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Feeder sizing playbook

Goal​

Size a feeder based on calculated demand, conductor ampacity, and OCPD requirements with a clear inspection trail.

Inputs you must know before you start​

  • Calculated demand load and diversity assumptions.
  • Installation method, ambient conditions, and conductor counts.
  • Available standard OCPD ratings and equipment terminations.
  • Grounding and bonding method for the system.

The path (in order)​

  1. Calculate demand load for the feeder.
  2. Select conductors based on ampacity and adjustment factors.
  3. Choose OCPD from standard ratings that match the conductor limits.
  4. Confirm grounding and bonding conductors are sized and connected.
  5. Verify raceway fill and installation constraints.
  6. Document assumptions, references, and final selections.

This is​

A repeatable method for sizing feeders using demand calculations and standard ampacity/OCPD logic.

This is not​

A substitute for engineering studies or specialty system design.

Inspection-ready checklist​

  • Demand calculation documented with references.
  • Conductor ampacity after adjustment recorded.
  • OCPD rating consistent with conductor limits.
  • Grounding and bonding conductors verified.
  • Raceway fill and routing checked.

Worked example​

A feeder serving multiple loads is sized from a demand calculation, then conductors are selected with ambient corrections. The OCPD is chosen from a standard rating that does not exceed conductor limits, and the raceway fill is checked before installation.

Cross references​

  • Primary: 215, 220
  • Secondary: 310, 240, 110.14(C), 250

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