80% rated breakers

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Cableman

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I am reviewing drawings on behalf of a municipality. The consultant designed a system with a 80%,rated breaker, 1600A frame, 1200A trip (1200AT/1600AF). The main breaker can see 1100A of continuous load, and the consultant said he can do this. Please let me know if it is allowable by code to load this breaker setup to 1100A? Please state where in the code you derive your answer.

Thanks for your time.
 
I am not sure why you are questioning this. If a breaker is rated 80% for continuous load then the math , as you showed, should be sufficient. I see no issue with loading to 1100 amps on a 1600 amp breaker.
 
Dennis Alwon said:
I am not sure why you are questioning this. If a breaker is rated 80% for continuous load then the math , as you showed, should be sufficient. I see no issue with loading to 1100 amps on a 1600 amp breaker.
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It is a 1600 amp frame size with a 1200 amp trip unit. If you have 1100 amps of continuous load the 1200 amp trip unit is too small.

However I think it is unlikely that the entire 1100 amps is a continuous load and if the 1100 amps was arrived at using Article 220 the continuous and non-continuous load have already been accounted for. If this is the case an 1100 amp trip unit would be OK.
 
Dennis Alwon said:
I am not sure why you are questioning this. If a breaker is rated 80% for continuous load then the math , as you showed, should be sufficient. I see no issue with loading to 1100 amps on a 1600 amp breaker.
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I thinks he is questioning if 1100 amps is allowed because 80% of the 1200 amp trip point would only be 960 amps.

Is the 80% rating based on the 1600 amp frame size or on the trip setting?
 
As Bob said if the 1100 amps is truly all continuous then you would need a minimum trip setting of 1375 amps (1100 * 125%) and the conductors to match.

kwired said:
Is the 80% rating based on the 1600 amp frame size or on the trip setting?
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Frame size is really irrelevant here.
 
infinity said:
Frame size is really irrelevant here.
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I agree also and it should be forgotten as far as this conversation goes, we are discussing a 1200 amp breaker (trip unit) regardless of what is housing it.

Roger
 
iwire said:
It is a 1600 amp frame size with a 1200 amp trip unit. .
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You see I shouldn't be answering these question as I know nothing about these breakers. I thought the op was saying it is a 1600 amp breaker rated 1200 amps at 80%. I now see that 80% is 1280 not 1200 and realize my mistake.
 
infinity said:
As Bob said if the 1100 amps is truly all continuous then you would need a minimum trip setting of 1375 amps (1100 * 125%) and the conductors to match.



Frame size is really irrelevant here.
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That was my thought but I hardly ever run into breakers that have adjustable settings other then a magnetic/instantaneous trip setting.

I always thought if adjustable than if set at 1200 amps you treat it like it were 1200 amp non adjustable with allowable load as well as conductor size.
 
Dennis Alwon said:
You see I shouldn't be answering these question as I know nothing about these breakers. I thought the op was saying it is a 1600 amp breaker rated 1200 amps at 80%. I now see that 80% is 1280 not 1200 and realize my mistake.
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Totally understandable assumption. :)

I don't know that much about them, I just know that for various frame type and sizes engineers can choose different types of trip units from non-adjustable types, to thermal magnetic adjustable types to fully electronic types that have many available settings to change.

I will try to find a picture.
 
I do not know what frame size this is but is equipped with an electronic trip unit and 2500 amp rating plug.

06dd3879.jpg
 
Thanks Bob. That, of course, is way out of my league. :grin: I bet that breaker cost as much, if not more than, most jobs that I do.:)
 
infinity said:
As Bob said if the 1100 amps is truly all continuous then you would need a minimum trip setting of 1375 amps (1100 * 125%) and the conductors to match.



Frame size is really irrelevant here.
Click to expand...

I want to thank everyone for responding and helping out. This is a great forum
 
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