Ebe 235 Electrical Power Utilization

...

Class-A Fire Alarm Circuit:

The Class-A circuit utilizes a pair of wires to attach to all of the devices and then a pair returns back to the panel. NFPA 72 requires that a minimum distance separates the outgoing and return wires on class-A wiring. If a break occurs anywhere in the circuit, every device is still active due to the redundant circuit paths. There are four wires, two supplying power to the front of the circuit and two supplying power from the end of the circuit. [pic 2][pic 3]

Figure: Class-A Fire Alarm Circuit connection

Fire alarm systems that are wired in Class A return the wires via a different path to the control panel. Class A wired fire alarm systems include line isolators that automatically isolate any short in the wiring, while the rest of the loop functions without disruption. The control panel will notify of this condition so that maintenance personnel can rectify the problem.

Class A fire alarm system are slightly more costly than Class B wiring, due to the extra hardware and wiring required, however the redundancy and peace-of-mind they provide easily justify the additional cost. Class A is suitable FOR almost all fire alarm systems – all that is required is proper wiring.

Class-B Fire Alarm Circuit:

Class B is the more common of the two fire alarm systems, and it is the error in its design that led to Class A systems being designed. When a Class B system sounds, if there is any sort of short in the wiring system, then all of the peripheral systems are effectively lost. The alarm can communicate with the security office, but if there's a short from the alarm to the sprinkler, the connection from the sprinkler to a further device such as a red light, all of the other devices are unable to be accessed.[pic 4][pic 5]

Figure: Class-B Fire Alarm Circuit connection

In conventional Class B Loops, all devices are daisy-chained together. By watching a small electrical current passing through the wires, the panel supervises them, and to limit this supervising current, at the end of the daisy-chain is an end-of-line resistor. The panel constantly watches for this current.

If the supervising current stops flowing, the panel assumes a wire is broken (an open fault), and displays a trouble. When a wire breaks in Class B, the devices closest to the panel will still work, but because of the wire break, the devices further from the panel are cut off.

Answer to the Question No. 06

To understand the difference between an addressable fire alarm system and an analog we must first understand what a fire alarm system is. In general a fire alarm system is a group of visual and audio devices (automatic and/or manual)-i.e. smoke detectors, heat sensors, strobes, alarm pulls, and sprinklers-linked to a main fire panel that sends a signal to local emergency responders when an alarm is activated. Each device has to be linked to the main fire panel, but there are different methods of doing so. This is where the big difference between addressable and conventional comes into play.

Addressable fire alarms system:

Addressable fire alarms indicates that each installed device or module is connected to the main fire panel in a “loop” often by means of a singular wire. Conventional alarm systems require individual wires per each device, again connecting back to the main fire panel. The most obvious difference between the two, in terms of installation, is cabling requirements and labor costs. Due to the fact that addressable systems require less cabling they make for less complex installations. That’s not to say there aren’t situations where a conventional system might make more sense. Although it seems most new construction projects implement addressable systems.

One of the many benefits of an addressable fire alarm system is that each device is given its own unique address. In the event of a triggered alarm a single device can be pinpointed which gives responders a more concise location as to where a fire might be occurring. This helps save precious time and improves life safety. It’s also helpful in the event a device is malfunctioning or requires maintenance. According to Jim Kimpel, product manager for Fire Control Instruments, Inc., being able to pinpoint specific devices lessens the hesitation an end-user might have-mostly caused by the fear of costs-when making a service call. This helps prevent unnecessary losses due to a defunct system. [pic 6][pic 7]

Figure: Addressable Fire Alarm System

As with any alarm system, routine inspections are required for addressable fire alarm systems. According to Brandt Phillips, Commercial Fire & Security Director of Sales for Napco Security Technologies Inc., inspections and system testing are made easier with addressable systems. He says installing an addressable system, “…eliminates the need for expensive testers, excessive labor for testing, and gives you the ability to automatically generate the same reports directly from the software you used to program the panel…” In comparison Phillips points out that inspections for conventional systems can cost thousands and be quite lengthy.

Analog fire alarms system:

0While conventional systems may require extensive wiring, intensive testing, a higher labor cost, and are being phased out by addressable alarms, they’re not completely disregarded when it comes to installations. The size of a project may deter mine what type of system is a better fit. [pic 8][pic 9]

Figure: Analog Fire Al arm Systems

It seems that for small jobs, i.e. a single story office building, conventional systems may work just fine. They’re initial upfront costs are fairly low and if you’re not dealing with multiple floors and zones it may not be necessary to implement an addressable system. However, the appeal of quick installs, concise reporting of fire occurrences, and the ease of inspection and system testing will continue to draw support for addressable systems; it seems to be the trend in most new construction projects. We can discuss the differences in a table form that is as follows:

Parameters

Analog

Addressable

Building Size

Appropriate for small buildings such as retail store