NFPA 731 Section 4.6.3.1 requires the installation of all wiring, cable, and equipment to be performed in accordance with NFPA 70 (NEC), Article 725 or Article 800, where applicable. Many circuits in a security system are “signal circuits” and NEC^® Article 725 must be followed.

A common question is whether a box is needed to enclose splices in Class 1, 2 or 3 remote- control, signaling, and power-limited circuits. Rarely are Class 1 circuits used in security system installations. Class 2 and 3 circuits are much more common in security system wiring. The general rules on enclosing conductor splices in a box or other enclosure come from Part 1 of NEC^® Article 300, Section 300.15.

NEC 725.3 states that “only those sections of Article 300 referenced in this article shall apply to Class 1, Class 2, and Class 3 circuits”. That being said, the portion of NEC^® Section 300.15 that requires splices to be in a box only applies to Class 1 circuits as mentioned in 725.46. Nothing is mentioned in Article 725 regarding compliance with NEC^® 300.15 for Class 2 or 3 circuits other than Section 725.3(K) which requires a bushing to protect cables as they emerge from a raceway in compliance with 300.15(J).

If Class 1 circuits are used in the security system and splices are made, the splices must be enclosed in a box or other acceptable enclosure. If Class 2 or 3 circuits are used in security system wiring, no junction box is required but the splice cannot simply be twisting the conductors together and covering them with electrical tape. The splicing devices used must comply with NFPA 731 Section 4.6.3.3 which requires security system conductors to “be spliced or joined with a mechanical splicing device listed for this purpose”.

Below is a sample of NFPA 731. For the complete section, see the actual NFPA 731 text at NFPA.ORG. Once there, click on the free access link to the latest edition of NFPA 731.

4.6.3 Wiring.

4.6.3.1 The installation of all wiring, cable, and equipment shall be performed in accordance with NFPA 70, Article 725 or Article 800, where applicable.

4.6.3.3 A conductor shall be spliced or joined with a mechanical splicing device listed for this purpose

Below is a sample of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the latest NEC^® edition of NFPA 70.

725.3 Other Articles. Circuits and equipment shall comply with the articles or sections listed in 725.3(A) through (N). Only those sections of Article 300 referenced in this article shall apply to Class 1, Class 2, and Class 3 circuits.

300.15 Boxes, Conduit Bodies, or Fittings — Where Required. A box shall be installed at each outlet and switch point for concealed knob-and-tube wiring. Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed. Where the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, nonmetallic-sheathed cable, or other cables, a box or conduit body shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point, unless otherwise permitted in 300.15(A) through (L).