Voltage-drop arithmetic is straightforward, but incorrect inputs can produce a convincing-looking result that is not useful. These are the mistakes worth checking first.
The most frequent errors
Check that every value uses the units expected by the formula and that the circuit type is correct.
- Doubling a cable length that the calculator already treats as one-way
- Using cable diameter instead of cross-sectional area
- Mixing metres with kilometres
- Ignoring conductor operating temperature
- Using load power as though it were current
- Applying the single-phase formula to a three-phase circuit
- Treating voltage drop as the only cable-selection requirement
Sanity-check the answer
Compare the result with the supply voltage, the length of the route and a nearby standard cable size. A dramatic change caused by a small input adjustment is a signal to check the entered units.
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Professional guidance
This article provides general information only. Electrical installation design and verification should be completed by a competent person using the current regulations and manufacturer data.