# Complex Imaginary vol.1 #69.



## BebeshKing PE (Dec 3, 2020)

Should the answer for this problem be letter C?

First thing is, 180A is not a standard size breaker. Second is, per NEC Art.240.4(B)(2), if the ampacity of the conductor does not correspond with the standard ampere rating of a fuse or breaker, we can use the next higher standard size.

Does anyone agree?


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## Byk (Dec 4, 2020)

According to the NEC the 180A breaker does not existing. 

I would chose C, 200A for my answer.


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## DilutedAr18_PE (Dec 4, 2020)

@Byk is correct. 175A would be the next smaller standard size according to 240.6. 175A is allowable, but the maximum would be 200A.


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## akyip (Dec 4, 2020)

In all fairness, the question doesn't ask for a maximum standard size, only an allowed maximum.

It's rare, but I have seen a few questions that have asked only for a maximum or minimum, not necessarily a standard size.

One example I remember is from Zach Stone's Electrical PE Review exam. He has a question about the minimum disconnect rating for a circuit feeding multiple hoists or something similar. In his solution for this problem, he states that he is only looking for the minimum rating, not necessarily the standard size since the problem did not ask for standard size.

Just putting my 2 cents in...


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## Byk (Dec 4, 2020)

akyip said:


> In all fairness, the question doesn't ask for a maximum standard size, only an allowed maximum.
> 
> It's rare, but I have seen a few questions that have asked only for a maximum or minimum, not necessarily a standard size.
> 
> ...


I mean the answer states "Breaker Chosen". I don't see how can you chose something that does not exist.


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## akyip (Dec 4, 2020)

Byk said:


> I mean the answer states "Breaker Chosen". I don't see how can you chose something that does not exist.


You're talking about NEC Table 240.6(A), right?

My interpretation/understanding is this: Table 240.6(A) is for STANDARD sizes. There can also exist circuit breakers and fuses with non-standard sizes. These days I believe there are electronic-style breakers, fuses, and OCPDS whose trip setting can be set to whatever amount is needed. So those would not have to necessarily correspond with a standard size...

And again, this question didn't ask for a standard size. It's rare, but again I have seen a few questions that only ask for a maximum or minimum, not necessarily a standard.


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## Byk (Dec 4, 2020)

akyip said:


> You're talking about NEC Table 240.6(A), right?
> 
> My interpretation/understanding is this: Table 240.6(A) is for STANDARD sizes. There can also exist circuit breakers and fuses with non-standard sizes. These days I believe there are electronic-style breakers, fuses, and OCPDS whose trip setting can be set to whatever amount is needed. So those would not have to necessarily correspond with a standard size...
> 
> And again, this question didn't ask for a standard size. It's rare, but again I have seen a few questions that only ask for a maximum or minimum, not necessarily a standard.


I am yet to see a breaker that is rated at 180A. (Maybe one day).

However, I read the problem again and now I am curios to see if the problem says feeding 277V load or loads. If it's loads then you cannot round it up (we wouldn't meet 240.4(B) requirements)

Practically speaking you want your breaker to have smaller rating then your wire.  You want your breaker to trip before your wires burn down. 

However, I am still not convinced that 180A is correct answer.


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## DilutedAr18_PE (Dec 4, 2020)

Byk said:


> I am yet to see a breaker that is rated at 180A. (Maybe one day).
> 
> However, I read the problem again and now I am curios to see if the problem says feeding 277V load or loads. If it's loads then you cannot round it up (we wouldn't meet 240.4(B) requirements)
> 
> ...


It says “a”, so it would be incorrect grammar to be “loads”. I think it’s just a question mark. 



akyip said:


> You're talking about NEC Table 240.6(A), right?
> 
> My interpretation/understanding is this: Table 240.6(A) is for STANDARD sizes. There can also exist circuit breakers and fuses with non-standard sizes. These days I believe there are electronic-style breakers, fuses, and OCPDS whose trip setting can be set to whatever amount is needed. So those would not have to necessarily correspond with a standard size...
> 
> And again, this question didn't ask for a standard size. It's rare, but again I have seen a few questions that only ask for a maximum or minimum, not necessarily a standard.


The electronic trip units are used to adjust the time setting for selective coordination. Your LSI settings of electronic trip breakers allow you to adjust your Long-time pickup, Long-time delay, Short-time pickup, Short-time delay, Instantaneous pickup. If you add ground fault protection on it would be an LSIG electronic trip circuit breaker. The rating of the ampacity is still set at standard overcurrent device sizes. 

There are a few “funny” sizes for standard overcurrent protective devices if you read the paragraph preceding the table in 240.6. “Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601”. The 601A is in there specifically for a 600A fuse that fits into a different class of fuse holder. They needed to distinguish between the two, so they rate the one with a 1A additional rating and made it a standard rating.


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## Ampera18 PE (Dec 5, 2020)

Byk said:


> I am yet to see a breaker that is rated at 180A. (Maybe one day).
> 
> However, I read the problem again and now I am curios to see if the problem says feeding 277V load or loads. If it's loads then you cannot round it up (we wouldn't meet 240.4(B) requirements)
> 
> ...


You can get a 200A adjustable breaker. I have seen 3200AF/AT breakers (not a standard size).

The NEC lets you get away with the next standard size up to 800A rating.


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