You've hit on some key points regarding motor circuits and how they are protected. Let's break this down

Understanding Motor Inrush and Overcurrent Protection
Motor Inrush (Starting Current)

Motors draw a significantly higher current during startup (inrush) than their running current. This inrush can be 6-8 times the full load current (FLA) or even higher.

NEC Article 430 (Motors, Motor Circuits, and Controllers)

The NEC allows for higher overcurrent protection (OCPD) for motor branch circuits precisely to handle this inrush. It's

not primarily about protecting the motor conductors during normal operation. It's about letting the motor start without nuisance tripping. Branch Circuit OCPD (Your 90A Fuses)

The 175% (or higher if necessary) rule for the motor branch circuit OCPD (your 90A fuses) is calculated based on the motor's FLA. This is to allow for the inrush current without tripping. The actual conductor size is based on 125% of the motor FLA (to handle continuous operation, not inrush).

Upstream Overcurrent Protection (Your 60A Breaker)

This is where it gets tricky, and your questions are valid. The upstream breaker

does need to withstand the motor inrush.

Why Your Upstream Breaker Likely Won't Trip


Breaker Time-Current Curves

Circuit breakers don't trip instantaneously at their rated current. They have time-current curves. This means they can handle short-duration overloads above their rating without tripping. The breaker is chosen to have a curve that allows for the inrush current duration without tripping while still protecting the circuit from sustained overloads.2.

Load Diversity

If this is a panel serving multiple loads, including the motor, the upstream breaker needs to handle the total load. It's possible the motor is only a portion of the total load, and the 60A breaker is sufficient for the other loads plus a brief motor inrush.3.

Motor Starting Method

The type of motor starting method (e.g., across-the-line, reduced voltage starter) significantly impacts the inrush current. Reduced voltage starters lower the inrush, making it easier for an upstream breaker to handle.

Why Not Size the Upstream Breaker the Same as the Motor Branch Circuit OCPD? Coordination

You don't want the upstream breaker to trip before the branch circuit fuse in the event of a fault in the motor branch circuit. If the upstream breaker is sized higher than the branch circuit OCPD, it may not trip quickly enough to protect the motor and branch circuit components in a fault scenario.

Protection of Other Loads

The upstream breaker protects the entire panel and other loads connected to it, not just the motor. It needs to be sized appropriately for all loads.

Conductor Protection

The upstream breaker protects the panel's main conductors leading up to the motor branch circuit. These conductors may be smaller than the motor branch circuit conductors, hence requiring lower protection.

Protecting Your 65A Rated Conductors

This is the MOST IMPORTANT part of your question and a valid concern. Here's the deal:

NEC 240.4(B) and (D)

Typically, you protect conductors at their ampacity rating (65A in your case). However, there are exceptions:

NEC 240.4(B) "Next Higher Standard Overcurrent Device Rating"

After applying any adjustment or correction factors, if the calculated conductor ampacity does not correspond to a standard OCPD size per 240.6(A), you are permitted to go up to the next higher standard size of OCPD as long as you meet all of the following:1. The conductors are not part of a multi-outlet branch circuit supplying receptacles for cord-and-plug equipment.
2. The ampacity of the conductors, after the application of any adjustment or correction factors, corresponds to a standard ampere rating OCPD3. The next higher standard device rating does not exceed 800 amperes.This may allow you to use a 70A breaker to protect the 65A conductors if you can meet all three requirements listed above.

NEC 430.52(C)(1) Motor Branch-Circuit Short-Circuit and Ground-Fault Protection

The main exception is for motor branch circuits, as you've noted. Article 430 allows for much higher OCPD than the conductor ampacity for motor branch circuits. HOWEVER, this applies

only to the motor branch circuit conductors between the motor starter (or controller) and the motor. Your Control Panel

Your conductors rated for 65A seem to be upstream of the motor branch circuit OCPD (the 90A fuses). If this is the case, and they are supplying multiple loads, you

absolutely must protect them at or below their 65A ampacity.

In Summary, Here's What You Need To Do


Confirm Panel Load Calculation

Ensure that your 60A upstream breaker is properly sized for the total load on the panel, including the motor. If the calculated load is greater than the breaker capacity, you'll need a larger breaker.2.

Verify Conductor Protection

If the 65A conductors are feeding multiple loads, including the motor, you

must protect them at or below 65A. You can do this with a properly sized circuit breaker or fuses located upstream of those conductors, inside the control panel. If the 65A conductors are only supplying the motor branch circuit after the 90A fuses, this is likely acceptable, but it's crucial to confirm this is what is happening. The 90A OCPD does not protect the 65A conductors.3. Coordination Study (Recommended)

For complex motor control systems, a coordination study is highly recommended. This study will analyze the time-current characteristics of all OCPDs to ensure proper coordination and selective tripping (the fault should trip the closest OCPD, minimizing the impact on other loads).4.

Consult an Electrical Engineer

If you are unsure about any aspect of this design, consult a qualified electrical engineer. Motor circuit protection can be complex, and it's crucial to get it right for safety and reliability.

Example Scenario

Let's say you have the following:

Control Panel Rating

53A (this is often a continuous duty rating, meaning the panel is designed to handle 53A continuously without overheating)

Upstream Breaker

60A

Conductors

65A rated

Motor FLA

40A (for example)

Motor Branch Circuit OCPD

90A (based on 175% of 40A FLA, roughly)In this scenario, if those 65A conductors are supplying other loads in addition to the motor circuit, you must have a 60A (or less) breaker protecting them before the motor branch circuit. If they are only supplying the motor branch circuit after the 90A fuses, then this setup is permissible. You need to verify which scenario you are in.

Important Note: This information is for general guidance only and should not be considered a substitute for professional electrical engineering advice or compliance with applicable codes and standards (NEC, etc.). Flag for review