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.

NEC Article 725 covers Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits which are often used in a security system. NEC^® Article 800 covers communications systems such as phone lines which are often used to alert security monitoring companies of a potential breach in the system.

NEC Article 100 defines each of the different circuit types covered in Article 725.

• A Class 1 circuit is the portion of the wiring system between the load side of the overcurrent device (circuit breaker or fuse) or power-limited supply such as a Class 1 transformer and the connected equipment. There are two types of Class 1 circuits:
  • Class 1 power limited circuits which are supplied from a source that has a rated output of not more than 30 volts and 1000 volt-amperes.
  • Class 1 remote-control and signaling circuits which can operate up to 600 volts.
• A Class 2 circuit is the portion of the wiring system between the load side of a listed Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit is considered safe from both fire and electric shock. Class 2 cables are required to have a voltage rating of no less than 150 volts.
• A Class 3 circuit is the portion of the wiring system between the load side of a listed Class 3 power source and the connected equipment. Because of its power limitations, a Class 3 circuit is considered safe from only a fire initiation standpoint, but not from electric shock which is why Class 3 cables are required to have a higher voltage rating (usually at least 300 volts). Since higher levels of voltage and current than for Class 2 are permitted, additional safeguards are specified in Article 725 to provide protection from an electric shock hazard that could be encountered.

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 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.

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.

Article 100 Definitions:

Class 1 Circuit. The portion of the wiring system between the load side of the overcurrent device or power-limited supply and the connected equipment.

Informational Note: See 725.41 for voltage and power limitations of Class 1 circuits.

Class 2 Circuit. The portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit is considered safe from a fire initiation standpoint and provides acceptable protection from electric shock.

Class 3 Circuit. The portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Due to its power limitations, a Class 3 circuit considers safety from a fire initiation standpoint. Since higher levels of voltage and current than for Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered.