2 wire sounder question

[Patrick Griffin]

In a 2 wire fire alarm system (non conventional) the sounder polarity is reversed to initiate the decive. Is L at the panel actually N in a non alarm state so? And in alarm state it reverses so current can flow through the diode initiating the decive.

 

[Patrick Griffin]

Sorry i meant in a converntional panel

 

[tazz]

On most conventional, but not all...the bell circuit polarity is reversed on alarm activation. Hence the diode on sounders and bell units. On a 2 wire conventional system, like Kentec Sigma T series or Haes Excel, the Zone is also reversed polarity on alarm activation.

 

[Patrick Griffin]

Thanks tazz.

In a non conventional 2 wire system which has as you know only one circuit for initiating devices and alarm devices, the alarm devices also swap polarity to activate i beleieve, how does this happen if everything is on the same circuit? Is the entire circuit reversed polarity including initiating devices?

 

[tazz]

All manufactures detection will work reverse polarity without a problem, but the diode bases block the path. so most manufactures request Sav bases to over come this. All sounders/bells are then wired reverse polarity, on the same zone circuit, so when activated, the polarity is reversed, and sounders active.

 

[Patrick Griffin]

Sav bases are on both initiating and alarm devices except the manual call point which should always be wired first on the circuit correct??

 

[tazz]

Sav bases are used on all detection, smokes, heat etc. They allow the circuit to be monitored for head removal, and activation. Call points are standard 470 ohm types. You can place call points anywhere on the circuit, they do not have to be wired first. Sounders are standard, wired in reverse.

 

[Patrick Griffin]

Thanks very much, im understanding it alot more now, things are a bit more detailed than the old conventional system thats for sure

 

[tazz]

Its wired basically the same, but allows you to add sounders on the same zone wiring. Unlike the now obsolete Twinflex, the sav bases offer the use of good quality detection such as Apollo S65, and hochiki. Attached is kentec sigma manual, may help to explain better.
View attachment Sigma Manual.pdf

 

[Patrick Griffin]

Thanks tazz.

I have one final question if you don't mind please, why have we a 470 ohm resistance at manual call point?

 

[Patrick Griffin]

I would guess its to differentiate between an actual fire and a short circuit (non fire event) caused by incorrect wiring, am i right?