More documentation is being required in the National Electrical Code and NFPA 70E, the Standard for Electrical Safety in the Workplace. The words “documented” or “documentation” appear in the 2017 NEC approximately 104 times, 100 times in the 2020 NEC and about 37 times in NFPA 70E. The problem with these two words is how they are used in each instance and how important this use is.
I first started to question the use of these two words a few years ago, and the more I saw “documented” and “documentation” used while trying to access the documentation, the more I questioned the expanded use in code and standards. What does “documentation” or “documented” mean where is it used in the NEC and the NFPA 70E, and when should documentation be made available? These questions may prompt the NEC Correlating Committee, the NEC panels and the NFPA 70E Committee to better address this issue.
The first location in the NEC using the word “documented” is in 110.24(A) and its informational note, covering available fault current for service equipment.
It states: “(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: The available fault-current marking(s) addressed in 110.24 is related to required short-circuit current ratings of equipment. NFPA 70E-2015, 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.”
I want to run through an example to explain the part of the text about documentation, which is reasonably consistent throughout any of the locations where these words are used in the NEC and NFPA 70E. In 110.24, the purpose of field-marking the service equipment, other than for dwelling units, with the maximum available fault current is to provide the maximum actual fault current that is delivered to the electrical service by the utility company. Most electrical utility companies provide the maximum available fault on the secondary side of their transformers based on what they call the infinite bus on the primary side of their transformer, using the impedance of the transformer primary to secondary windings.
This fault-current value at the utility company transformer secondary can then be used to calculate the available fault current at the electrical service for the facility by using the phase conductors’ impedance from the secondary to the service equipment.
Electrical engineers and electrical contractors then use this fault-current calculation to design the electrical service with bracing of the busing and electrical service equipment. The electrical service equipment will have this fault current bracing indicated on the equipment’s label.
Since infinite busing is used to calculate the utility company fault current, the bracing of the electrical service equipment is usually much greater than the actual fault current value being delivered to the service.
For example, let’s say that the infinite bus fault current value was 65,000 amperes (A), the actual bolted fault current may be closer to 45,000A. The value of 45,000A, not 65,000A, should be used to determine the length of time necessary to open the service overcurrent device. This calculated value of 45,000A, with the date the calculation was performed, can then be marked in the field on a label at the service.
This available fault-current value can then be used for assistance in determining the severity of potential exposure to an arcing event, planning safe work practices and selecting personal protective equipment based on NFPA 70E.
Remember, “The calculation shall be documented and made available to those authorized to design, install, inspect, maintain, or operate the system.”
This sentence requires documentation be made available to authorized people who design, install, inspect, maintain and operate the equipment. The label is on the equipment with the fault current availability, but where is the documentation that details the calculations?
Sometimes I believe there is a deep dark hole in offices where this calculation documentation is put, never to see the light again, especially when the property changes ownership or management. The NEC and NFPA 70E need to be changed to require this calculation documentation to be installed in a print pocket inside the door of the electrical equipment where it is readily available to all authorized personnel.