You're right, running both low voltage and line voltage in the same enclosure generally violates electrical codes. Let's explore some code-compliant and neat methods for installing tape light transformers in residential settings.

Understanding the Code Issues Separation of Voltages (NEC 725.136)

The National Electrical Code (NEC) generally requires the separation of Class 2 (low voltage, often used for tape lighting) and Class 1 (line voltage) circuits. This is to prevent the possibility of a fault on the line voltage side from energizing the low-voltage wiring. While the exact wording of the relevant articles might change slightly between code cycles, the intent remains consistent: keep the voltages separate.

Listing and Labeling (NEC 110.3)

Any equipment used must be listed and labeled for the specific purpose it's being used for. This includes junction boxes, wiring methods, and the transformer itself.

Code-Compliant Installation Methods

Here are some approaches, along with considerations and best practices:1.

Dedicated Recessed Box (with barriers)



Description

This is the cleanest looking method, but requires using a specific type of recessed box designed for low and high voltage separation.

How it works

These boxes have a physical barrier or divider inside to create two separate compartments. One side is for line voltage wiring, and the other is for low-voltage wiring and the transformer.

Advantages

Neat, hides everything in the wall.

Disadvantages

Can be more expensive. Requires careful selection of a box that is specifically listed for this purpose. Make sure it's large enough for the transformer and wiring without overcrowding. The barrier MUST be maintained – knockouts and entries need to be done carefully.

Code Compliance

If the box is specifically listed for mixed voltage use and the barrier is maintained, this can be code-compliant. Inspect the box for clear markings.

Caution

Never modify a standard electrical box by adding your own divider. This will not be code-compliant.2.

Two Separate Boxes (Preferred Method)



Description

The most common and generally easiest way to ensure code compliance.

How it works

Install a standard electrical box (e.g., 4" square with a mud ring) for the line voltage connection. Run your line voltage wiring into this box. Terminate to a receptacle or a set of wires. Locate a separate, nearby low-voltage enclosure. Run the low-voltage wiring from the transformer (plugged into the receptacle in the line voltage box, or hardwired to the wires in the line voltage box) to the tape lights.

Advantages

Simple, straightforward, and easy to inspect. Minimizes any question of code compliance.

Disadvantages

Requires two boxes.

Variations



Transformer on top of cabinet

Line voltage box behind the cabinet. The low-voltage wires run to the transformer sitting on top of the cabinet (often done for under-cabinet lighting).

Remote Transformer

Put both boxes in a less conspicuous location (like a basement or closet). Run low voltage wires longer distances.3.

Surface-Mounted Enclosure



Description

Use a surface-mounted enclosure that is large enough to house both the line voltage wiring and the transformer.

Advantages

Easier to install in existing construction than a recessed box. Good for areas where in-wall space is limited.

Disadvantages

Visible on the wall.

Code Compliance

Similar to the recessed box, you must ensure the enclosure is listed and labeled for mixed-voltage use. Internal barriers or partitions may be required.4.

Transformer Location Considerations Accessibility

NEC 450.13 requires transformers to be readily accessible unless they are dry-type transformers rated not over 50VA. While many tape light transformers are low VA, it's still good practice to make them accessible for maintenance or replacement. Putting them behind drywall without an access panel is a bad idea.

Ventilation

Transformers generate heat. Ensure adequate ventilation to prevent overheating.

General Best Practices



Read the Transformer Instructions

Always follow the manufacturer's instructions for the transformer regarding wiring, mounting, and ventilation. This is crucial for safety and warranty purposes.

Wire Sizing

Use appropriate wire gauges for both line voltage and low voltage wiring. Refer to the NEC for ampacity ratings. Low voltage wire gauge is especially important for long runs to prevent voltage drop.

Connections

Use proper wire connectors for all connections. Wire nuts for line voltage, and appropriate connectors for low voltage. Don't rely on twisting wires together.

Strain Relief

Provide strain relief for all wires entering and exiting boxes and enclosures. This prevents stress on the connections.

Labeling

Label the low-voltage wiring clearly to indicate its purpose and voltage.

Inspection

If you're unsure about any aspect of the installation, consult with a qualified electrician and have your work inspected.

Why the Guy's Method is Problematic (Without a Listed Box)

The method you described, of putting everything into a standard electrical box without a listed divider, is generally not code-compliant because it violates the separation of voltage requirements. Even if the transformer is insulated, it doesn't guarantee sufficient isolation in the event of a fault.

Example Scenario (Under Cabinet Lighting)

1. Install a standard single-gang electrical box behind the upper cabinet.
2. Run NM cable (Romex) to the box and terminate to a receptacle outlet.3. Plug the tape light transformer into the receptacle.
4. Drill a hole (with a bushing or strain relief) in the cabinet floor near the back.5. Run the low-voltage wiring from the transformer down through the hole to the tape lights.
6. Secure the wiring neatly under the cabinet.

In Summary:

While a single recessed box can* be a clean solution, it's essential to use a box specifically designed and listed for mixed-voltage applications. Otherwise, separating the line voltage and low-voltage connections into two separate enclosures is the safest and most reliable way to ensure code compliance. Always prioritize safety and consult the NEC and manufacturer's instructions for proper installation practices. Flag for review