LOW FREQUENCY HORNS AND NEW NFPA CODE
LOW FREQUENCY HORNS – NEW CODE – Sheet attached with specific code reference and information. This code went into effect 1 January 2014 – It came out in the 2010 code and is also found in the 2013 code as well.
New NFPA 72 code requires special LOW FREQUENCY HORNS in hotel, motel, retirement, apartments and condominium type construction. These new low frequency appliances will wake people up more effectively. They do have a higher mA draw than the old mini horns you were used to so plan the circuits accordingly. One example is the System Sensor HR-LF which is the horn only (red) and the Horn/Strobe version is P2RH-LF (Red) these should be used in the ADA rooms using the high candela (cd) 177 setting much of the time.
76 db (Sound level) on Temporal 3 setting at 520 Hz
Low Frequency Horn draws 138mA each (16-33volts) Low Frequency Horn/Strobe at 177 cd (candela) draws 343mA
For just the Horns on a 2 amp circuit you could install 14 of them and be ok but the engineers only want us to use 75% of the circuit or 1500 mA so we should limit the LF HORNS to 10 per 2amp circuit.
Using the LF Horn/Strobes you could only put four (4) per circuit on a 2amp circuit if you want to save 25% for spare.
USING A NORMAL 75cd HORN/STROBE that draws 242mA you can put only 6 on a circuit (System Sensor example of the adjustable set at 75cd and high temporal 3 setting) Some Engineers have been using a figure of 120 mA or 130mA which is not the horn and the strobe combined unless you are using 15cd which ends up being 150mA each.
VERY IMPORTANT: IF THE PROJECT IS CLASS A WIREING YOUR 4 CIRCUIT POWER SUPPLY BECOMES ONLY A TWO CIRCUIT POWER SUPPLY
Most fire alarm manufactures use GENTEX, COOPER WHEELOCK, SYSTEM SENSOR, EDWARDS, POTTER (Sprinkler), TYCO or FEDERAL SIGNAL . (explosion proof or specialty appliances)
Keep in mind that you still need to do the battery calculations and voltage line drop calculations to make sure there is enough current at the last appliance depending on the wire gauge so the chart is an example of one of the factors you need to consider which is the mA draw of the appliance and other factors are your power supplies, wire gauge and distance etc….
Appliances per circuit based on 1.5amps of 2amp circuit Candela mA draw 10 per circuit 15cd 150 mA 8.4 30cd 178 6 75cd 242 5 110cd 286 3.93 or 4 177cd 381 Appliances per circuit based on 2.25amps of 3amp circuit 15 15cd 150 12 30cd 178 9 75cd 242 7.8 110cd 286 5.9 177cd 381 Based on System Sensor appliances P2R 15cd 30cd TEN of the 75cd units is 2.42amps HORN ONLY 84mA HORN ONLY 84mA Eight of the 75cd units is 1.93amps STROBE 66mA STROBE 94mA Six of the 75cd units is 1.452amps HORN/STROBE 150mA HORN/STROBE 178mA
If the circuit is a 2.0amp circuit only 1500mA or 1.5amps is usable leaving 25% extra 75cd 110cd HORN ONLY 84mA HORN ONLY 84mA STROBE 158mA (75cd) STROBE 202mA HORN/STROBE 242mA HORN/STROBE 286mA
177cd 95cd HORN ONLY 84mA HORN ONLY 84mA STROBE 297mA STROBE 181mA HORN/STROBE 381mA HORN/STROBE 265mA