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NEC Art.430
Validated against the standard.
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How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NEC Art.430 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
HVAC equipment has its own electrical rules. The nameplate gives a minimum circuit ampacity (MCA) and a maximum overcurrent protection (MOCP), and you size the conductors and breaker to those — not by the running amps. This app applies the NEC Article 440 and 430 rules so the disconnect, wire, and breaker all match the unit.
How it works
- MCA sets the minimum conductor ampacity — size the wire to carry at least the MCA.
- MOCP sets the maximum breaker or fuse — never go above it, and usually do not round up past it.
- For field-built circuits the app applies 125% of the largest motor plus the sum of the others, per Article 430.
Worked example
A condensing unit with MCA = 24.6 A and MOCP = 40 A: size the conductors for at least 24.6 A (so #10 copper), and protect with a breaker no larger than 40 A, exactly as the data plate states.
Related calculators
For general circuits see the electrical suite; size duct and airflow with the duct sizing calculator and airflow CFM calculator.
HVAC electrical FAQ
Why use MCA and MOCP instead of running amps?
Air-conditioning and refrigeration equipment is covered by NEC Article 440, which requires sizing conductors to the nameplate minimum circuit ampacity and limiting protection to the maximum overcurrent protective device printed on the unit.
Can I round the breaker up to the next size?
Not past the MOCP. The maximum overcurrent protection is a hard ceiling; you choose a standard size at or below it.
Does it size the conductors too?
Yes. It selects a conductor with ampacity at least equal to the MCA, accounting for the temperature column and any derating you enter.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
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