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Fire Alarm

Life Safety wiring is function wiring with an added life safety aspect
Power Limited wiring carries signals to and from devices. Life Safety wiring adds supervision to the wiring to make quick repairs, keeping the system working.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

Why is Supervised Wiring So Important?

By Douglas Krantz

Based on Life Safety considerations, supervision makes the difference between building low voltage wiring and building fire alarm system wiring.

Low voltage (Power Limited) Wiring Is Function Wiring

The idea with power limited wiring is to make sure that power or signals get through, and they aren't interfered with. If something goes wrong with the wiring, the wiring can be fixed the next business day, or week, or whenever it's convenient. No one is going to be hurt if the problem exists a little while.

Fire Alarm Wiring is Function Wiring --- with Added Life Safety Considerations

Fire alarm system wiring takes the concept of low voltage wiring one step further. Not only does it have to function, but because it's there for Life Safety it has to function all the time; if the wiring doesn't work, people can die.

When something goes wrong, Life Safety means that the problems have to be fixed --- now --- before anything bad happens.

Continual Electronic Supervision

For anyone to know there's a problem, when fire alarm technicians aren't on site with their meters, continual electronic supervision of the wiring is the only method that can be used. This type of supervision lets people know there's a problem (trouble), and then the problem can be fixed.

Supervision - the Idea of Life Safety Wiring

For example, if a telephone extension goes bad, especially in a room that's not used very much, that problem may have been caused by something bumping into it. The next month, the problem with the telephone might finally be noticed and then the telephone would be fixed.

The telephone isn't continually supervised.

Instead of bumping the telephone, that object may bump the smoke detector. Without continual supervision, the problem with the smoke detector wouldn't be noticed until someone went into the room and noticed it was knocked down. Being on the ceiling, it might not be noticed for years, if ever.

But if, before someone noticed the problem with the smoke detector, a fire started in the room, the smoke detector wouldn't detect the smoke. By the time the fire progressed into the next room where there was a working smoke detector, the fire would be out of control.

All this, of course, is unless using the fire alarm system's supervision the missing detector was noticed and fixed right away.

Fire Alarm Wiring Supervision

The whole idea of fire alarm system wiring is centered around life safety. The wiring is continually supervised by the fire alarm control panel (continually checked electronically for faults --- open or broken wiring, ground faults, sometimes wire to wire shorts), and when a problem occurs, the panel shows a "trouble" with the fire alarm system.

Life Safety --- Fixing the Trouble Right Away

When there's trouble with the system, the fire alarm panel shows an amber light and sounds its local buzzer; It gets people's attention. It indicates that something needs to be fixed. It annoys the building's occupants and the building owners until they call for service. The problem then gets fixed.

That's life safety supervision.

More information on Supervised Wiring and Life Safety can be found in the book "Make It Work - Conventional Fire Alarms" by Douglas Krantz.

More Articles

How Do You Troubleshoot Using Supervision Voltage? -- With Fire Alarm Systems , one method of troubleshooting is measuring supervision voltage . It's the voltage at the panel's IDC input terminals (Initiating Device Circuit for... Read More

What's the Difference Between Class A and Class B? -- The Fire Alarm System is a Life Safety System - so the occupants of a building can escape quickly, the idea behind a Fire Alarm System is that it will provide a warning that there is a fire. The trouble is, if something is wrong with the system, like a wire is broken somewhere in the building, the Fire Alarm System... Read More

Why Does the Fire Alarm Panel Supervise the Wires? -- Supervision of building wiring isn't really to make sure the wires are good, supervision of building wiring is to make sure all the devices are ... Read More

What is Fire Alarm Class B Wiring? -- Fire alarm people are paranoid. They're afraid everything is working against them. They're in fear that that if anything goes wrong... Read More

 Get your free diagram showing supervision for Class B wiring

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