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Transformer secondary tap playbook

Goal​

Confirm transformer secondary conductors meet tap length and protection rules.

Inputs you must know before you start​

  • Transformer ratings and primary/secondary OCPD.
  • Secondary conductor length and routing.
  • Termination temperature ratings and conductor type.

The path (in order)​

  1. Identify the applicable transformer secondary conductor rule.
  2. Measure the secondary conductor length and routing.
  3. Verify conductor ampacity and termination ratings.
  4. Confirm OCPD aligns with transformer protection rules.
  5. Label and document the secondary tap conditions.

This is​

A checklist focused on transformer secondary conductor compliance.

This is not​

A transformer sizing or grounding/bonding guide.

Inspection-ready checklist​

  • Applicable transformer tap rule identified.
  • Secondary conductor length within limits.
  • Conductor ampacity and terminations verified.
  • OCPD alignment with transformer protection rules.
  • Documentation updated for inspection.

Worked example​

A transformer feeds a nearby panel with a short secondary run. You confirm the secondary length meets the rule, size conductors per termination ratings, and verify the primary OCPD aligns with transformer protection requirements.

Cross references​

  • Primary: 240.21(C)
  • Secondary: 450.3, 310.16

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