| Device Type | Qty | Standby (mA) | Alarm (mA) | Circuit | Notes |
|---|---|---|---|---|---|
| Horn | 10 | 0 | 50 | A | Single tone appliances |
| Strobe | 8 | 0 | 120 | A | 15/75 cd equivalent |
| Horn/Strobe | 6 | 0 | 170 | B | Combined units |
| Speaker | 12 | 0 | 90 | B | 25V speaker example draw |
- Device Standby (A) = Qty × Standby(mA) ÷ 1000
- Device Alarm (A) = Qty × Alarm(mA) ÷ 1000
- Circuit Total = sum of all devices assigned to that circuit
- Loop Resistance (Ω) = R(Ω/1000ft) × (2 × Length(ft)) ÷ 1000
- Voltage Drop (V) = Alarm Current (A) × Loop Resistance (Ω)
- End Voltage (V) = Supply Voltage − Voltage Drop
- Battery Ah = ((Istandby×Hours)+(Ialarm×(Minutes/60))) ÷ Derating
- Supply Required (A) = Ialarm × (1 + Margin%/100)
- Enter your supply voltage, sizing margin, and standby/alarm durations.
- Set each circuit’s one-way length and wire gauge used onsite.
- Add device lines with quantity and standby/alarm current in mA.
- Assign each device to a circuit and confirm current from datasheets.
- Click Calculate to view totals, voltage drop, and sizing guidance.
- Use Download CSV or Download PDF to document your results.
Load summary for notification circuits
Notification load is the current drawn by audible and visible appliances on each circuit. This calculator totals standby and alarm currents from device lines, then rolls them up per circuit and for the whole system. The alarm total is commonly used to check circuit rating, size the power supply, and verify battery capacity for the required standby and alarm duration.
Power supply sizing with margin
Supply sizing is based on alarm current with an added safety margin. Many projects apply a 10–30% margin to cover tolerances, future additions, and real-world conditions. Use your project’s acceptance criteria and always confirm manufacturer limits for the control unit and expansion supplies.
Battery capacity planning
Battery amp-hours are computed from standby current multiplied by standby hours plus alarm current multiplied by alarm hours. A derating factor is then applied to account for aging, temperature, and discharge characteristics. If your jurisdiction or specification requires 24 hours standby and 5–15 minutes alarm, set those values directly in the inputs.
Voltage drop and circuit performance
Voltage drop is estimated using loop resistance and total alarm current on the circuit. Longer runs and smaller conductors increase resistance, which reduces end-of-line voltage. If the calculated end voltage drops below the minimum device voltage, the circuit is flagged as CHECK so you can reduce load, shorten runs, or increase conductor size.
Example data for quick verification
Example: Circuit A length 250 ft, AWG 18, supply 24 V. Devices: 10 horns at 50 mA and 8 strobes at 120 mA. Alarm current = (10×50 + 8×120) / 1000 = 1.46 A. With AWG 18 loop resistance ≈ 6.385×(2×250)/1000 = 3.19 Ω, voltage drop ≈ 1.46×3.19 = 4.66 V, end voltage ≈ 19.34 V.
| Item | Value | Notes |
|---|---|---|
| Circuit | A | Example circuit |
| Length | 250 ft | One-way run |
| Wire | AWG 18 | Copper |
| Alarm Current | 1.46 A | Horns + strobes |
| Voltage Drop | 4.66 V | Estimated at alarm |
| End Voltage | 19.34 V | Compared to minimum |
1) What is “notification load” in practical terms?
It is the electrical current drawn by horns, strobes, speakers, and related appliances. Summing device currents shows whether each circuit and the system supply can support the alarm load safely.
2) Should I enter current in amps or milliamps?
Enter device currents in milliamps (mA) as listed on datasheets. The calculator converts to amps and totals per circuit and system automatically for sizing checks and exports.
3) Why does the calculator use alarm current for voltage drop?
Voltage drop is most critical during alarm because current is highest. Using alarm current helps reveal worst-case end-of-line voltage and highlights circuits that may fall below device minimum voltage.
4) How do I choose the safety margin percentage?
Use your project specification or authority requirements. A common range is 10–30% to cover tolerances and future expansion. Avoid exceeding equipment limits even if margin suggests a larger supply.
5) What does the battery derating factor represent?
Derating accounts for real-world battery capacity losses from temperature, aging, and discharge behavior. Lower values increase required amp-hours, providing more conservative sizing for compliance and reliability.
6) My devices are distributed along the run. Is this voltage drop accurate?
This is a simplified estimate using total circuit current and full loop length. For long runs with many tap points, a segmented calculation may be required to model current reduction along the circuit.
7) Why does a circuit show CHECK even when current is below rating?
Circuit rating checks current capacity, while CHECK indicates voltage performance. A circuit can be under current rating yet still fail minimum voltage at the far end due to length and conductor resistance.