1200 A main Service Breaker

[egr]

I am new to this forum, I have looked at the previous posts, but could not find the answer to the following questions:

In regards to NEC 230.95 Requirements, is a service protected by a 1200 A (MCCB) breaker required to have GFP? Part of my confusion arises from the fact that I believe that this breaker could not have a trip plug of more than 960 A...assuming a regular as opposed to a 100% rated breaker

Along the same lines if I am deriving a service from a 750 KVA utility-owned trasformer, and my intend is to size this conductors to deliver the FLC of the transformer, ~ 902 A. Would this set of conductors considered to be a 1000 A or more service in regards to 230.95...? i.e. 902 * 1.25 = 1128 A

I should mention that questions 1 and 2 are two separate instances...

Best regards

 

[charlie b]

My answer to both questions is the same: It is the rating of the disconnect that matters, not the selection of conductor sizes or the setpoint of the overcurrent trip. In the first instance, the "service disconnecting means" is a breaker that is rated at 1200 amps (no matter what setpoint you use for the overcurrent trip). In the second instance, you need to use a disconnecting means whose rating exceeds 800 amps (because you need 902 amps as a minimum), and the next standard size is 1000 amps. So you need GFP protection in both cases.

 

[augie47]

setting

setting

charlie, if the conditions of 240.6(c) were met, could you not size by the "set-point" ?

egr, what is the system voltage ?

 

[chris kennedy]

what is the system voltage ?

Key Question.

"services of more than 150 volts to to ground"

 

[egr]

The system voltage in both instances is 480/277 V.

Thanks for the input

EGR:smile:

 

[charlie b]

charlie, if the conditions of 240.6(c) were met, could you not size by the "set-point" ?

That is a new one on me. Thanks for pointing it out. I believe you could use the setpoint as the rating of a breaker in that manner, and thereby avoid having to install the GFP.

 

[don_resqcapt19]

Part of my confusion arises from the fact that I believe that this breaker could not have a trip plug of more than 960 A

There is no reason that a 1200 amp breaker has to have a trip plug with a rating of less than 1200 amps. The 80% limit is an artifical limit to prevent excessive heat build-up from tripping the breaker. When UL tests the breaker it will be tested in the open at 100% of the rating.
Don

 

[Jomaul]

If I am not mistaken 230.95 states that the rating of the service disconnect shall be the rating of the largest fuse that can be installed or the highest continous current trip setting the breaker can be adjusted to so wouldn't the 1200 amp rating be the highest rating and the fact that you can adjust the trip rating lower would not matter. and GFCI protection would be required.

 

[charlie b]

Jomaul: Take a look at the code article cited by Augie47 in the third post of this thread, and tell me what you think.

 

[Jomaul]

I have read the code article however the original question asked does not state that the conditions of article 240.6 c were met and your 1st post would be the correct answer. Now if we gained more information that the conditions of 240.6 were met then thats another story.

 

[charlie b]

. . . the original question asked does not state that the conditions of article 240.6 c were met and your 1st post would be the correct answer.

Quite true. But you'll observe that Augie47's post included the word "if." He was asking whether, "if" those conditions were met, I would change my answer. I agreed with him, and I gather you would too, "if" the conditions were met.

 

[Jomaul]

I missed the word if.Thats whats great about this form. it helps keep you sharp. thanks

 

[egr]

Well, eventhough I posted the original question, the truth is I do not have all the information myself....
Here is what I know: The breaker would be contained in an out door enclosure, it is unlikely that 240.6 (c) conditions would be met...

EGR