Let's break down the code requirements and what you're proposing to make sure everything is safe and compliant. You're on the right track, but there are a few crucial points to clarify.

Key Concepts and NEC Rules



Ampacity

The maximum current a conductor can carry continuously without exceeding its temperature rating.

Overcurrent Protection

A circuit breaker protects the wiring from overheating and potentially causing a fire. The breaker's amperage rating should never exceed the ampacity of the wiring.

Continuous Load

A load that operates for 3 hours or more. EV chargers are considered continuous loads. NEC requires you to size the wiring and overcurrent protection at 125% of the continuous load.

Temperature Ratings

Wiring is rated for specific temperatures. You must use the correct ampacity column in the NEC tables based on the lowest temperature rating of any termination point (breakers, receptacles, etc.).

SEU Cable

Service Entrance Cable, Underground. Typically used for the main power feed to a building. SEU cable typically has a 75°C insulation rating.

NM-B Cable (Romex)

Nonmetallic-sheathed cable. Romex cable is typically rated for 60°C.

Terminations

Most breakers and receptacles are rated for 75°C terminations. Always confirm.

Your Scenario (Tesla Charger at 48 Amps)


Continuous Load Calculation

48 amps (charger setting) 1.25 = 60 amps. This means your wiring and breaker need to be rated for at least 60 amps.2.

Breaker Size

You want to use a 60 amp breaker. This is acceptable because it protects the wiring from overcurrent and the 60 amp breaker is sized at 125% of your 48 amp charger.3.

Wire Size and Ampacity

You are considering 6-6-8 CU SEU cable.

75°C Column

Assuming your breaker and receptacle are rated for 75°C connections, then yes, you can use the 75°C column in NEC Table 310.16 (or your local equivalent).

6 AWG Copper

According to the 75°C column in the NEC Table 310.16, 6 AWG copper wire is rated for 65 amps.
4.

Suitability of SEU Cable

You are correct that one of the differences is the insulation. SEU cable is usually rated for higher temperature which allows it to be used in the 75° column.

So, let's put it all together



Charger Setting

48 amps

Breaker

60 amp (Calculated for a continuous load of 60 amps (48 1.25))

Wiring

6-6-8 CU SEU Cable

Temperature Rating

Using the 75°C column.

6 AWG Copper Ampacity

65 amps (exceeds the continuous load requirement)

Yes, in this scenario, using 6-6-8 CU SEU cable on a 60 amp breaker for a 48 amp Tesla charger is compliant with the NEC code if your termination points are rated for 75C.

Important Considerations and Potential Issues



Local Codes and Permits

Always check with your local electrical inspector for specific requirements in your area. They may have stricter rules or interpretations of the NEC.

Voltage Drop

For long runs, calculate voltage drop to ensure the charger receives adequate voltage. Undersized wiring can cause voltage drop, leading to slow charging or even damage to the charger.

Professional Installation

It is highly recommended to have a qualified electrician perform the installation. They will be familiar with local codes and ensure the installation is safe and compliant.

Grounding

Make sure you have a proper grounding conductor run with the circuit. The #8 is likely for the ground wire.*

Mechanical Protection

Protect the cable from physical damage where it is exposed.

In summary, your analysis appears correct, BUT you MUST confirm the temperature ratings of your breakers and the device terminals, and follow all local codes and permit requirements. It is strongly recommended to hire a qualified electrician. Flag for review