You have two requirements to consider, and you must satisfy both:1. Branch Circuit Overcurrent Protection (Fuse Size)

The fuse size dictates the minimum allowable conductor size.2.

Motor Full-Load Amps (FLA)

The conductor must be sized to carry at least 125% of the motor's FLA.Let's break it down using the NEC (National Electrical Code) as the governing standard, which I assume applies.

5 HP, 480V, 3-Phase Motor FLA

Refer to NEC Table 430.250. A 5 HP, 460V (480V is close enough) motor has an FLA of 7.6 amps.

Conductor Ampacity (125% of FLA)

7.6 amps 1.25 = 9.5 amps.

Branch Circuit Protection (30A Fuse)

This is where things get a little tricky.Now, to answer your specific questions:

Does the conductor from fuse to motor contactor have to be a minimum of 10 AWG because of the fuse size? Potentially, but not solely because of the fuse size. The fuse size impacts the allowable ampacity rating of the conductors. Or 125% of the motor load (7.6A) as small as 12-14AWG? Not likely.Here's the analysis and correct answer:1. Minimum Conductor Size Based on FLA (7.6A 1.25 = 9.5A)

You need a conductor rated for at least 9.5 amps. Consult NEC Table 310.16 (Ampacities of Insulated Conductors).
2.

Minimum Conductor Size Based on Overcurrent Protection (Fuse)

This is where you need to be very careful. While 12 AWG or 14 AWG might seem sufficient for the 9.5A, the 30A fuse can pose a problem.

NEC 240.4(D) Small Conductors

This section restricts overcurrent protection for small conductors. Basically, you can't protect a 14 AWG with a 30A fuse, and you generally can't protect a 12 AWG with a 30A fuse unless you meet specific conditions.

14 AWG Copper

Typically limited to a 15A overcurrent device.

12 AWG Copper

Typically limited to a 20A overcurrent device.Since you have a 30A fuse, you cannot use 12 AWG or 14 AWG unless an exception in 240.4(E) applies. Motor circuits have exceptions, but it's still crucial to verify.

Applying the Exception for Motor Circuits (NEC 430.22)

NEC 430.22 allows sizing motor branch-circuit conductors at 125% of the motor's full-load current. We've already established this requires at least 9.5A of ampacity.

Here's the key: You can use 14 or 12 AWG IF the motor itself has "inherent overload protection". This typically means that the motor has a thermal overload relay built into the motor controller. IF THAT IS THE CASE, you can protect the conductor using NEC 430.52(C)(1), allowing you to use up to 250% for an inverse time circuit breaker or 300% for a fuse. IMPORTANT

you MUST have the overload protection set at 125% of the motors FLC (7.6A) as per NEC 430.32(A)(1)

Conclusion


Verify Overload Protection

The first and most critical step is to verify if your motor has inherent overload protection. If it doesn't, you must use a larger conductor that can be protected by a 30A fuse.2.

If motor has internal overload protection

If the motor has a thermal overload (most motors do), then

12 AWG is likely sufficient. 14AWG is not sufficient. Be certain to follow NEC 430.52(C)(1).
3. If motor does NOT have internal overload protection

Use NEC 430.22(A) and 430.
52.

10 AWG would likely be the correct choice to handle the 30A fuse.

Therefore, most of the time 12AWG is sufficient, assuming the motor has overload protection, in which case you can go to 300% of the FLA and you still have a small fuse, so your conductors would be protected.Important Considerations



Conductor Insulation Type

The ampacity of a conductor depends on its insulation type (e.g., THHN, THWN). Use the correct ampacity from NEC Table 310.16 based on the insulation.

Temperature Rating of Terminations

Ensure the terminations (lugs, connectors) are rated for the conductor temperature.

Derating

Consider ampacity derating factors for ambient temperature and the number of conductors in a raceway (NEC 310.15).

Local Codes and Amendments

Always check for local electrical codes or amendments that might be stricter than the NEC.

Voltage Drop

While not directly related to safety, calculate voltage drop to ensure it's within acceptable limits.

Engineer Consultation

When in doubt, consult with a qualified electrical engineer to ensure proper and safe wiring practices.

Disclaimer: The information above is for general guidance only and should not be substituted for the advice of a licensed and qualified electrician or electrical engineer. Always follow applicable codes and regulations. Improper wiring can lead to fire, shock, and other hazards. Flag for review