A couple questions

Fire Alarm Help
1

Hello. I am some what new to alarms. i understand how the work( for the most part). my questions are:

  1. if i have a silent knight panel, will i different addressable device work(e.x. a Notifire detector with a silent knight panel)?
  2. how does an slc work?

Note: i am still new, so please be nice.

Thanks again,
Brandon

2
  1. Nope, devices must be of the same brand and/or protocol as the panel. There are certain exceptions, but it’s best to just use the devices that are listed as compatible.
  2. An SLC is a two-wire loop that transmits data between the panel and addressable devices. A device is “polled” when the panel checks its status and the device reports back. The LED’s on System Sensor devices flash each time they are polled. The SLC can be shared by any compatible devices such as pull stations, detectors, modules, and transponders.
3

Thanks allot! One other question i have is, are NACs supervised(from what i know they are), and if they are how? i know that the gentex commander 3 manual says it is slide mounted for easy supervision testing. But if you have several appliances on a circuit, how can it tell if one goes missing?
Thanks again,
Brandon

4

Yes, NAC’s are supervised. An end-of-line resistor is placed at the end of the circuit so that if the circuit is broken, the panel detects the loss of resistance and shows a trouble. The panel doesn’t know where the circuit was broken.

Modern NA’s like the Commander 3 have the terminals on a separate base and will break the circuit if the horn/strobe unit is removed.

5

Thanks!!! Now I can start working on a panel. First conventional, than adressable.

6

NAC supervisory is very simple – it uses an industry (and code) standard called reverse-polarity, where the NACs have 24V constantly on them but the polarity is backwards. Are you familiar with when people say “diode polarized” referring to a fire alarm signal? That’s why they do it. The polarity is backwards constantly for the supervision and when the panel goes into alarm the polarity inverts so the signals can sound.

7

Ok that helps! But does it send a full 24v before a alarm?

8

Yes, there’s 24VDC coming out the NAC circuit even if there’s no alarm. Required for supervision.

9

Ok thanks.

10

Not sure what you mean by a full 24V, I assume you mean +24V not -24V. If you meter out a NAC when not in alarm, it should be reading either a lower voltage or in the neighborhood of -24V.

11

Thanks! I’m designing a panel lol

12

Here’s what helped me.

The positive and negative terminals switch when it goes into alarm. Neg goes to pos and pos goes to neg when it’s normal. The alarms don’t sound because of the diodes. You should check https://www.youtube.com/watch?v=N6MpF8mTxtA this out, it helped me a lot while designing the 2400.