110.24 Available Fault Current.
Code Change Summary: A new informational note was added.
Since the 2011 edition of the NEC®, section 110.24 has required the maximum available fault current, and fault current calculation date, to be legibly field marked on service equipment in other than dwelling units. This marking requirement has created both awareness and confusion in the field.
The intent of this section is to ensure that equipment short circuit current ratings (SCCR’s) are considered and equipment is properly selected based on the available fault current in order to comply with 110.9 and 110.10. These two code sections have been in the NEC® for many years.
Since section 110.24 arrived in 2011, many people have been incorrectly using the numeric available fault current values for other purposes such as determining potential arc-flash exposure, or selecting levels of personal protective equipment (PPE) based on the task categories found in NFPA 70E Standard for Electrical Safety in the Workplace.
Determining incident energy or selecting PPE was never the intent of section 110.24. Now, a new informational note lets the user know that this section is only for equipment selection and that NFPA 70E should be used to determine proper levels of PPE.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2011 Code Language:
110.24 Available Fault Current.
(A) Field Marking. Service equipment in 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.
2014 Code Language:
110.24 Available Fault Current.
(A) Field Marking. Service equipment in 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.
Informational Note: The available fault-current marking(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.