This is a very interesting and pertinent question, especially with the rise of mass timber construction. Your understanding is largely correct, and this is a viable method, but there are a few crucial points and considerations to keep in mind. Let's break it down

Your Understanding and Code Compliance:
Article 300.18(A) - Raceway Installation Complete

Yes, you're spot on. The general intent of this section is that raceways should be fully installed before pulling conductors. This eliminates the potential for damage to conductors during installation of the raceway itself.

Article 362.30 - Securing and Supporting ENT

Absolutely. Proper support of the ENT is essential to prevent it from being displaced during the concrete pour and vibration.

Terminating at Both Ends

This is key. The ENT must be terminated at both ends with appropriate fittings (connectors) to junction boxes or other approved terminations. This protects the conductors from moisture and debris entering the system during the concrete pour.

Key Considerations and Potential Challenges


Concrete Vibration

This is the biggest risk. Concrete vibrates aggressively during the pour to consolidate the mix and remove air pockets. This vibration can shift the ENT, especially if it isn't securely fastened.

Solution

Over-engineer your supports. Use more supports than the minimum required by 362.30. Consider using metal straps/ties in addition to the listed ENT supports to provide extra resistance to movement. Coordinate with the structural engineer or concrete contractor regarding the vibration plan and consider isolation techniques.
2.

Concrete Pressure

The weight of the wet concrete can crush or deform the ENT, especially if the concrete mix is particularly dense or the pour is deep.

Solution

Use appropriately sized ENT (consider heavier wall ENT) and ensure proper support spacing. Also, consider the depth of the concrete pour and whether additional reinforcement is needed for the ENT itself.3.

Water/Moisture Intrusion

Concrete is very alkaline and can damage some types of wire if it comes into direct contact.

Solution

Make sure your terminations are completely sealed. Consider using liquid-tight connectors or wrapping the connectors with electrical tape. The conductors chosen need to be rated for a wet environment.4.

Coordination with Other Trades

Your electrical runs need to be meticulously coordinated with other trades (plumbing, HVAC, structural). You don't want your ENT runs to conflict with reinforcement or other embedded items.

Solution

Early and frequent communication with all involved parties is crucial. Use BIM (Building Information Modeling) if available to identify potential conflicts.5.

Box Placement/Access

Ensure that the location of the boxes at each end of the ENT run is accurate and accessible after the concrete pour. The top surface of the box should be flush with the finished floor.6.

Rodent Protection

Since ENT is a non-metallic product, it is easier for rodents to chew through. Consider how you will maintain the integrity of the system and protect it from rodents chewing.7.

Inspection

Inform the local electrical inspector of your intent. They may have specific requirements or concerns based on local conditions and practices. Documentation is crucial.8.

Termination Access

Make sure your terminations (boxes) are sized appropriately for the number of conductors and devices. This will need to be calculated before the concrete pour and cannot be changed afterward.

Recommendations



Detailed Drawings

Prepare detailed drawings showing the location and routing of all ENT runs, support locations, and box placements.

Mock-up

Consider building a small mock-up section to test your installation techniques and ensure the ENT can withstand the concrete pour.

Inspection Before Pour

Have the electrical inspector and the general contractor inspect the ENT installation before the concrete pour.

Photo Documentation

Take extensive photos of the ENT installation before the concrete pour. This provides a record of the routing and support locations, which can be helpful if any issues arise later.

Consider Flexible Metal Conduit (FMC)

If you have concerns about the ENT being crushed during the concrete pour, consider using FMC instead. While it's more expensive, it's much more robust. You would need to follow the same securement and termination guidelines.

In Conclusion:

Installing ENT before the concrete pour is a viable option for this project, provided you pay very close attention to the details outlined above. Over-engineering the supports, ensuring proper termination, and meticulous coordination are key to success. Don't hesitate to consult with a structural engineer or concrete specialist for advice on how to mitigate the risks associated with concrete vibration and pressure. Good luck! Flag for review