram or testing things with the machine in it's "normal" position then the limit switch would be closed.

Hope this helps.


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## xpertpc (Oct 11, 2012)

bill39 said:


> Example: the limit switch is wired normally open but maybe the cylinder that actuates it is retracted in it's normal condition which closes the switch (therefore it is "normally open held closed".


I'll go one step further with this example and say that the qualifying term would be "held closed" when the system is in its "de-energized" state.


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## bill39 (Sep 4, 2009)

xpertpc said:


> I'll go one step further with this example and say that the qualifying term would be "held closed" when the system is in its "de-energized" state.


I agree, that is the better way to say it.


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## ScooterMcGavin (Jan 24, 2011)

I'm personally not a fan of using the held terminology when working with control circuits. I think that it just adds to the confusion. I prefer that people understand how the circuit works and just refer to the correct contact that's being used. I find it interesting how many people have such a hard time grasping the concept of "normal". For relays that are on all the time I like to use the term "usually energized" to avoid any confusion on what we're talking about.


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## RIVETER (Sep 26, 2009)

teufelhounden91 said:


> I understand the function of normally open and normally closed contacts and how energizing a coil will change its state, but what is normally open "held closed" and normally closed "held open" all about? I'm not understanding how it works and when you would use either.


Normally closed...or normally open is the state that it is in when there is no external influence on it.


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## RIVETER (Sep 26, 2009)

scameron81 said:


> I'm personally not a fan of using the held terminology when working with control circuits. I think that it just adds to the confusion. I prefer that people understand how the circuit works and just refer to the correct contact that's being used. I find it interesting how many people have such a hard time grasping the concept of "normal". For relays that are on all the time I like to use the term "usually energized" to avoid any confusion on what we're talking about.


If it works for you that is okay but what if the parking lot lights stay on all of the time.


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## vinister (Apr 11, 2012)

There's also what is called a "bi-stable relay"

This works with 2 coils and 2 permanent magnets. Its the same principle as when you hold 2 magnets close together and they repel each other. Basically, the relay doesn't want to stay in the middle, the magnet pushes the contacts in one direction or the other. There are 2 coils, one on each side. If you energize one, you can pull the contacts passed the magnet, and then its kind of 'trapped' on that side. The other coil can pull it back. These are useful because they draw no current in either state, they only draw when they are changing state.

They use a momentary on, momentary off signal for the coil.


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## strawburner (Nov 29, 2014)

vinister said:


> There's also what is called a "bi-stable relay"
> 
> This works with 2 coils and 2 permanent magnets. Its the same principle as when you hold 2 magnets close together and they repel each other. Basically, the relay doesn't want to stay in the middle, the magnet pushes the contacts in one direction or the other. There are 2 coils, one on each side. If you energize one, you can pull the contacts passed the magnet, and then its kind of 'trapped' on that side. The other coil can pull it back. These are useful because they draw no current in either state, they only draw when they are changing state.
> 
> They use a momentary on, momentary off signal for the coil.


Does anybody know if there are some online suppliers that sell a latching relay like this in a 20 amp contact rating. 120 volt coil. DPDT? My supply house can't seem to come find them.


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## macmikeman (Jan 23, 2007)

strawburner said:


> Does anybody know if there are some online suppliers that sell a latching relay like this in a 20 amp contact rating. 120 volt coil. DPDT? My supply house can't seem to come find them.


Probably not in an ice cube style, but certainly they are available as ''dedicated purpose'' relays. A bit larger than the plug in style.


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## xpertpc (Oct 11, 2012)

strawburner said:


> Does anybody know if there are some online suppliers that sell a latching relay like this in a 20 amp contact rating. 120 volt coil. DPDT? My supply house can't seem to come find them.


I don't know if you are gonna find one in the 20 amp range - 16 amp seems to be the max. You may have to slave a power relay or a contactor to get what you want. Kinda defeats the purpose though.

What is your application? maybe someone can come up with a plan.

Grainger's has a single coil @ 16 amps
http://www.grainger.com/product/MAGNECRAFT-Single-Coil-Latching-Relay-6CVU0?functionCode=P2IDP2PCP

and a dual coil @ 5 amps
http://www.grainger.com/product/OMRON-Dual-Coil-Latching-Relay-2W923?functionCode=P2IDP2PCP


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## strawburner (Nov 29, 2014)

When I get back to my computer I will draw up a schematic of my application and post it here and the problem I have if I don't use a latching relay. I am sure somebody here may have some good ideas.


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## Tsmil (Jul 17, 2011)

When dealing with limit switches. I was taught the description was how the switch is positioned while in the home position with power off. For an example, if a machine has a gate and there is a normally open limit switch that must be closed for the machine to operate, then the limit switch would be drawn on the prints and described normally open held closed.


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## macmikeman (Jan 23, 2007)

A proper schematic defines the normal states in a legend off to the side someplace from the drawing.


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## Tsmil (Jul 17, 2011)




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