You're on the right track, and your friend's customer's situation is common. 4160V installations always require careful consideration of the code. Here's a breakdown of the issue and applicable code sections, along with factors to consider

You are generally correct. 300.37 allows for other raceways but with critical caveats.

Key Code Sections and Considerations



300.37 Raceways Exposed to Different Temperatures. This is the primary article governing your situation. It does permit the use of raceways other than rigid metal conduit, intermediate metal conduit, or electrical metallic tubing. However, it's not a blanket allowance. The keyword is "identified." Let's break that down: "Identified" Definition (Article 100)

"Suitable for the specific purpose, function, use, environment, application, etc., where described in a particular Code requirement." This means the Sealtite and its fittings must be listed and labeled for use with 4160V and in the specific environment it's installed in. This information should be readily available from the manufacturer's literature.

The Manufacturer's Instructions are KEY

The sealtite needs to be approved for over 600 Volts. The specifications for the wire insulation needs to be at least that rated voltage.

300.3(C)(1) Conductors of the Same Circuit

"All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, cable armor, or cable sheath, unless otherwise permitted in 300.3(C)(1) through (C)(4)." This is important for minimizing inductive reactance and potential voltage drop, especially in medium voltage circuits. Sealtite inherently offers less magnetic shielding than rigid conduit. While it may not be a direct violation in the short run, it's good practice to keep the Sealtite section as short as possible.

399.4 Other Articles

Article 399 Supplemental Wiring for elevators and other similar equipment.

250 Grounding and Bonding

Ensuring proper grounding and bonding of the Sealtite is paramount for safety. Verify the fittings used are listed for grounding and bonding purposes.

356.12 Uses Not Permitted

Article 356 is the article that covers Liquidtight Flexible Nonmetallic Conduit: (LFNC) You need to read this article carefully because it lists conditions under which this type of raceway is not permitted, such as being subjected to physical damage, or the ambient temperature being higher than what the product is rated for.

Manufacturer's Listing and Instructions

This is probably the most important aspect. The specific Sealtite and fittings MUST be listed (e.g., UL-listed) for the voltage (over 600V), the environment (wet, dry, corrosive, etc.), and the application (connecting to equipment). Look for specific voltage ratings printed on the product itself and in the manufacturer's literature.

Practical Considerations & Questions to Ask


Manufacturer's Documentation

Does the Sealtite manufacturer explicitly state that their product is suitable for 4160V applications? Get this in writing (datasheet, catalog cut sheet). Don't rely on verbal assurances.2.

Environment

What are the environmental conditions? Is it wet, corrosive, subject to vibration, etc.? The Sealtite needs to be rated for those conditions.3.

Mechanical Protection

How vulnerable is the Sealtite run to physical damage? Rigid conduit offers superior protection. If there's a risk of damage, the Sealtite run needs to be well-protected.4.

Fitting Compatibility

Are the fittings used specifically designed and listed for the Sealtite being used, and are they rated for 4160V? Improper fittings can compromise the integrity of the system.5.

Inspection Authority (AHJ)

Ultimately, the Authority Having Jurisdiction (inspector) has the final say. Discuss the proposed installation with them before the work is done to get their approval and address any concerns they might have. Documentation from the manufacturer will be crucial.

Why the Rigid to Sealtite Transition is Common

The transition from rigid to Sealtite is frequently done to:

Reduce Vibration Transfer

Sealtite can help isolate the gear from vibration in the rigid conduit system.

Provide Flexibility for Alignment

It simplifies connecting to equipment that may have slight misalignments.

In Conclusion:

Using Sealtite on a 4160V system can be code-compliant, but it requires careful adherence to the NEC, specific product listings, and a thorough understanding of the application. The electrician needs to demonstrate that the Sealtite and fittings are "identified" for the voltage, environment, and intended use, and that all other relevant code requirements are met. Don't assume anything. Document everything. And get AHJ approval before installation.I hope this helps! Good luck! Flag for review