This week’s question is about the 2014 National Electrical Code. In particular, the following section:

110.24 Available Fault Current (A) Field Marking. Service equipment in other than dwelling units shall be legibly marked in the filed with the maximum available fault current The field marking(s) shall include the date the fault current calculations was performed and be of sufficiently durability to withstand the environment involved.

A new informational note was added for the 2014 NEC to emphasize that this information is NOT for arc flash studies. Apparently some thought this was related to arc flash studies - perfectly understandable.

(NEW) Informational Note: The available fault current making (s) addressed in 110.24 is related to required short circuit current ratings of equipment. NFPA 70E-2012 Standard for Electrical Safety in the Workplace, provides assistance in determining the severity of potential exposure, planning safe work practices, and selecting personal protective equipment.

Did you consider when 110.24 was introduced in 2011, that it WAS related to arc flash studies? (Perhaps for the footnotes in the Hazard Risk Tables)

• Yes - it seemed related
• No
• Never thought about it

This requirement was previously required on industrial control panels only. I saw the arc flash requirement but it really does not provide enough information since most practitioners tend ^o give very conservative estimates for AIC purposes which is just the opposite result for arc flash purposes where overestimating short circuit current results in faster trip times. I have seen many cases of breakers that are set correctly when considering only say transformer impedance and inrush but unacceptable arcing fault trip times and sometimes with long cable lengths, would not even adequately trip for bolted fault conditions.

What is needed on industrial control panels is the SCCR (short-circuit current rating) that the panel and it's components can withstand safely (normally comes from the method described in UL 508A Supplement SB). There are some other types of equipment which have a similar requirement as well.
What 110.24 asks is the available fault current at a given point in a distribution system, so the sparky installing a new ICP can easily verify if the panel's SCCR is high enough for the available fault current. If it's not posted, the sparky needs to check transformers, feeders and branch leading to the installation point. It closes the loop on the SCCR requirement.

I considered it for two reasons. One was the 2011 NEC Handbook discusses it in the highlighted explanation notes and we have the available fault current printed on our AFH labels

I thought it might have been introduced in 2011 to keep the HRC tables "alive" Since more people perform calculations and the HRC tables require knowing the short circuit current, it seemed logical. It is interesting that NFPA had to add a not to state that it is not used for arc flash. Will this start a trend where NFPA has to describe what all the other articles "are not used for"? Interesting.