Low-Voltage Cable Voltage Drop Estimator
Estimate two-wire DC cable voltage drop for access control, cameras, and control wiring from the cable data-sheet resistance.
Circuit and cable details
Enter the distance from the source to the load. The calculation includes the outgoing and return conductors.
Use the cable manufacturer's resistance value at the expected operating temperature.
Set the limit for the connected equipment; this is not a universal code limit.
Estimated load voltage
About this estimator
Enter the DC source voltage, load current, one-way route length, one-conductor resistance, and the connected equipment’s voltage-drop target. The estimator reports the drop, load voltage, and maximum one-way distance for the entered target.
This tool is intended for preliminary checks on low-voltage control, access-control, and camera circuits. It does not select a conductor or cable.
Method and assumptions
Loop resistance equals twice the one-way length multiplied by one-conductor resistance per 1,000 feet. Voltage drop equals load current multiplied by loop resistance. Load voltage equals source voltage minus the calculated drop.
The calculation assumes a steady DC load and equal outgoing and return paths. Use resistance data for the actual cable and expected temperature; do not substitute values from a different cable construction without checking its specifications.
Interpret the result
The pass/fail message compares the calculated drop with the target you entered. Choose that target from the connected equipment requirements or project design criteria. The displayed maximum length uses the same load, cable resistance, and target.
FAQs
Why is cable length one-way?
Enter the source-to-load distance. The calculation doubles that distance to include the outgoing and return conductors in the DC circuit.
Which resistance value should I use?
Use the cable manufacturer’s resistance value for one conductor at the expected operating temperature. Check the product data sheet and use consistent units.
Does this select a cable gauge or approve a low-voltage circuit?
No. This estimator checks voltage drop only. Verify conductor ampacity, power-supply capacity, transient demand, cable listing, equipment voltage limits, and the rules that apply to the circuit.
Sources
- Use the cable manufacturer’s technical data sheet for conductor resistance, cable construction, temperature rating, and equipment compatibility.
- Use the connected equipment documentation and project requirements to set the allowable load voltage or voltage-drop target.