No, it is not generally permissible to install two 14-2 NM-B (Romex) cables through a single knockout of a Carlon single-gang box using a standard connector. Here's why: Fill Capacity

Electrical boxes have specific fill capacity limits based on their size and the size and number of conductors entering them. Overfilling a box creates a dangerous situation because it prevents proper heat dissipation and can damage the conductors, leading to insulation breakdown, short circuits, and fire hazards.

Connector Ratings and Listings

Cable connectors are rated and listed for a specific number and size of conductors. Most standard NM cable connectors are designed and listed for

one cable per knockout/entry point. Trying to jam two cables into a connector designed for one puts undue stress on the connector, might damage the cables, and violates the connector's listing.* Code Compliance (NEC - National Electrical Code)

The NEC provides regulations for the proper installation of electrical systems, including box fill calculations and proper connector usage. Violating box fill rules and connector listings is a code violation.

What you're likely seeing and why it's (potentially) wrong

You've likely seen electricians (and others) do this. It's a shortcut, and while it might "work" in the short term, it's not the right way to do it and can create long-term problems.

Acceptable Alternatives


Use a Larger Box

If you need to run that many cables, use a deeper or wider box (e.g., a larger single-gang box or a two-gang box) that can properly accommodate the number of conductors and cables. Calculate the box fill according to the NEC to ensure compliance.2.

Ganged Boxes

If you have multiple circuits in a small area, consider using multiple single-gang boxes joined together.3.

Use Appropriate Connectors

Some connectors are specifically designed to accommodate multiple cables in a single knockout. These connectors are typically more expensive and less common, but they are the correct solution if you need to do this safely and legally.

Important

Make sure the connector is listed for the specific type and size of cables you're using and that it's properly installed.

In Summary:

While it might seem convenient to run two cables through one knockout, it's generally not permitted due to box fill restrictions, connector limitations, and code compliance issues. Doing so is a safety hazard and can lead to electrical problems. Always follow proper electrical practices and consult the NEC and local codes to ensure a safe and code-compliant installation. When in doubt, consult with a qualified electrician. Flag for review