You're right to be cautious about mixing low voltage and line voltage wiring in a gutter or enclosure! Here's a breakdown of the rules and considerations, specifically focusing on your pool application

National Electrical Code (NEC) Rules & Why They Matter
NEC Article 300.3(C)(1) - Mixing Voltages

Generally prohibits conductors of different voltage systems (e.g., low voltage and line voltage) in the same raceway, cable, or enclosure unless certain conditions are met.

Exception No. 1

Where the primary and secondary circuit conductors of a transformer are installed in a single enclosure. This is very specific to transformers.

Exception No. 2

Class 1, Class 2, and Class 3 circuits are permitted to be installed together where they are functionally associated.

Exception No. 3

Fire alarm circuits can be mixed under certain conditions.

Exception No. 4

Communications circuits and network-powered broadband communications circuits are permitted to be installed in the same cable, enclosure, cable tray, raceway, or cable routing assembly.

Exception No. 5

Where the conductors are separated by a barrier.

Exception No. 6

Low voltage lighting systems are permitted to be installed with line voltage conductors, when they are separated by a barrier.

NEC Article 680 (Swimming Pools, Fountains, and Similar Installations)

This is the governing article for your pool wiring. It has specific requirements related to separation, bonding, grounding, and approved equipment. Article 680 is your primary concern.

Why Separation is Important



Safety

Prevents accidental contact between high-voltage and low-voltage circuits. A short circuit could energize the low-voltage wiring, creating a shock hazard.

Insulation Breakdown

Prolonged exposure to higher voltages can degrade the insulation of low-voltage wires, leading to shorts or ground faults.

Electromagnetic Interference (EMI)

High-voltage circuits can induce unwanted currents or signals in low-voltage circuits, disrupting their operation.

Can You Mix the Wiring in a Gutter/Enclosure for Your Pool?

The answer is generally NO, unless. You need to carefully evaluate if the exceptions allow it in your specific situation.Here's a breakdown of considerations:1. Low Voltage Control Wiring

You mentioned "low voltage control stuff." What specifically is this controlling? Pool lights? Pumps? If it's integral to the pool equipment and considered part of a listed pool control system, it might be permissible. However, the burden of proof lies with you to demonstrate compliance with the NEC and the equipment listings.2.

Voltage Rating of Low-Voltage Wiring

You mentioned the low-voltage wiring is rated for 300V. That's a good start, but it doesn't automatically allow mixing. The NEC is more concerned with the separation of voltage classes rather than just the insulation rating.3.

Barriers

The exception regarding barriers is your most likely solution to meeting code if you want to combine. You could build a permanent, robust barrier within the gutter to physically separate the high-voltage and low-voltage sections. The barrier must be made of an approved non-conductive material and be securely fastened.4.

Listed Equipment and Instructions

ALWAYS follow the manufacturer's instructions for any pool equipment. If the equipment is listed and labeled, it will indicate how the wiring should be handled.

Solar Wiring and Pool Wiring: Not Directly Comparable

You asked about solar wiring. Yes, it's generally permissible to mix AC and DC wiring in solar PV systems within specific, listed combiner boxes or enclosures designed for that purpose. Article 690 covers solar PV systems and has its own specific rules. Key Difference

Solar PV combiner boxes and enclosures are specifically designed and listed for safely mixing AC and DC voltages. They have proper insulation, separation, overcurrent protection, and labeling. A generic gutter or enclosure is not the same thing.

Listing is Key

Just because solar wiring can be mixed in certain situations doesn't mean pool wiring can be treated the same way. The listing of the equipment is critical.

Best Practices and Recommendations1. Consult a Licensed Electrical Inspector

This is essential. A licensed electrical inspector is the authority having jurisdiction (AHJ). They will interpret the NEC and local codes and make the final determination on whether your wiring is compliant. Call them before you do any wiring.2.

Separate Enclosures

The safest and often easiest solution is to use separate enclosures for your low-voltage and line-voltage wiring. This completely avoids the mixing issue.3.

Dedicated Raceways

Run separate conduits for your low-voltage and line-voltage wiring all the way back to the source panels.4.

Professional Installation

Consider hiring a qualified electrician experienced in pool wiring. Pool wiring is safety-critical, and mistakes can have serious consequences.5.

Clear Labeling

If you are able to use a gutter with a barrier, clearly label each section (e.g., "120V AC Wiring," "Low Voltage Control Wiring") to avoid confusion during future maintenance.

Example Scenario (Likely Compliant if Done Correctly)

Let's say you have low-voltage wiring for controlling LED pool lights. These lights are part of a listed pool lighting system. The manufacturer's instructions specifically allow mixing the low-voltage wiring with the line-voltage wiring within a provided control box that is listed for that purpose. Even in this case, you would need to follow the instructions precisely.

In Summary

Don't assume you can mix low-voltage and line-voltage wiring in a general-purpose gutter or enclosure for your pool. The NEC has strict requirements for separation. Consult a licensed electrical inspector, follow the manufacturer's instructions for all equipment, and prioritize safety. Using separate enclosures or a gutter with a proper barrier are the most common and safest approaches. Flag for review