Fire alarms wiring

The cable has a small overall diameter when compared to alternative cables and may be supplied as bare copper or with a PVC oversheath. It is colour-coded orange for general electrical wiring, white for emergency lighting or red for fire alarm wiring. The copper outer sheath provides the CPC, and the cable is terminated with a pot and sealed with compound and a compression gland (see Fig. 3.40). 

In the event of fire within a building, the controller for each elevator should isolate all manually operated inputs and return automatically to the evacuation level, usually the ground floor. An output from the building fire alarm panel is hard wired to the elevator controller, giving the signal for a fire condition. The elevator remains disabled at the evacuation level and the car doors open. If a fire officer requires control of a elevator a key switch or break-glass unit should be used to re-activate the elevator. 

Wires and cables used for fire-alarm systems and smoke alarms must comply with the above and one of the following ... 

Install critical power, control, instrument, and alarm wiring and pneumatic tubing outside the fire-exposed envelope. Cable trays and conduit banks should be routed underground or on the upper levels of elevated pipe racks at least 30 feet above the ground and outside the drainage path of hydrocarbon spills. Install fire proofing of critical systems and equipment if they are inside the fire-exposed envelope. 

Elementary and Wiring Diagrams, Fire Alarm System, Hot Cell Details and Equipment and Conduit Schedule, Fire Alarm System, Hot Cell... 

Fire alarm circuits are wired as either normally open or normally closed. In a normally open circuit the alarm call points are connected in parallel with each other so that when any alarm point is initiated the circuit is completed and the sounder gives a warning of fire. In a normally closed circuit the alarm call points are connected in series to normally closed contacts. When the alarm is initiated, or if a break occurs in the wiring, the alarm is activated. 

The wiring of a fire alarm system is as important as the detectors themselves. It should be protected from mechanical and fire damage and have an electrical supply which is either independent of the normal supply to the premises or is backed up by an independent supply. The control and indicator board apart from showing which detector has operated, should also show power supply faults, wiring faults and any other faults which may affect the security of the system. 

Ceramizable (ceramifiable) silicone rubber-based composites are fire resistant materials developed especially for cable covers application. In case of fire, electrical installations are endangered of short circuit effect which can deactivate lots of important devices, like fire sprinklers, elevators, fire alarms or lamps indicating route to emergency exits. Ceramizable composites are able to sustain functioning of electric circuit on fire and high temperature up to 120 min by producing ceramic, porous layer protecting copper wire inside a cable. 

Figure 15.11 A temporary, wired-in fire alarm during major renovation of a large and complex multi-storey building.

If it is thought that there might be some deiay in fire being detected, automatic fire detection should be considered, linked into an electrical fire alarm system. Where a workplace provides sleeping accommodation or where fires may develop undetected, automatic detection must be provided. If a workplace provides sleeping accommodation for fewer than six people, interlinked domestic smoke alarms (wired to the mains electricity supply) can be used provided that they are audible throughout the workplace while people are present. 

If the occupants of a building have impaired hearing it may be appropriate to provide visual alarm systems in the areas occupied by those people. This should include any toilets and welfare facilities. If people with impaired hearing sleep in the building it may be appropriate to provide tactile devices linked to visual alarm devices. These devices may, for example, be placed under pillows and wired into the fire alarm circuits or be triggered by radio signals. 

The fire alarm system not being switched off while its wiring is being altered... 

Fire alarm circuits are wired as either normaiiy open or normally closed. 

The colors purple, brown, black, and gray have not been assigned a safety connotation. Specific color codes are also employed in the identification of alarms panel indicators, piping, compressed gas cylinders, electrical wiring, fire sprinkler temperature ratings, etc. Although these sometimes do not correspond with similar meanings. 

Travelling at great speed, the cloud — a mixture of chlorine and phosgene — outstripped the alarm system of gongs and klaxons and took hundreds of men unawares one man was gassed five miles behind the front line. Panic set in on the dark winter morning as shell fire cut all the telephone wires to the front. It was mid-afternoon... 

The Health Care Facilities Standard, NFPA 99, created criteria to minimize the hazards of fire, explosion, and electricity in health care facilities. It specifically addresses electrical system wiring, storage, and use of flammable and combustible liquids in laboratories, emergency and disaster management, oxygen storage, alarms, and design considerations (NFPA, 2002). 

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