You're right, the NEC doesn't specifically prohibit splicing Belden cables inside a junction box. However, there are several NEC articles that could be violated, depending on how you're splicing and what you're using the Belden cable for. Here's a breakdown

Why splicing Belden cables in a junction box might be illegal, and what NEC articles could apply:
1. Not Using Listed/Approved Methods & Materials (NEC 110.3(B))

This is a big one. Belden cables are often used for low-voltage control, data, or communications circuits. If you're splicing them with methods or materials not listed or not approved for that type of cable and its application, you're in violation. What this means in practice:

Don't use wire nuts

Wire nuts are almost always wrong for Belden cables, as they are primarily designed for solid core copper conductors. Belden cables are often small gauge and stranded, which wire nuts are often ineffective at gripping and can damage.

Don't use twist-and-tape

This is never an approved method in an electrical junction box.

Acceptable Methods (examples)

Properly sized and crimped connectors designed for that specific cable gauge and type (stranded). The crimping tool must also be the correct one specified for the connector. Small terminal blocks designed for low-voltage applications. Specialized splice kits designed for the cable type and application.

2. Improper Support/Securing of Cables (NEC 300.4, 300.11, 314.17)

Even if the splice is electrically sound, the cables entering the junction box need to be properly supported and secured to the box. If the Belden cables are just dangling or putting strain on the connections, it's a violation. Consider using cable clamps or appropriate strain relief connectors where the cable enters the box. The NEC requires that cables be secured to boxes so that there is no strain on the termination points.

3. Fill Requirements (NEC 314.16)

Junction boxes have specific fill requirements based on the wire size and the number of conductors. If the box is too small for the number of conductors and devices (including the splices and connectors), it's a violation. Belden cables are usually small, but multiple cables and bulky connectors can quickly fill a box. Be sure to correctly calculate the box fill based on the number of conductors and the volume taken up by devices, fittings, and equipment.

4. Identification of Conductors (NEC 310.11)

Ensure that the conductors within the Belden cables are properly identified, especially if they carry different signals or voltages. This is crucial for troubleshooting and future maintenance. Use appropriate labeling methods.

5. Communications Circuits (Chapter 8 of the NEC)

If the Belden cable is part of a communications circuit (e.g., network cable, telephone cable, audio cable), Chapter 8 of the NEC applies. This chapter has specific requirements for wiring methods, grounding, and bonding of communications systems. Article 800 is most commonly applicable.

6. Class 2 and Class 3 Circuits (NEC Chapter 9. Annex C)

If the Belden cable carries low voltage power limited current, then it is usually a Class 2 or Class 3 circuit. This has special wiring requirements, which is the gauge of the wiring, and insulation, the cable markings on the wire, and the voltage levels.

In Summary

The legality of splicing Belden cables in a junction box depends entirely on how it's done. You must use listed/approved methods and materials, adhere to box fill requirements, and properly support the cables. You should also make sure all the wiring meets the requirements in NEC Chapter 8. Always consult with a qualified electrician or electrical inspector if you're unsure about the proper way to splice these cables.

Disclaimer: I am an AI chatbot and cannot provide legal advice. This information is for general guidance only. Always consult with a qualified electrician or electrical inspector for specific code compliance questions. Flag for review