Minimum Overcurrent Protection (OCP) on Service

[jaggedben]

I agree but It is unlikely the overcurrent protective device will be sized less than the conductors especially based on 230.79 where the largest would be 100 amp. I also bet that most authority having jurisdiction's will read this section and require 100 amp overcurrent protective device for a dwelling service. If the disconnect and conductors must be 100 amp why would you install a smaller overcurrent protective device.

I have tried to write a change for this section but they insist it is the way they want it.... I don't think they understand what they had written because it makes no sense.

I think the OP has posed a great question that epitomizes the real issue, and it really has nothing to do with the minimums in 230.79. That is just the best answer to the question we've been able to come up with.

The OP has a 450A calculated load and an existing 400A OCPD. Presumably he would rather not pay to replace a not-super-cheap breaker if there isn't a good reason to. And thus the question is: where does the code provide a clear, explicit obligation to replace the 400A breaker? If he does his remodel and the 400A breaker doesn't trip in a week, or a month, or a year, or ten years.... Is he obligated to upsize the OCPD?

 

[lmcgill]

I think the OP has posed a great question that epitomizes the real issue, and it really has nothing to do with the minimums in 230.79. That is just the best answer to the question we've been able to come up with.

The OP has a 450A calculated load and an existing 400A OCPD. Presumably he would rather not pay to replace a not-super-cheap breaker if there isn't a good reason to. And thus the question is: where does the code provide a clear, explicit obligation to replace the 400A breaker? If he does his remodel and the 400A breaker doesn't trip in a week, or a month, or a year, or ten years.... Is he obligated to upsize the OCPD?

Yes, you hit the nail on the head here. As most of you correctly inferred, the 400A circuit breaker is, indeed, the building's service disconnect. So, although the code doesn't explicitly dictate a minimum OCP rating for services, 230.79 does bite me in the rear by dictating a minimum service disconnect size. I try to do a lot of research before I actually ask the question (in fact this may be my first post), and you all did a wonderful job pointing to me to the right answer. Thank you!