Amp Frame / Amp Trip

[Cold Fusion]

(cut) When sizing breakers per the various tables in the NEC do you use the AT or trip rating of a particular breaker to select the correct size? I would not think that you would use the frame rating.

See 240.6(B), and 240.6(C). Generally speaking it is the trip rating

cf

 

[iwire]

(Granted I only deal with substations)

I am willing to bet that has a heck of lot to do with the confusion.

On the prints I see AT is the trip level.

 

[iwire]

If the AT is the trip setting do you go back and change the one line each time a trip setting is changed?

Changing the trip setting is almost never done in normal commercial / residential work below 600 volts.

 

[coulter]

It SHOULD be but I bet it actually is less than 10% of the time...

I can't tell you about others, but I change the one-line any time I change trip setting.

carl

 

[mull982]

I have also seen the terms In and Ir used on types of breakers. I am assuming that In is the frame rating, and Ir is the rating of the trip unit installed.

 

[coulter]

... I am assuming that In is the frame rating, and Ir is the rating of the trip unit installed.

Usually In is the rating plug/sensor Amps, and Ir is the setting. The trip unit generally doesn't even know the frame rating.

Get the book on the cb and trip unit. This will all be in there.

carl

 

[vinod]

Really it was a good explanation from Mr.Jraef

Thanks..

 

[weressl]

Yep, have to agree with the others, you are wrong on this. "AT" does in fact refer specifically to the Amp Trip setting. And by the way, it can be used in referring to either an ELCB or a TMCB, there is no specific delineation in that regard.

And to elaborate a bit more, there is a valid reason to list both values. In a lot of cases there are overlaps in the trip ratings available. For instance, you may need a 250A breaker for something. That could be a 250AF/250AT, or it could be a 400AF/250AT. An engineer may specify a 400AF because he knows that someday, the load may increase to 300A. If a 400AF breaker was specified, only the trip unit or rating plug needs to be changed, or in the case of a basic TM CB, at least the space requirements stay the same and the bus connections don't need changing in the switchboard. Had he specified a 250AF/250AT, upgrading might be a lot more involved if not impossible on a full switchboard.

In my opinion AT refers to the Amp Trip RATING and not to the Setting.

Your proposition only works if the installer used full size feeders tot h e 400AF rating. Otherwise the installer not only have to change the trip but the feeder too. (We often install main feeders for present loading and when expansion occur, we add a parallel cable and change the trip.)

 

[car81]

Can someone explain to me the difference between the circuit breaker sensor and the circuit breaker plug?

 

[weressl]

Can someone explain to me the difference between the circuit breaker sensor and the circuit breaker plug?

The 'sensor' is the interface element that provides the data to be measured in a usable signal format. In that case a more proper description would have been the 'current sensor'. The rating plug is a fixed adjustment of selecting the continous current rating of the circuit breaker.

Example:

You have a 3000AF frame circuit breaker that has current carying components and thermal dissipation capability to carry 3000A continously.
You equip the above breaker with a set of 2000A current sensors, now the same breaker is limited to 2000A.
Now install a 1600A rating plug and your above breaker is now rated ADN limited to carry 1600A contious current.

Nethier the sensor, nor the plug should exceed the hierarchical rating of the preceeding component of breaker-sensor-rating(plug).

 

[weressl]

There are multiple meanings,........

..and what would those multiple meanings be?

 

[templdl]

This is meant to provide a general idea and may not include all of the comments and exception that others may have.
Breakers with frames up to 150 and some up to 225a commonly do not have interchangeable trip units and are purchase with a specific ampere rating. These breakers can be feed in either directing and as such are not marked with line and load.
Breakers frames of 250, 400, 800, 800, etc. Consist of a frame and trip unit.
A breaker frame that is factory assembled with a give rated basic physically thermal magnetic trip unit an then factory sealed is considered to be a breaker with a non-interchangeable trip unit which is often indicated an a drawing as (NIT). This breaker does not need to be marker line and load as it can be feed from either direction. Using a 400a C-H breaker as an example a KDB3400 is a sealed breaker with a KD3400F frame and a KT3400T trip unit.
The same breaker could be assembled with an electronic trip unit with a give set of trip option and it could also be sealed. However a breaker with an electronic trip unit can also be consider as a interchangeable trip unit (IT) because a rating pug can simply be removed and replace with another rating without actually taking the breaker cover off and accessing live parts.
Of course breakers that a supplied from either the factory or assembled the field with a frame and a trip unit are considered to have interchangeable trip units. The frames are marked with line and load. A given frame may have a variety of basic thermal magnetic ratings available. As an example a KD3400F can be ordered and a KT3400T installed in it making it the same as a KDB3400 except that it is not a sealed breaker, can not be reverse feed and is considered and IT breaker.
Breakers that are often illustrated on a drawing as a 600AF 350AT are just that, LD3600F w/ LT3500T. The breaker trip unit could be change to be a 600AT of even to be an electronic trip unit which all of the electronic features that may be available.
It must be pointed out that the 350AT rating is also available with a 400AF breaker such as a KD3400F w/KT350T. Both the LD and the LD can have the same KAIC so the only advantage to the LD is its ability to be retrofitted with a LT3600A trip unit if required.
The last thing to be aware of is a breaker that has an adjustable long time setting such as an adjustable rating plug. As such the breaker must be applied at is frame rating when sizing cable unless the longtime setting can be sealed and not changed.

 

[zog]

And that is all just for MCCB's, draw out breakers (LV and MV), VCB's, GCB's, Ocb's, all different concepts than those small MCCB's, (I dont think I have ever worked on something less than 400A)

 

[iwire]

And that is all just for MCCB's, draw out breakers (LV and MV), VCB's, GCB's, Ocb's, all different concepts than those small MCCB's, (I dont think I have ever worked on something less than 400A)

Which means the work you do represents probably less then 1% of the members here. I am not goofing on you, just pointing out that your point of reference is very skewed. :smile:

 

[zog]

Which means the work you just pointing out that your point of reference is very skewed. :smile:

My wife says the same thing about me

 

[iwire]

My wife says the same thing about me

LMAO. :grin:








Oh wait, my wife thinks the same of me.

 

[peter d]

Oh wait, my wife thinks the same of me.

Wife? What's that?

 

[templdl]

Yes, draw-out breakers, commonly available in 800a -4000a frame sizes, the breakers themselves referred to as insulated case and power circuit breakers, older types may be referred to as air circuit breakers.

The breaker itself is essentially a dumb device and depends upon a set of current sensors (CTs), an electronic trip unit, and a shunt trip to trip the breaker.
The CTs a commonly located outside the breaker around the stationary contact and not in the breaker itself. When the breaker is "racked in" to the stationary contacts a set of secondary contacts plug together first before the breaker is completely racked in.
Also they are often used in compartmentalized assemblies where each breaker is separated from the others by its own metal cubical.
The breaker can not be racked in or out in the closed or energized position.
Because these breakers play a major role in the distribution system they commonly have a lot more bells and whistles so that they can be coordinated with up and down stream devices, the capability of being remotely opened and closes, communications, power monitoring, etc.

 

[kingpb]

..and what would those multiple meanings be?

In accordance with ANSI Y1.1 Abbreviations:

AT can mean airtight, ampere turn, anti-tank, and atomic.

Hence the importance of understanding the context in which the abbreviation is used.

AT = Amp trip is not a standard abbreviation, although commonly understood, but as long as it is defined on a legend sheet for the project, you can use whatever abbreviations you want.

Hope that relieves your anxiety.