Tap conductor sizing wrapper
Why you care (60 seconds)
Tap conductor sizing is often what inspectors check first. If the conductors are undersized or protected incorrectly, the tap fails.
Where people lose time
- Sizing taps as if they were full feeders.
- Ignoring termination temperature ratings.
- Forgetting ampacity adjustments for conditions of use.
This is
The rule in plain language
Tap conductors must meet ampacity and protection conditions defined by the tap rule being used, including termination limitations.
When it applies
Any time a conductor is tapped ahead of its overcurrent device.
What you must do (checklist)
- Choose the tap rule and verify its ampacity conditions.
- Size conductors for the tap length and load.
- Apply termination temperature limits to ampacity.
- Document the tap rule and conductor size.
Quick examples
- A short tap still needs ampacity sized to its allowed rule.
- Termination ratings can reduce usable ampacity.
This is not
Common misreads
- Assuming tap conductors can be smaller without limits.
- Using feeder or branch circuit sizing rules without the tap rule.
What it doesn't cover
- Voltage drop recommendations.
- Transformer primary protection.
False friends
- "Same size as feeder" is not always required, but it must meet the rule.
Exceptions & edge cases
- Tap rules vary based on length and location.
- Parallel conductors have additional sizing requirements.
Cross-references (NEC map)
- Primary: 240.21
- Secondary: 240.4, 310.16
Exam traps
- Missing termination rating adjustments.
- Confusing tap sizing with standard feeder sizing.
Field notes
- Verify termination temperature ratings before final sizing.
- Keep tap sizing notes with the one-line drawing.
AHJ / Local amendments notes (placeholder)
- Add local amendments or interpretations here.
Revision notes
- Draft wrapper created for tap conductor sizing.