System Sensor HWL-LF-BP10 — bulk pack of ten HWL-LF L-Series indoor low frequency sounders: standard wall-mount, white, 520 Hz ±10% square wave tone, listed to UL 464. These are sounders only — there is no strobe and no candela setting.
The L-Series low frequency line exists to satisfy the NFPA 72 sleeping space requirement for a notification appliance operating at 520 Hz ±10% with a square wave tone, which research shows wakes sleeping occupants far more reliably than a conventional 3 kHz horn, including those with mild to severe hearing loss. The HWL-LF is powered from a notification appliance circuit and operates on nominal 24 volts. A rotary switch on the device selects the tone and volume: Temporal 3, Temporal 4, Continuous or Coded, each at a High or Low volume setting — eight positions in total. Coded operation is available on sounder-only models like this one and not on the sounder strobes. A plug-in design with minimal intrusion into the back box keeps installation fast and largely eliminates ground faults, and the universal mounting plate carries an onboard shorting spring so wiring continuity can be verified before the device is fitted, protecting appliances from construction damage. The housing carries a permanent “520 Hz” marking. Buying by the ten-pack suits dormitories, hotels, assisted living and multifamily projects where the same sleeping-room appliance repeats on every floor.
Specifications
| Model |
HWL-LF, white (HRL-LF is the red equivalent) — supplied here as a 10-unit bulk pack |
| Type |
Indoor low frequency sounder, standard wall mount — no strobe |
| Frequency range |
520 Hz ±10%, square wave tone |
| Nominal voltage |
Regulated 24 VDC or FWR |
| Operating voltage range |
16 to 33 V (24 V nominal) |
| Tones |
Temporal 3, Temporal 4, Continuous, Coded — each with High and Low volume |
| Current, Temporal 3 High |
108 mA DC / 150 mA FWR — 80 dBA |
| Current, Temporal 3 Low |
78 mA DC / 76 mA FWR — 76 dBA |
| Current, Temporal 4 High |
111 mA DC / 151 mA FWR — 80 dBA |
| Current, Temporal 4 Low |
80 mA DC / 76 mA FWR — 76 dBA |
| Current, Continuous High |
111 mA DC / 151 mA FWR — 80 dBA |
| Current, Continuous Low |
80 mA DC / 76 mA FWR — 76 dBA |
| Current, Coded High |
111 mA DC / 151 mA FWR — 80 dBA |
| Current, Coded Low |
80 mA DC / 76 mA FWR — 76 dBA |
| Sound output |
80 dBA high volume, 76 dBA low volume (UL reverberant) |
| Operating temperature |
32°F to 120°F (0°C to 49°C) |
| Humidity range |
10 to 93%, non-condensing |
| Dimensions |
5.6″ L × 4.7″ W × 1.5″ D (142 × 119 × 38 mm) |
| Input terminal wire gauge |
12 to 18 AWG |
| Back boxes |
4 × 4 × 1½″, 4″ octagon, or double-gang; two-wire products also mount to a single-gang 2 × 4 × 1⅝″ box |
| Listing |
UL 464, approved for fire protective service |
Installation notes
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No strobe, no candela: the HWL-LF is a sounder. Field-selectable candela settings apply to the L-Series low frequency sounder strobes (P2WL-LF wall, PC2WL-LF ceiling), not to this device. Where the ADA visible-signaling requirement applies, a sounder alone will not satisfy it.
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24 V device: the low frequency sounder operates on nominal 24 volts over a 16–33 V range from a regulated DC or full-wave rectified supply. Do not design it onto a 12 V notification circuit.
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FWR draws substantially more current than DC: Temporal 3 High is 108 mA on regulated DC but 150 mA on FWR. Size the notification appliance circuit for the supply type actually used — a ten-device pack on FWR is roughly 1.5 A at high volume, not 1.08 A.
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Coded operation needs the NAC to do the coding: for coded tones the temporal coding must be provided by the notification appliance circuit. If NAC voltage is held constant, the sounder output stays constantly on. The published coded ratings are for continuous voltage.
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Low volume is only 4 dBA down: high is 80 dBA and low is 76 dBA reverberant, but the current saving is significant (111 mA to 80 mA on DC). Use low volume to extend circuit capacity where the audibility calculation still passes.
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Synchronization: the device is compatible with the Sync•Circuit MDL3 module, which synchronizes low frequency sounders at Temporal 3. With the MDL3, 24-volt rated NAC outputs operate between 16.5 and 33 V. The MDL3 will not operate on a coded power supply.
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Test the wiring first: the universal mounting plate has an onboard shorting spring so circuit continuity can be checked before any sounder is plugged in. Terminate the NAC wiring at the mounting plate.
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Retrofit compatibility: the L-Series is electrically compatible with legacy SpectrAlert and SpectrAlert Advance devices and is a direct replacement for HW/R-LF.
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Indoor only: rated 32°F to 120°F and 10–93% RH non-condensing. For surface mounting where no back box is recessed, use the SBBWL surface mount back box.
Related models and accessories
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HRL-LF — same standard wall low frequency sounder in red
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HGWL-LF — compact wall low frequency sounder, white; 5.25″ L × 3.46″ W × 1.5″ D
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HCWL-LF — ceiling low frequency sounder, white; 6.8″ diameter × 1.4″ high
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P2WL-LF — wall low frequency sounder strobe with field-selectable 15, 30, 75, 95, 110, 135 and 185 cd settings, listed to UL 1971 and UL 464
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PC2WL-LF — ceiling low frequency sounder strobe, 15, 30, 75, 95, 115, 150 and 177 cd
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MDL3W — Sync•Circuit module, white, UL listed
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SBBWL — surface mount back box for the standard wall sounder; SBBGWL for the compact wall sounder; SBBCWL for the ceiling sounder
Specifications taken from the System Sensor data sheet “Indoor Selectable-Output Low Frequency Sounders and Low Frequency Sounder Strobes,” document AVDS910-02 (11/02/2020). Manufacturer specifications are subject to change without notice.
