Calculator Inputs
Example Data Table
| Source V | Min V | Load A | Distance ft | AWG | Safety Factor | Expected Use |
|---|---|---|---|---|---|---|
| 24 | 16 | 1.50 | 300 | 14 | 1.25 | Fire alarm notification circuit |
| 24 | 18 | 0.85 | 450 | 12 | 1.20 | Auxiliary powered devices |
| 24 | 17 | 2.10 | 220 | 10 | 1.25 | Heavy alarm load branch |
Formula Used
The calculator first finds circuit resistance from wire size, material, distance, temperature factor, and parallel conductor count.
Loop Resistance = ((Distance × Path Factor × Ohms per 1000 ft) / 1000) / Parallel Conductors
Voltage Drop = Design Current × Loop Resistance
End Voltage = Source Voltage - Voltage Drop
Percent Drop = (Voltage Drop / Source Voltage) × 100
For end loaded circuits, the path factor is 2. Current travels out and back. For evenly distributed loads, the calculator uses a reduced path factor.
How to Use This Calculator
Enter the Firelite panel or power supply voltage first.
Enter the lowest allowed device voltage next.
Add the total alarm load current in amps.
Enter the one way circuit distance in feet.
Select the installed wire size and conductor material.
Use a safety factor for design reserve.
Add terminal resistance when field splices are significant.
Press calculate and review the pass result.
Firelite Voltage Drop Planning Guide
Why Voltage Drop Matters
Firelite alarm circuits often serve horns, strobes, modules, relays, and auxiliary devices. Each device needs enough voltage during alarm operation. Long cable runs can lower the final voltage. High current makes the drop worse. Thin wire also increases resistance. This calculator helps check those limits before installation. It is useful for design review, service calls, and quick field checks.
Advanced Circuit Inputs
The tool includes common factors that affect real alarm wiring. You can select wire gauge, material, distance, load current, temperature correction, and parallel conductors. You can also add a safety factor. This helps account for future device additions or nameplate tolerance. A custom resistance box is included for special cable data. Use it when the cable manufacturer gives a tested value.
Fire Alarm Design Use
Fire alarm voltage drop checks should be conservative. Notification appliance circuits must work when the supply is under load. Strobes may fail if voltage is too low. Auxiliary powered devices may reset or chatter. A careful calculation protects the system from nuisance trouble and failed acceptance tests. Always compare the end voltage with the listed device operating range.
End Load and Distributed Load
An end loaded circuit assumes the full current reaches the farthest point. This is the conservative method for many checks. A distributed load assumes devices are spread along the route. It reduces the effective drop because not all current flows through the full length. Use the conservative setting when placement is uncertain.
Using the Result
The result shows circuit resistance, voltage drop, end voltage, percent drop, and maximum distance. If the result says review required, reduce distance, increase wire size, lower load current, split the circuit, or use another power supply. The CSV and PDF buttons help save the calculation with project records. Final approval should follow device manuals, local code, and the authority having jurisdiction.
FAQs
What is a Firelite voltage drop calculator?
It estimates voltage lost in Firelite alarm wiring. It compares the final device voltage with your selected minimum voltage limit.
Can I use this for notification appliance circuits?
Yes. It is useful for NAC horn, strobe, and horn strobe branches. Always verify device current and voltage ratings.
Why does wire size affect voltage drop?
Smaller wire has higher resistance. Higher resistance causes more voltage loss when current flows through the circuit.
What does end loaded mean?
End loaded means the full current is assumed to travel to the farthest point. This gives a conservative design result.
What safety factor should I use?
Many designers use 1.20 or 1.25 for reserve. Use your project standard, device listing, and local requirements.
Can I enter custom cable resistance?
Yes. Enter ohms per 1000 feet in the custom field. It overrides the selected wire table value.
Why is my result marked review required?
The end voltage may be too low. The percent drop may also exceed your selected limit. Check wire size and load.
Is this a substitute for official approval?
No. Use it for planning only. Final fire alarm designs should follow manuals, code, and authority review.