HWL-LF — System Sensor L-Series indoor low frequency sounder, wall mount, white, no marking, producing a 520 Hz ± 10% square wave tone. It replaces the earlier HW-LF.
The HWL-LF is a sounder only — it has no strobe and therefore no candela setting. It exists to satisfy the NFPA 72 requirement that audible appliances in sleeping spaces produce a low frequency 520 Hz square wave signal. The appliance uses the L-Series plug-in design with a universal mounting plate carrying an onboard shorting spring, so notification appliance circuit wiring lands on the plate and continuity can be verified before the sounder itself is installed. A rotary switch selects the tone pattern and volume; sounder-only models such as this one add a Coded position that the sounder strobes do not have.
Specifications
| Type |
Low frequency sounder, wall mount (no strobe) |
| Color / marking |
White, no marking (housing permanently marked “520 Hz”) |
| Tone frequency |
520 Hz ± 10% square wave |
| Nominal voltage |
Regulated 24 DC/FWR |
| Operating voltage range |
16 to 33 V (24 V nominal) |
| Rotary switch positions |
Temporal 3, Temporal 4, Continuous and Coded, each at High or Low volume (8 positions) |
| Sound output (reverberant) |
80 dBA at High, 76 dBA at Low |
| Current draw, High volume |
108 mA DC / 150 mA FWR at Temporal 3; 111 mA DC / 151 mA FWR at Temporal 4, Continuous and Coded |
| Current draw, Low volume |
78 mA DC / 76 mA FWR at Temporal 3; 80 mA DC / 76 mA FWR at Temporal 4, Continuous and Coded |
| Operating temperature |
32°F to 120°F (0°C to 49°C) |
| Humidity range |
10 to 93% non-condensing |
| Input terminal wire gauge |
12 to 18 AWG |
| Dimensions |
5.6" L x 4.7" W x 1.5" D (142 mm L x 119 mm W x 38 mm D) |
| Dimensions with SBBWL back box |
5.70" L x 4.8" W x 3.3" D (145 mm L x 120 mm W x 87 mm D) |
| Listing |
UL 464 |
Installation notes
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Sounder, not a sounder strobe: there is no strobe and no candela selection on this model. If the space also needs visible notification, use a P2WL-LF or add a separate strobe.
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Back boxes: mounts to a standard 4 x 4 x 1-1/2-inch back box, a 4-inch octagon box, or a double-gang box. Being a 2-wire product it may also mount to a single-gang 2 x 4 x 1-7/8-inch back box.
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Coded operation: for coded tones the temporal coding must be provided by the NAC. If NAC voltage is held constant the sounder output stays constantly on; the published coded current ratings are for continuous voltage.
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Synchronization: compatible with the MDL3 Sync•Circuit module. When used with the MDL3, 24-volt rated NAC outputs must operate between 16.5 and 33 volts — a narrower low end than the appliance’s own 16 V minimum.
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Panel compatibility: if the appliances are not UL 9th edition listed with the panel or power supply in use, consult the panel compatibility listing to determine the maximum number of devices on a circuit.
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Indoor use only: rated for indoor installation from a regulated DC or full-wave rectified unfiltered supply.
Related models
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HRL-LF — the same wall low frequency sounder in a red housing.
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HGWL-LF — compact wall low frequency sounder, white, in a smaller 5.25" x 3.46" x 1.5" housing.
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HCWL-LF — ceiling mount low frequency sounder, white, 6.8" diameter x 1.4" high.
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P2WL-LF — wall low frequency sounder strobe, white, adding field-selectable candela.
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MDL3W — Sync•Circuit synchronization module, white.
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SBBWL — white surface mount back box for wall L-Series appliances.
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.
