Because of the potential fire and explosion hazards caused by the improper handling and installation of electrical wiring. certain rules in the selection of materials and quality of workmanship must be followed as well as precautions for safety,. The National Electrical Code® (NEC® ) was developed to standardize and simplify these rules and provide some reliable guide for electrical construction.
The NEC® is published (and frequently revised) by the National Fire Protection Association (NFPA), Batterymarch Park. Quincy, MA 02269. It contains specific rules and regulations intended to help in the practical safeguarding of persons and property from hazards arising from the use of electricity,, including low voltage. used in the majority of security/fire-alarm systems.
Article 725 of the NEC® covers remote-control. signaling, and power-limited circuits that are not an integral part of a device or appliance. The NEC® (section 725-1) states:
The circuits described herein (Article 725) are characterized by usage and electrical power limitations that differentiate them from light and power circuits and. therefore. special consideration is given with regard to minimum wire sizes, derating factors, overcurrent protection, and conductor insulation requirements.
Personnel assigned to install security/fire-alarm systems should become familiar with Article 725 of the NEC® as well as Article 760, "Fire Protective Signaling Systems." This article covers the installation of wiring and equipment of fire- protective signaling systems operating at 600 volts or less.
Other NEC ® articles of interest to security/fire- alarm installers include the following:
1. Section 300-21, 'Spread of Fire or Products of Combustion."
2. Articles 500 through 516 and Article 517, Part G (dealing with installations in hazardous locations).
3. Article 110, "Requirements for Electrical Installations" and Article 300. "Wiring Methods."
4. Article 310. - "Conductors for General Wiring."
5. Fire-protectile signaling circuits and equipment will be grounded according to Article 250, except for dc-power limited fire-protective signaling circuits that have a maximum current of 0.03 amperes.
6. The power supply of nonpower-limited fire- protective signaling circuits will comply with chapters 1 through 4 and the output voltage will not be more than 600 volts, nominal.
7. Conductors of No. 18 and No. 16 sizes will be permitted to be used provided they, supply loads that do not exceed the ampacities given in table 402-5 and are installed in a raceway or a cable approved for the purpose. Conductors larger than No. 16 will not supply loads greater than the ampacities given in tables 310-16 through 310-19.
8. When only nonpower-limited fire-protective signaling circuits and Class 1 circuits are in a raceway, the number of conductors will be determined according to section 300-17. The derating factors given in Note 9 to tables 310-16 through 310-19 will apply if such conductors carry continuous loads.
9. Where power-supply conductors and fire- protective signaling circuit conductors are permitted in a raceway according to section 760-15, the number of conductors will be determined according to section 300-17. The derating factors given in Note 8 to tables 310-16 through 310-19 will apply as follows:
a. For all conductors when the fire- protective signaling circuit conductors carry continuous loads and the total number of conductors is more than three.
b. For the power-supply conductors only when the fire-protective signaling circuit conductors do not carry continuous loads and the number of power-supply conductors is more than three.
10. When fire-protective signaling circuit conductors are installed in cable trays. comply with sections 318-8 through 318-10.
The installation of a protective security/fire-alarm circuit should always start at the protective-circuit energy source, as if it were an end-of-line battery-a battery. remote from the control panel-even though it may actually be a power supply installed in the panel. A pair of wires is run from this power source to the first contact location, but just the positive wire is cut andContinue Reading