Understanding CB Specs on single line dwgs

[aries]

I'm studying a single line drawing done up a few years ago for an electrical room. There are specifications for breakers called out here that I have not been able to determine the meaning of. I'm hopeful someone here might be willing to help me learn from this.

The drawing calls out a breaker specified as:

1200AF
1000AT-(SKLA12)
65K

The electrical service this breaker is employed on is a 277/480 1200A. I don't follow the spec "1200AF" and "1200AT". What is the difference betwen "AF" and "AT" here?

Also, elsewhere in this drawing is called out another breaker as:

125AT
SEDA

What is "SEDA" type?

The system drawn in this diagram was installed 8 years ago and remains in service. Unfortunately I do not have access to the installation any longer so cannot go compare what was built to what was drawn.

Thanks!

 

[bob]

Check here http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GGLL_en&q=1200AF+and+1200AT

 

[R Bob]

AF=Amp Frame

AT=Amp Trip

I believe SEDA is designating a GE type breaker

 

[aries]

AF=Amp Frame

AT=Amp Trip

I believe SEDA is designating a GE type breaker

Yep.. SEDA was a GE breaker -- eventually found that by more google work.

Now when they call out Amp Trip (AT) does this have any relation to this breaker being a 80% or 100% rated? That is to say if a drawing such as this calls for "1000AT" does it "in real life" mean the breaker will actually trip around 1000A or at around 80% of 1000A?

If there is no relation, what would they have called out in such a drawing if they wanted to specify 100% rated? Presumably the absence of a specification means standard rated (80%).

Thanks!

 

[R Bob]

Yep.. SEDA was a GE breaker -- eventually found that by more google work.

Now when they call out Amp Trip (AT) does this have any relation to this breaker being a 80% or 100% rated? That is to say if a drawing such as this calls for "1000AT" does it "in real life" mean the breaker will actually trip around 1000A or at around 80% of 1000A?

If there is no relation, what would they have called out in such a drawing if they wanted to specify 100% rated? Presumably the absence of a specification means standard rated (80%).

Thanks!

Unless you're referring to the trip adjustment, I don't know what your asking when referring to 80% vs 100%:-?
(although I'm not a CB expert either)

If you're asking why they differentiate between AF and AT, they're using AF to designate the CB frame size and using AT to designate the rating of the plug that goes in that CB.

 

[Jraef]

Typically they would very specifically spell out a 100% trip rated breaker as it is a special order item. Assume, unless specifically directed otherwise, that all breakers are to be loaded at 80% max.

 

[iwire]

Now when they call out Amp Trip (AT) does this have any relation to this breaker being a 80% or 100% rated? That is to say if a drawing such as this calls for "1000AT" does it "in real life" mean the breaker will actually trip around 1000A or at around 80% of 1000A?

No, you can have a 1000 AF and use a 600 AT unit in it. It is much like fused disconnects, you might have a 200 amp fused disconnect switch equipped with 150 amp fuses.

Another thing, a standard '80% rated' breaker will not trip at 80%, it is rated to carry 100% up to 3 hours. If you wanted to run it at more than 80% for three hours or more than you would need a 100% rated breaker.

 

[R Bob]

No, you can have a 1000 AF and use a 600 AT unit in it. It is much like fused disconnects, you might have a 200 amp fused disconnect switch equipped with 150 amp fuses.

Another thing, a standard '80% rated' breaker will not trip at 80%, it is rated to carry 100% up to 3 hours. If you wanted to run it at more than 80% for three hours or more than you would need a 100% rated breaker.

I see what he's asking now. I thought he was asking about the specified trip settings based on a coordination study.

Based on the info the OP provided, the 1200AF, 1000AT GE SKLA CB specified has a standard/80% rating.

I think this is the CB: SKLA36AI1200
http://products.geindustrial.com/IndustrialProducts/Dispatcher?REQUEST=SPECPAGE&CATALOG=ED

 

[barclayd]

Another thing, a standard '80% rated' breaker will not trip at 80%, it is rated to carry 100% up to 3 hours. If you wanted to run it at more than 80% for three hours or more than you would need a 100% rated breaker.

Per a Square-D catalog page "Per the National Electric (sic) Code, circuit breakers may only be applied continuously at up to 80% of their rating".

I think a breaker will carry its rated current indefinitely - The limitation is based on the NEC, not the breaker.

db

 

[iwire]

Per a Square-D catalog page "Per the National Electric (sic) Code, circuit breakers may only be applied continuously at up to 80% of their rating".

I think a breaker will carry its rated current indefinitely - The limitation is based on the NEC, not the breaker.

db

I would not count on it, the 80% is from both the UL listing of standard breakers and the NEC.

You might get away with running a 80% rated breaker at 100% indefinitely but the manufacturer is going to tell you to pound sand if you go back to them complaining that it trips out at 100% after 8 hours.

 

[barclayd]

I would not count on it, the 80% is from both the UL listing of standard breakers and the NEC.

You might get away with running a 80% rated breaker at 100% indefinitely but the manufacturer is going to tell you to pound sand if you go back to them complaining that it trips out at 100% after 8 hours.

I don't know. Every trip curve I've ever seen goes asymptotic at 1 X the Rated Current.
(I love them big words like that)
Besides, I've had better people than breaker manufacturers tell me to pound sand.
db

 

[aries]

Thank you to all who replied -- it was very helpful to my understanding of the sample drawings I was looking at. And with regard to 100% rated; I did find the engineer specifically called out 100% in one or two places where it was required.

Lots to learn!