NFPA 731, Section 5.1.4 is all about proper monitoring the integrity of security system conductors to ensure functionality and survival of important circuits. Annex A, Section A.5.1.4.2 in the back of NFPA 731 states that “one method of monitoring for integrity of initiating circuits is to utilize supervision devices located at the end of the circuit”.

It is always a good practice to ensure that security system initiating devices such as door contacts, are configured with end of line (EOL) resistors for 4-state supervisory circuits. This involves wiring a resistor in series and another resistor in parallel with the switch, at the termination point of the device. This ensures circuit supervision from the security annunciator panel, or card reader panel all the way to the actual device termination. This installation method will result in indication if the device or circuit is in one of the following four states of condition:

(1) A normal state

(2) An alarm state

(3) A shorted state

(4) A cut state

This creates a 4-state supervised installation since it distinguishes between 4 different scenarios for the device or circuit being supervised.

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.

5.1.4 Monitoring Integrity of Conductors.

5.1.4.1 All means of connection between a control unit and its primary and secondary power supplies, including accessories essential to the operation of the premises security system control unit, shall be monitored for integrity.

5.1.4.1.1 The occurrence of a single fault shall be indicated within 200 seconds.

5.1.2.1.2 The restoration to normal operation shall be automatically indicated within 200 seconds.

5.1.4.2 Wiring to all initiating devices of an intrusion detection system shall be monitored for integrity so that the presence of an off-normal condition is automatically indicated to the user upon arming of the system.

5.1.4.3 Interconnecting wiring between the protected premises control unit and the separate signal transmission equipment shall be monitored for integrity or physically protected.

5.1.4.4 A fault on wiring to initiating devices shall not restore or clear an unacknowledged alarm signal at the control unit.