Fire alarm NAC device wiring

slc410

Member
Does it matter which pair of conductors lands on either set of contacts on NAC devices? For instance, is the two pair cable coming from the control panel to the first horn/strobe supposed to land on a specific set of contacts?
 

ryant35

Member
Location
Cypress, CA
Does it matter which pair of conductors lands on either set of contacts on NAC devices? For instance, is the two pair cable coming from the control panel to the first horn/strobe supposed to land on a specific set of contacts?
Yes, positive to positive and negative to negative. If you reverse them the strobes will activate on the supervision voltage, notification circuits are reverse polarity for supervision. Meter the terminals on the panel and they will now -12 or -24 then positive when the circuit goes into alarm.
 

luckylerado

Senior Member
Does it matter which pair of conductors lands on either set of contacts on NAC devices? For instance, is the two pair cable coming from the control panel to the first horn/strobe supposed to land on a specific set of contacts?
Other than the polarity as stated below, the device does not care which cable lands on which terminal in terms of "in and out" Generally both positives will land under one terminal and the negatives will each have their own (or vice versa, its been a while) but again those are indifferent as to which cable they are from.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Yes, positive to positive and negative to negative. If you reverse them the strobes will activate on the supervision voltage, notification circuits are reverse polarity for supervision. Meter the terminals on the panel and they will now -12 or -24 then positive when the circuit goes into alarm.
They may activate on supervision voltage, depending on the voltage level. For 24 volt systems, the usual supervision voltage is in the 13-15 volt range and most 24 volt listed devices won't work properly below 16 volts, although you might get output for 12/24 listed devices. There is the diode bias to overcome, and supervision current is very low. In that case, some of the devices will start to "whine"; a very low audible output but usually no strobe output.
 

ryant35

Member
Location
Cypress, CA
They may activate on supervision voltage, depending on the voltage level. For 24 volt systems, the usual supervision voltage is in the 13-15 volt range and most 24 volt listed devices won't work properly below 16 volts, although you might get output for 12/24 listed devices. There is the diode bias to overcome, and supervision current is very low. In that case, some of the devices will start to "whine"; a very low audible output but usually no strobe output.
In my experience the supervision voltage on the panels I've worked is 24.
 
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