1-183 Log #4783 NEC-P01Final Action: Accept in Principle
_______________________________________________________________TCC Action: The Technical Correlating Committee directs that the Chairs
of Code-Making Panels 1 and 10 form a Task Group to correlate the
actions taken on Proposals 10-72 and 1-183.
Submitter:Michael J. Johnston, National Electrical Contractors Association
Recommendation: Add the following new text:
I commented that that should be deleted before it is put into the NEC.
110.24 Available Fault Current
(A) Field Marking.Service equipment in other than dwelling units shall be
legibly marked in the field with the available fault current. The field marking(s)
shall include the installation date and be of sufficient durability to withstand
the environment involved.
(B) Modifications.When modifications to the electrical installation occur, that
affect the available fault current at the service, the available fault current shall
be verified or recalculated as necessary to ensure the service equipment
interrupting ratings are sufficient for the available fault current at the line
terminals of the equipment. The required field marking(s) in (A) above shall be
adjusted to reflect the new level of available fault current.
Exception: The field marking requirements in (A) and (B) shall not be
required in industrial installations where conditions of maintenance and
supervision ensure that only qualified persons service the equipment.Panel Statement:The revised recommendation meets the intent of the
If available fault current is marked on equipment, it will almost always be established conservatively, so that the value is artificially high. Often it will be calculated using an infinite primary transformer calculation. This is satisfactory for interrupting capacity and withstand comparisons for equipment selection, but could result in death to an electrical worker that uses this information to determine incident energy values. When marked fault current is artificially high, it will often result in theoretically faster acting inverse time overcurrent protective device; lower incident energy and eventually a lower PPE requirement will result. An electrical worker performing testing or other energized work may be hurt or killed from inadequate PPE selection stemming from the use of artificially high fault current values.