Specifying Molded Case Breaker

[tin2779]

Hi,

I have done it quite a few times but now I have an application where I have to go into a bit of detail for specifying a circuit breaker.

I know that if I have to operate a molded case breaker or for that matter any type of circuit breaker remotely or external means, I need a shunt trip coil.

|---||-----(TC)--|

The above normally open contact is a push button located remotely that will open the breaker.

What would make me ask for a auxillary contact.
In the situation below and above what is the difference:

| 52A
|---||---||--(TC)--|
|

I would appreciate, if you could advise, what am I missing conceptually here.

Thanks

 

[tin2779]

Sorry about interjecting in to my own question, I found some thing on this link below on Page10 of 23

http://downloads.eatoncanada.ca/dow...uide/Series C MCCB Internal Accessories_s.pdf

Here a shunt trip is represented as
a
|--||--(ST)---|

Should I presume that when a shunt trip is used, A contact with designation "a" similar to circuit breaker auxillary contacts comes with it. As far my understanding goes, this contact opens as breaker opens and removes power to shunt trip coil, which removes coil to tripping coil(Shunt trip coil) of molded case breaker.
Please correct me, I think the same concept works with Med. voltage breakers as well.
This thing is confusing me.
I would appreciate a help.

 

[alehman]

Shunt trip coils are frequently designed for intermittent duty only. The idea is to remove the voltage from the coil as soon as the breaker opens, so as not to cause it to overheat and burn out.

 

[davidbeach]

As alehman said. Plus, as you get into bigger breakers, MV and higher, the trip coil current is very difficult for the relay contacts to interrupt. So the conventional solution is that the relay trips the breaker and the aux contacts on the breaker interrupt the trip circuit when the breaker opens. Following that the relay can open its output contact without the need to interrupt the current of the trip coil. Same with close coils.

 

[alehman]

And they will burn out, as I've determined through actual field testing . They make lots of really stinky smoke which is also good for testing fire alarm systems.