You're on the right track, but let's break this down to clarify how motor circuit protection works in accordance with the NEC and address your specific questions about elevator motor applications.

Understanding the NEC Philosophy for Motor Protection

The NEC's approach to motor circuit protection is multi-layered. It aims to:1. Protect Against Short Circuits and Ground Faults

This is the primary function of the

short-circuit and ground-fault protective device (SCGFP), typically a fuse or circuit breaker. This device must interrupt fault currents that could damage the motor or wiring.2. Protect Against Overloads

Overloads are currents above the motor's full-load current (FLA) but below short-circuit levels. These are caused by excessive mechanical load on the motor.

Overload protection is typically provided by a separate overload relay.3. Allow for Starting Inrush Current

Motors draw a significantly higher current during startup than their FLA. The SCGFP must be sized to allow this inrush current without tripping or blowing, but still provide adequate short-circuit protection.

Analyzing Your Situation Motor FLA

14.36 amps

Maximum Up Drive Acceleration Amps

86.2 amps

NEC Table 430.52 Suggests

A maximum 250% of the motor FLA for a time-delay fuse. 14.36 amps 2.5 = 35.9 amps.

Applying NEC 430.52 and Time-Delay Fuses

NEC 430.52 outlines the rules for sizing the SCGFP device. For a time-delay fuse, you're allowed up to 175% of the motor's full-load current (FLA) unless 175% is not sufficient to allow the motor to start. You can use up to 225% of the motor FLA if the 175% will not allow the motor to start. Some motors can be sized up to 400% per Table 430.52 for time delay fuses, but your motor nameplate will need to have a code letter marked on the nameplate.

Here's the breakdown for your situation


Calculate the maximum allowed fuse size

14.36 amps 1.75 = 25.13 amps or 14.36 amps 2.25 = 32.31 amps. This would lead you to use a 25 amp or 30 amp time-delay fuse.
2.

Consider the Starting Current

This is where the "time delay" characteristic of the fuse comes into play. A time-delay fuse can withstand a temporary overload (like the starting current) for a short period without blowing. However, its important to choose the correct time delay fuse to allow the equipment to start.3.

The 75A Fuse and Your Concerns

Using a 75 amp fuse directly based on the acceleration amps is NOT the correct way to use NEC 430.52. The code does not directly base the fuse size on acceleration amps. Your initial instinct is right - it would not be ideal to protect the motor in the event of a fault condition.

Addressing Your Specific Questions "Shouldn't the fuse blow unless it's over 75 amps for a while since it's a time delay fuse?" Yes, that's the general idea. A time-delay fuse requires a sustained overload to trip. This is why it allows for the brief starting inrush. However, you should not size it directly based on the acceleration amps. "Is it just super unlikely that it's going to hit 86.2 amps unless there are too many people standing in the elevator overloading it?" You're getting closer to the correct thinking here. The 86.2 amps is the maximum expected acceleration current under a specific, probably worst-case, scenario. It is a critical piece of information, but it does not dictate the fuse size directly. You need to find the correct fuse size based on the FLA of the motor as the NEC directs you.

The Importance of Overload Relays

Here's a crucial point often overlooked: The time-delay fuse is NOT intended to be the primary overload protection for the motor. Elevators, like most motor applications, must have a separate overload relay (or electronic overload protection) specifically designed to trip at sustained overcurrents that are below short-circuit levels but could damage the motor windings. This overload relay is calibrated to the motor's FLA and trips if the motor draws excessive current for too long (e.g., a prolonged overload caused by too many passengers).

How It All Works Together1. Overload Relay

Protects against sustained overloads by monitoring motor current and tripping if it exceeds a setpoint for a certain time. This prevents the motor from overheating and being damaged.2.

Time-Delay Fuse (SCGFP)

Protects against short circuits and ground faults. It's sized to allow the motor to start (and handle brief acceleration currents) but will quickly interrupt very high fault currents.

In summary

Base your initial fuse selection on the FLA of the motor per NEC 430.52, not directly on the peak acceleration current. Ensure the chosen fuse type and size are appropriate for the starting characteristics of the elevator motor. A time-delay fuse is necessary.* The overload relay provides the primary protection against overloads, while the fuse protects against short circuits and ground faults.

Recommendation:

Consult with a qualified electrical engineer experienced in elevator installations to ensure your motor circuit protection is compliant with the NEC and provides adequate protection for your specific application. They will also be able to advise on appropriate time delay fuse curves for your application. Flag for review