Fire alarm wiring shall be in conduit when located exposed, such as in mechanical rooms or rooms without ceiling as well as above hard ceilings. Flexible metal conduit may be used where it is infeasible to install hard conduit.
According to the National Fire Protection Association (NFPA) regulations and National Electric Code (NEC) articles, any wiring that exists in non-accessible areas or below seven feet must be installed in metallic conduit.
Article 760 (Fire Alarm Systems) of NFPA 70 (National Electrical Code) governs fire alarm system wiring and equipment, including all circuits controlled and powered by the fire alarm.
Fire alarm cables can be exposed if they are protected from physical damage. NEC Article 760 allows exposed cables above 7 feet; below 7 feet, cables should be in a raceway. Cables must be supported by the building structure to prevent damage.
760.24 Mechanical Execution of Work. (A) General. Fire alarm circuits shall be installed in a neat workmanlike manner. Cables and conductors installed exposed on the surface of ceilings and sidewalls shall be supported by the building structure in such a manner that the cable will not be damaged by normal building use.
NFPA and NEC 90 articles state that when installing a fire alarm system, any fire alarm wiring below 7 feet or in non-accessible areas must be installed in a metallic raceway, including behind drywall walls or hard ceiling surfaces.
PLFA circuits
The branch-circuit overcurrent protection device must be identified in red, accessible only to qualified personnel, and identified as FIRE ALARM CIRCUIT. The red identification must not damage the overcurrent protective device or obscure any manufacturer's markings.
For the most part, fire alarm installers do not have to run wire outdoors; however, occasionally, overhead or underground wiring will end up being something you will have to learn.
If fire alarm cabling does not have other wires or cabling nearby or other sources of electrical interference, you may not need shielding. But in facilities near heavy electrical or mechanical equipment, the interference from these devices might mean you should use shielding to protect the fire alarm cable.
Exposed wires increase the risk of electrical fire because the hot and ground wires can touch, leading to a spark that could ignite a fire. Also, there's the likelihood of electric shocks or, worse, death through electrocution.
FPLR shielded fire alarm cable is a type of cable that is specifically designed for fire alarm systems. It features two insulated copper conductors and a layer of aluminum foil shielding, which protects the signal from electromagnetic interference (EMI) and radio frequency interference (RFI).
Wall-mounted alarms should be installed not more than 12 inches away from the ceiling (to the top of the alarm). If you have ceilings that are pitched, install the alarm within 3 feet of the peak but not within the apex of the peak (four inches down from the peak).
Conduit is a necessary part of many electrical raceways, but in some cases, you might be better off with braided sleeves. Braided sleeves offer another type of protection and can help with cable organization.
NEC Article 760 specifies the wiring methods and special cables required for fire protective signaling systems. Fire alarm circuits required to comply with Article 760. Only those sections of Article 300 referenced in this article shall apply to fire alarm systems.
In addition to this, it is important to note that emergency power systems must be completely separated from your standard power supply. This means that separate conduit runs, panels, transfer stations and other necessary components must be used in conjunction with your emergency power system.
Stranded fire alarm cables are a type of cable that is made up of multiple strands of wire, which are twisted together to form a single cable. This type of cable is more flexible and easier to install than solid core cables, making it ideal for use in fire alarm systems.
A fire rated cable will be run from the panel connecting live, neutral and earth to detector live, neutral and earth. This process will continue till the last detector of that circuit and an end of line resistor or capacitor will be used to close the circuit.
There are two types of fire resistant cables: “standard” and “enhanced”, with “standard” being the most common type. “Standard” fire resistant cables are required to meet a minimum 30-minute duration of survival when tested to BS EN 50200 (PH 30), for fire alarm circuits.
In systems with a lot of cable lines and electronic equipment, the shielded cable will offer you a better signal with no interference. A shielded fire alarm cable may be required in instances of high EMI noise exposure or to avoid cross-talk between wires within the cable.
Where cables are installed within 7 feet of the floor, said cables shall be fastened in an approved manner at intervals of not more than 18 inches. Power-limited fire alarm cables are NOT permitted to be strapped to the exterior of any raceway as a means of support.
Power-limited fire alarm cables are not permitted to be placed in cable trays with electric light, power, Class 1, non-power limited fire alarm, and medium-power network-powered broadband communication circuits unless they are separated by a barrier.
Splices and terminations of power-limited fire alarm circuits must be made in listed fittings, boxes, enclosures, fire alarm devices, or utilization equipment. Wiring methods. You can use NPLFA wiring methods and materials [760.52(A)], if you choose, instead of PLFA.
Fire alarm system wiring in conduit shall be a minimum of 3/4” EMT unless noted to be larger. All device junction boxes shall be minimum 2-1/8” deep 4” square boxes with extension ring, if required.
If you buy an AC-powered smoke detector today, it will have three wires -- black, white and red. Black accepts 120 volts AC, white is neutral, and red is the intercommunication wire.