You're right to be cautious and double-check! Here's the breakdown of what you need to do, and why

Understanding the Discrepancy

The fact that your calculated amperage based on motor horsepower is significantly lower than the nameplate FLA (Full Load Amps) indicates the crane's nameplate already includes all necessary adjustments for intermittent duty, starting currents, and other factors specific to crane operation. Never override nameplate data with a calculated value for equipment that has a nameplate.NEC Requirements for Crane Branch Circuits

Article 610 of the NEC (National Electrical Code) covers cranes and hoists. Here's the relevant section based on your scenario: 610.14(A): Ampacity. The conductors supplying the crane must have an ampacity not less than the larger of:1. 125 percent of the motor with the highest rated horsepower, plus the full-load currents of all other motors and other equipment.2. The crane nameplate rating.

Your Situation1. Nameplate Rating

Your crane's nameplate states a required circuit ampacity of 115 amps.2.

Calculation

Your individual calculation, presumably based on the largest motor, resulted in a lower value.

Conclusion

According to NEC 610.14(A), you must use the crane's nameplate rating of 115 amps. This is because the nameplate is considered to reflect the overall demands of the equipment more accurately than a simple horsepower calculation.

Wire Sizing You need wire with an ampacity of at least 115 amps. Using the 75°C column of NEC Table 310.16, a #2 AWG THHN conductor is sufficient (it's rated for 115 amps).

Overcurrent Protection (Circuit Breaker or Fuses) NEC 610.16 governs overcurrent protection. Typically, you can protect a circuit at a value that exceeds the wire ampacity. The NEC allows for flexibility in sizing the overcurrent device (OCPD) to accommodate motor starting currents. A common approach is to start with 150% of the nameplate ampacity and potentially go higher if needed to prevent nuisance tripping during starts. Consult NEC 610.16 and 430 (Motors, Motor Circuits, and Controllers) for the specific rules and maximum allowable values.Important Considerations Ambient Temperature Correction

If your conductors are installed in an area with a high ambient temperature (higher than 30°C or 86°F), you may need to apply a temperature correction factor to the wire ampacity. Check NEC Table 310.16 note.

Conduit Fill

Ensure that your conduit fill (the percentage of the conduit's cross-sectional area occupied by conductors) does not exceed the limits specified in the NEC.

Voltage Drop

While your wire size is adequate for the ampacity, also calculate the voltage drop to ensure it's within acceptable limits, especially for longer runs. Excessive voltage drop can harm the crane's performance and lifespan.

Local Codes

Always check with your local electrical inspector and adhere to any local amendments to the NEC.

Qualified Electrician

This advice is for informational purposes only. All electrical work should be performed by a qualified and licensed electrician to ensure safety and compliance with all applicable codes.

In summary: Use the nameplate ampacity of 115 amps, which will require #2 AWG THHN conductors. Then, correctly size your overcurrent protection according to NEC Article 610 and 430. Have a qualified electrician perform the work! Flag for review