110.24 Potential Change

[yesterlectric]

Looking for comments on why this proposal may or may not be a good idea. 110.24 deals with equipment compatibility and 110.16 deals with arc flash protection. Thus, in my view someone installing a smaller system having little to no motor load (or other fault current contributing load) should have the option to utilize infinite bus calculations for this labeling, and not be required to consider impedance of conductors on line and load side of the utility xfmr as part of deriving the value for this labeling. Yet the language would currently require the calculated available fault current be posted, something which complicates the calculation and requires more information that the utility company may change during line upgrades. The intent of the change is to require only that maximum values be posted.



110.24 Available Fault Current.
(A) Field Marking.
Service equipment at other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault-current calculation was performed and be of sufficient durability to withstand the environment involved. The calculation shall be documented and made available to those authorized to design, install, inspect, maintain, or operate the system.

Informational Note No. 2: Values of available fault current for use in determining appropriate minimum short-circuit current and interrupting ratings of service equipment are available from electric utilities in published or other forms.

 

[letgomywago]

I honestly want to know how big of a kaboom to expect. 50 ft of conductor makes a crazy big difference on fault current. The bucket on the pole by my house would've been to big to feed an old school 10kaic main panel but the overhead conductor brings it down big time so it's much more limited.

 

[don_resqcapt19]

That was a change made in the 2020 code. There were various terms used for fault current in the code and those terms were replaced with the term "available fault current". The definition of that term in Article 100 tells you that this is the "largest amount of current" that could be delivered into a short circuit at that point on the circuit.