NAC Current Draw Chart

Typical current draw for a 2-wire horn/strobe notification appliance by candela rating at 24 V — planning values to size a circuit and battery before the data sheets are in hand. Values are manufacturer-typical (System Sensor SpectrAlert Advance, UL-max DC); the final numbers come off the actual device data sheets.

Typical horn/strobe current by candela

Manufacturer typical
UL-max current at 24 V DC input for a typical 2-wire horn/strobe (System Sensor SpectrAlert Advance). Manufacturer-typical planning values — verify against the specific device data sheet.
CandelaTypical current (mA)Amps
15 cd91 mA0.091
30 cd116 mA0.116
75 cd176 mA0.176
95 cd201 mA0.201
110 cd221 mA0.221
Higher-candela appliances (135–185 cd) and higher horn volumes draw more, and full-wave-rectified panel outputs draw slightly more than filtered DC. A single 15 cd device can draw as little as ~66 mA on a low-volume temporal setting — always use the data-sheet value for the tone and volume you field-configure.

What this feeds

Appliance current is the input to two other calculations. Total the current on a circuit and it drives the NAC voltage drop and wire size — more current means more drop and a shorter maximum run. Total the alarm current across the whole system and it feeds the alarm term of the standby battery calculation. Because these values set both the wire and the battery, use the worst-case UL-max figures, not the nominal or low-volume numbers.

Common questions

How much current does a horn/strobe draw?

It depends on the candela and the specific device, but for a typical 2-wire horn/strobe at 24 V the draw rises from about 91 mA at 15 cd to about 221 mA at 110 cd. Higher candela and higher horn volume draw more, and a full-wave-rectified panel output draws slightly more than filtered DC. These are worst-case (UL-max) values — the right ones for sizing circuits and batteries.

Are these current values exact?

No — they are manufacturer-typical (System Sensor SpectrAlert Advance, UL-max DC) and shown for early planning. Actual draw varies by manufacturer, model, horn tone and volume setting, and DC-versus-FWR input. Always total the circuit from the actual device data sheets before finalizing a voltage-drop or battery calculation.

Why size to the UL-max current?

The UL-max column is the worst-case current the appliance can draw within its listed voltage range. Sizing wire and batteries to it guarantees the circuit works even at the low end of the regulated voltage window, where devices draw the most current to hold their output.

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