A looped robot power cable connecting a low-voltage source to a motor, with probes at the load connector.

What you need

Use documented wire resistance per meter, one-way length and measured load current. Keep testing within the circuit’s protected low-voltage limits.

Voltage drop at 0.1 ohm loop resistance. 1 A: 0.1 V; 3 A: 0.3 V; 6 A: 0.6 V.
Voltage drop at 0.1 ohm loop resistance. Original Academy diagram using illustrative values; not a measured hardware result.
Read the diagram as a data table
Values used in the illustration
Condition or componentV
1 A0.1
3 A0.3
6 A0.6

The calculation

R_loop = 2 × L × r_wire + R_contacts
ΔV = I × R_loop
P_loss = I² × R_loop

L is one-way meters, r_wire is Ω/m, R_contacts is total contact resistance and I is A.

Worked example

Illustrative numbers. Replace them with your measured inputs.

For L=2 m, r_wire=0.02 Ω/m, R_contacts=0.02 Ω and I=3 A, loop resistance is 0.10 Ω. Voltage drop is 0.30 V and cable-plus-contact loss is 0.90 W. At 6 A, drop doubles but heating becomes 3.6 W.

Try it step by step

  1. Trace the complete supply and return path and include each connector, protective device and switch contact.
  2. Calculate drop at normal and peak current, then compare the load voltage with its operating limits.
  3. Measure at the load during a representative transient, using instruments and probing methods appropriate to the circuit.
  4. Select wiring and connectors using current capacity, temperature, routing and protection requirements as well as voltage drop.

How to check the result

Investigate localized warm connections even when the total calculated drop appears acceptable.

Common mistake to avoid

This electrical calculation is not a cable-ampacity rule. Bundling, insulation, temperature and connector ratings can set stricter limits.

Reference reading

Primary references for the underlying models, APIs or application context. The worked numbers and plots above are educational calculations, not results reported by these sources.

Read our methods, limitations and safety notes.

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