Okay, let's break down this conversion and see what potential issues an inspector might raise

Potential Issues & Code Concerns

1. 8/2 Romex Ampacity

This is the biggest point of contention. 8/2 Romex (NM-B cable) has an ampacity of

40 amps at 60°C (100°C/194°F) in most typical residential installations. You are feeding it with a 60 amp breaker which is a code violation. NEC 334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be in accordance with 310.
15. The allowable ampacity of Types NM, NMC, and NMS cable shall not exceed that of a 60°C (140°F) conductor.

Why this is a problem

Overcurrent protection is meant to protect the wire. A 60A breaker will allow the 8/2 cable to overheat, potentially causing a fire before the breaker trips.

Solution Required

You MUST downsize the breaker at the main panel to

40 amps to protect the 8/2 cable.2.

Neutral Configuration

Your plan for the neutral at the main panel is incorrect and

extremely dangerous. You can't simply repurpose the neutral conductor in the existing 8/2 cable as a ground and expect to use it as a neutral.

Why this is a problem

The neutral must be kept as a neutral the entire distance from the subpanel back to the main panel. If you bond it to ground at the main panel, you're creating a parallel ground path. Any neutral current on the circuit now has the potential to flow through the grounding system, creating a shock hazard. This is known as a "neutral-ground fault" and can energize any grounded metal parts connected to the system (conduit, appliance housings, etc.).

Solution Required



Do NOT bond the neutral at the main panel. The neutral conductor of the 8/2 cable MUST land on the neutral bus of the main panel.

The Hot Conductor of the 8/2 cable Must be removed from its original 2-pole breaker and land on a new single pole breaker.3.

Subpanel Bonding/Grounding

Your description sounds generally correct for a detached subpanel, but let's clarify to ensure compliance with NEC 250.32:

Neutral-Ground Separation

In the subpanel, the neutral bus

must be isolated from the enclosure and from the ground bus. This is typically accomplished by removing the bonding screw or strap that connects the neutral bus to the panel enclosure.

Ground Bus

The ground wire from the 8/2 cable is connected to a separate ground bus, bonded to the subpanel enclosure.

No Equipment Grounding Conductors

The only ground conductor connected to the subpanel will be the ground conductor from the existing hot tub feeder. All branch circuits originating at the subpanel will need to be run with a equipment grounding conductor (either a bare copper conductor or a conductor with green insulation)

Verify the Subpanel is Rated as Suitable for Use as Service Equipment Service equipment must be marked in accordance with NEC 408.3(C) to ensure it is suitable for use as service equipment.
4.

Single Pole Breaker in a 2-Pole Slot

Filling an empty slot in the panel with a single-pole breaker when a two-pole breaker was removed might not be permissible. Check the panel's labeling. Some panels don't allow this.5.

Load Calculation vs. Wire Size

While your estimated load is 55A, you MUST perform a proper load calculation according to Article 220 of the NEC. This goes beyond simply adding up the breaker sizes. You need to consider things like demand factors, square footage, appliance loads, etc. Even if your calculated load is less than 40A, the inspector may still object to feeding an estimated 55A of load through a 40A cable. If a load is going to exceed the wire size by 15 amps it would be more prudent to find another wiring option for the sub panel.6.

Ground Fault Circuit Interrupter (GFCI) Protection



Basement Receptacles

Receptacles in finished basements always require GFCI protection per NEC 210.8(A)(5). This means you'll need to install GFCI breakers in the subpanel for the 15A and 20A receptacle circuits, or use GFCI receptacles as the first outlet on each circuit.

Lighting

Check local codes for GFCI requirements for lighting in basements. Some jurisdictions may require it.7.

Arc Fault Circuit Interrupter (AFCI) Protection

Most jurisdictions require AFCI protection for branch circuits in dwelling units per NEC 210.12. This typically means using AFCI breakers for the new circuits.
8.

Working Space

Ensure you have adequate working space around the subpanel as required by NEC 110.26. This includes sufficient depth, width, and headroom.
9.

Overfilled Raceway

It is highly likely that the original raceway has too many conductors for the raceway size. The NEC allows a certain percentage of conductors in the raceway based on the raceway size. Section 314.16(A) for box fill calculations and 314.16(B) for conductor fill calculations.

Revised Plan (Based on Correcting the Above Issues)1.

Main Panel

Remove the old 60A 2-pole breaker. Install a

40A single-pole breaker to protect the 8/2 NM-B cable. Connect the hot conductor from the 8/2 cable to the 40A breaker. Connect the neutral conductor from the 8/2 cable to the neutral bus. Connect the ground conductor from the 8/2 cable to the ground bus.2.

Subpanel



Isolate the neutral bus from the subpanel enclosure. Remove the bonding screw/strap if present. Connect the hot conductor from the 8/2 cable to one of the hot buses. Use a jumper if necessary to feed both buses. Connect the neutral conductor from the 8/2 cable to the isolated neutral bus. Install a separate ground bus, if one is not already present. Connect the ground conductor from the 8/2 cable to the ground bus. Run new branch circuits from the subpanel, including a ground wire in each circuit. Use GFCI breakers or receptacles where required by code. Use AFCI breakers where required by code.

Important Considerations

Communicate with the Inspector

Talk to your local electrical inspector before you start the work. Explain your plan and ask for their input. They may have specific requirements or interpretations of the code that you need to follow.

Documentation

Keep a record of your load calculations and any conversations you have with the inspector.

Safety First: Always de-energize the circuits before working on them. Use proper safety equipment (PPE, voltage testers, etc.).By addressing these points, you should be able to create a safer and code-compliant subpanel installation. The biggest hurdles are the wire ampacity and the need to maintain a proper neutral and ground system. Good luck! Flag for review