You've identified the key issues correctly: the 360-degree rule, Romex ampacity limitations, and the need for 55A at 240V. Here's a breakdown and some suggestions

Addressing Your Concerns and Options
Romex (NM-B) is a Problem

You're absolutely right about the ampacity limitations. While 6/3 or 6/4 Romex might seem appropriate at first glance, it's limited by the 75°C column and won't handle a continuous 55A load safely and legally.

360-Degree Bend Rule (NEC 314.22)

This is a real hurdle. If you exceed 360 degrees of bends between pull points, you're in violation. It makes a continuous run of conduit very difficult.

SER Cable as an Option

This is a viable option and likely your best bet given the constraints.

SER Cable and Ampacity

SER (Service Entrance Cable) is typically used as service entrance conductors. While it can be used for feeders, and in your case a branch circuit, its ampacity must still be considered. The ampacity is determined based on the same factors as NM-B cable – conductor size, insulation type, and ambient temperature, and in your case, is based on the 75C column.

SER Cable Size

This is crucial. To handle 55A continuously and meet code requirements, you'll need to select an SER cable size that accommodates this load after derating. You'll likely need #4 AWG Aluminum, which is rated for 60A at 75C.

Grounding with SER

SER cable typically has a bare ground wire. This will serve as the equipment grounding conductor.

Alternative Approaches and Considerations



Subpanel in the Attic

This is probably the best solution if feasible. Install a small subpanel in the attic, fed by appropriately sized conductors from the main panel. Then, you can run a short run of conduit or appropriately rated cable to the steam shower. This offers several advantages: Reduces voltage drop over the long run. Future-proofs for additional attic loads. Simplify compliance with the 360-degree bend rule for the final run to the steam shower. You would run a larger feeder circuit to the attic subpanel, potentially using larger gauge wire in conduit or aluminum wire in conduit to reduce costs. Consult with an electrician on the feeder size.

Relocating the Main Panel

Probably impractical, but worth mentioning. If moving the main panel is an option, it could simplify everything.

Alternative Routing

Could you explore other possible routes, even if they seem unconventional? Consider outside walls, under floors, etc. If possible it may be worth exploring.

Offset Bends and Pull Boxes

While difficult, carefully planned offset bends and strategically placed pull boxes might allow you to minimize the number of bends between the main panel and the steam shower, thus satisfying the 360-degree rule. This will require precise measurements and planning.

Specific Recommendations and Steps1. Consult with a Licensed Electrician

This is paramount. They can assess the specific conditions of your home, perform load calculations, and ensure compliance with all applicable codes. They can also advise on the practicality and cost of each option.2.

Evaluate the Subpanel Option

This is highly recommended. Get a quote for installing a small subpanel in the attic. This will likely be the safest and most future-proof solution.3.

Calculate Ampacity Derating

Regardless of your wiring method, you must account for ambient temperature. Attics can get very hot, which can significantly reduce the ampacity of conductors. Use the appropriate derating factors from the NEC to ensure your chosen conductor size can handle the load under the worst-case temperature scenario.4.

Check Local Codes

Local codes may be stricter than the NEC. Always defer to the local authority having jurisdiction (AHJ).5.

SER Cable Installation

If you go with SER: Choose the correct size cable, most likely #4 AWG Aluminum. Properly secure the cable using appropriate supports. Ensure the cable is protected where it passes through framing members. Terminate the cable correctly at the main panel and at the steam shower unit. Use appropriately sized circuit breakers.6.

Grounding

Ensure your steam shower unit is properly grounded using the grounding conductor within the SER cable.

Important Safety Notes



Electricity is dangerous. If you are not a qualified electrician, do not attempt this work yourself. Always de-energize circuits before working on them.* Use appropriate PPE (personal protective equipment) when working with electricity.

In Summary

The subpanel in the attic is likely the best approach. If that's not feasible or too expensive, using properly sized SER cable is a viable alternative, but you

must consult with a licensed electrician to ensure compliance with all applicable codes and safety standards. Don't compromise on safety! Good luck! Flag for review