You're proposing a "conduit sleeve" approach, housing multiple conduits within a larger conduit. Here's a breakdown of the code implications and potential technical issues regarding your proposal

Key NEC (National Electrical Code) Considerations:
300.3(C) Conductors of Different Systems. This is the most relevant section. It generally prohibits conductors of different systems (AC power, DC power, and communication) in the same raceway, cable, or enclosure. However, there are exceptions. Exception No. 1

Where all of the conductors are insulated for the maximum voltage of any conductor in the raceway or cable. This is unlikely to apply, as communication cables often have lower insulation voltage ratings.



Exception No. 2

Section 725.136(I) for Class 2 and Class 3 remote-control, signaling, and power-limited circuits shall be permitted to be installed in the same cable, enclosure, or raceway. This is unlikely to apply as it would require the low voltage communication wiring to fall under that class.

Exception No. 3

Grouping of conductors as permitted in 690.4(B) shall be permitted. This does not apply as these are not PV sources.



Exception No. 4

Grouping of conductors as permitted in 727.6 shall be permitted. This is for instrumentation tray cable.

Exception No. 5

As permitted in 725.48. This is for PLTC Cable.

300.17 Number and Size of Conductors in Raceway

This section dictates conduit fill limits. While you're dealing with conduits within a conduit, the aggregate fill of the inner conduits becomes relevant, potentially affecting heat dissipation.

310.15 Ampacity

Conduit fill affects the allowable ampacity of conductors due to heat build-up. While the outer conduit doesn't directly contain the conductors, closely packed inner conduits can still raise the operating temperature of the conductors within. You'll need to carefully consider the ampacity derating factors in 310.15(C) and associated tables.

310.16 Allowable Ampacities of Insulated Conductors

If your fill is higher than the allowable amount, this may affect the ampacity rating of the wires inside the conduit.

Chapter 9, Notes to Tables

These notes cover conduit fill calculations and adjustments to ampacity.

110.12 Mechanical Execution of Work

The installation must be done in a neat and workmanlike manner. Cramming too many conduits into a larger one could violate this.

Technical Issues to Consider



Heat Dissipation

Multiple conduits packed tightly together reduce the ability of each conduit to dissipate heat. This is especially problematic for the AC and DC power conduits, where conductors carrying significant current will generate heat. Overheating can degrade insulation and reduce conductor lifespan.

Accessibility

Future access for maintenance or repairs becomes much more difficult. You'd have to pull all the inner conduits out to work on any one of them.

Future Expansion

Filling the large conduit now limits future expansion possibilities.

Communication Cable Interference

While not a certainty, running communication cables near power cables can introduce noise and interference, degrading signal quality, especially if the outer conduit is metallic and not properly grounded.

Conduit Fill

As mentioned above, this could be too much fill for the large RGS conduit

Why the Proposal is Likely Problematic

The primary issue is

NEC 300.3(C). Putting AC, DC, and communication conductors in the same raceway (which is what the outer RGS conduit effectively becomes) generally violates this rule unless you can meet an exception. Meeting the exceptions are generally not feasible unless all the conductors have the same insulation rating, even the low-voltage communication wiring.

Alternatives & Recommendations


Separate Conduits

This is the most straightforward and generally the best approach. Run separate RGS conduits for each system (AC, DC, communication). This ensures compliance with 300.3(C), simplifies maintenance, and improves heat dissipation.
2.

Physical Separation within a Trench

If aesthetics are the concern, bury the separate conduits in the same trench but with adequate physical separation (e.g., using duct banks or spacers).3.

Consider an External Conduit Sleeve

While technically still a sleeve, using a much larger diameter sleeve (e.g., a concrete encasement or large diameter corrugated pipe) primarily for physical protection and not as a raceway itself might be acceptable. This would require careful consideration and local AHJ (Authority Having Jurisdiction) approval. The inner conduits would still be treated as separate raceways.

Crucial Step: Consult the AHJBefore proceeding with any design involving multiple conduits in a shared sleeve,

consult with the local Authority Having Jurisdiction (AHJ). They have the final say on whether your proposed installation meets code requirements and is safe. Provide them with detailed drawings, conductor sizes, ampacities, and communication cable specifications.

In Summary

Your proposed approach of placing separate AC, DC, and communication conduits inside a single, larger RGS conduit is

likely not compliant with the NEC and raises potential technical concerns. Prioritize separate conduits as the preferred solution and always consult with the AHJ. Flag for review