Question:
- I am a Junior at Chaparral High School, in Temecula, CA, I've always enjoyed taking things apart and putting them back together, and fire alarms have been one of the things I've always wanted to explore but were always too expensive/hard to find/etc. I finally got a 12v horn/strobe from Jim Rojas through eBay, and added this to my home brew FACP (Who else do you know who has a clubhouse a little bigger than your average storage shed with its own burglar alarm (FBII XL-31), fire alarm system with voice evac and strobe?)

I have a few questions, mostly related to fire alarms, and since the fire alarm the internet groups seem to be dead except for the occasional spammer, I thought I'd post them here. If you would prefer to respond to e-mail please send it to lincoln _at_ pe _dot_ net, although the address in this message is valid, so you could simply reply.

1. I know most "standard" commercial (for lack of a better term) annunciators are 24 VDC, Why 24 and not 12, which appears to be more normal for low voltage electronics (Burglar alarms, cars, bits of computers, low-voltage lighting, etc…). Do most commercial "initiating devices" (smokes, mainly) run at 24 volts or …?

2. I've noted that many manufacturers also list 115VAC horns, why?

3. What the heck is "Analog Addressable"? How does it differ from simply "Addressable"? I've come across both while reading local ordinances as relating to life safety, as well as manufacturer's specs

4. What are the glass/plastic "break" rods for in (especially older) manual pull stations? Can a pull function without them?

5. I've noticed at my school, which has a Notifier fire system that was installed when the school opened (~4 years ago) in the Fire Alarm Terminal Cabinets in the electrical rooms there are beigeish panels mounted on what appears to be a two-gang or 4x4 electrical box with a single clear LED that flashes red approximately every ten seconds. When I was at Cal State Long Beach recently, I noticed the same panels attached to the door hold-opens for the stairwells in one of the buildings. What purpose do these serve?

I'd like to get something a little more professional than my home brew FACP, but - how should I say this - there is no way in heck I can afford even a low-end used panel based on what I've seen on Mr. Bass's site and eBay (A lot of cool stuff but either way outdated (1950s) or way too expensive (Lowest panel I've seen is $250.00)). Which leads to- a. Does anyone have a relatively modern FACP they don't want/need and would be willing to pass on to a high school student fairly , or b. The more likely solution is find a FBII XL-2P, XL-2PBV, XL-2T, XL-2TINT, or XL-20, program every zone as a fire zone, set one trigger as "Fire Bell On" (To drive the strobe and voice evac), and connect the other trigger, programmed as a fire trouble via a relay to a zone on the XL-31. I don't have enough zones on the XL-31 to deal with fire the way I want, and I'm rapidly outgrowing my somewhat unreliable home brew FACP. The reason I want to stay with FBII if I buy something is I already have a spare keypad I can connect to the system. Anyone see any reason why this wouldn't work/a better way to do it? How'bout any extra XL-2P/T panels you want to get rid of?

Sorry… This got way longer than I anticipated, but I've had these questions for a long time, and if you don't ask, you'll never know.

Answer: You have many good questions and seem to be very curious about the fire alarm circuits. I am a little rusty at this but let me see if I can help you a bit...

You need to learn the relationship of a formula called OHM's LAW. It is Voltage is the product of Current times Resistance. E=IR. As you can see 24 VDC would be more forgiving than 12 VDC if you have to run a long run of wire and have to consider the resistance and voltage drop of the wire. Notice that with a high voltage source as the voltage goes up and resistance (wire) goes up from longer runs you have not lost in current.

The 115 AC horn would be used from a local AC source thus not loading down the alarm circuits. The 115 VA. device is typically a supervision device like on a water flow alarm and allow for a local loud alarm bell to sound if something is wrong with the sprinkler system. Most fire alarm systems now us low current 24 VDC sounders.

The glass rods are to provide a clear physical indication that the device has been activated. This allows you to have many devices on one circuit and know which one was pulled as a very low cost.

Door holders are designed to automatically close doors that are in fire walls and other critical openings so that a fire will not spread as easily and will help protect people from the fire. Similar alarm circuits will unlock doors that are locked by access control. You must always remember that alarm systems are designed to protect people first and property second. Many of the doors that are held open are fire rated doors.

Write a good letter to the fire manufacturers. Tell them that it is a school project and you will be promoting there project in a local science projects. You will find a manufacturer that is willing to find some publicity and making a faithful young fine engineer out of you. You may have to ask a few, but you will find one that will send you an old model unit to use. Either that or find an old building that is being razed, you may be able to get the old system form the building before it is knocked down. Check with the local AHJ (fire chief).

I am sure you will have get some additional comments from the others in this group and I will be corrected on anything I missed here. Good luck with your future in Fire Systems.