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Fault Current Studies:

The fault current calculation is the most basic calculation performed on a power distribution system and vital for the proper electrical equipment application. There are several NEC sections with requirements directly pertaining to the proper electrical product application and available fault current. Safe and reliable electrical equipment application, including OCPDs, relies on such power systems analysis study information obtained from fault current and selective coordination studies.

Knowing available fault current throughout the power distribution system is important for proper product application. The NEC recognizes the importance of fault currents in many areas within its requirements, including these important topics and sections:

Available Fault Current Markings

  • 24 — Service Entrance Equipment
  • 22(B) — Industrial Control Panels
  • 10(B) — Air Conditioning & Refrigeration Equipment
  • 51(D)(2) — Elevator Control Panels
  • 5(2) — Industrial Machinery

Applying Solutions Within Their Ratings

  • 9 — Interrupting Rating
  • 10 — Component Protection
  • 24 — Available Fault Current
  • 4 — Conductor Protection
  • 122 — Equipment Grounding Conductor Protection
  • 22(A) — Industrial Control Panels
  • 10(A) — Air Conditioning & Refrigeration Equipment
  • 16(B) — Elevator Control Panels
  • 5(1) — Industrial Machinery

Marking Short-Circuit Current Ratings (SCCR)

  • 82(3) — Meter Disconnect
  • 110(4) — Industrial Control Panels
  • 8 — Motor Controllers
  • 98 — Motor Control Centers
  • 4(B) — Air Conditioning & Refrigeration Equipment
  • 16(A) — Elevator Control Panel
  • 3(A)(4) — Industrial Machinery
  • 5(E) — Transfer Equipment for Emergency Systems
  • 5(D) — Transfer Equipment for Legally Required and Standby Systems
  • 5 — Transfer Equipment for Optional Standby Systems
  • 24(E) — Transfer Equipment for Critical Operations Power Systems