# Complete Guide to Voltage Drop in DC and AC Systems
Whether you are wiring a camper van, designing an off-grid solar system or running cable for garden lighting, there is one invisible enemy that can ruin your project before it starts: voltage drop. It is not just a technical nuance — it is the difference between a fridge that cools and one that shuts off, or between a safe installation and a fire hazard.# The Ohm's Law Formula Behind the Calculator
How Voltage Drop Is Calculated
The formula is ΔV = (2 × L × I × ρ) / S. L is the one-way cable length in metres, I is the current in amperes, ρ is resistivity (0.0178 Ω·mm²/m for copper, 0.028 for aluminium), and S is the cable cross-section in mm². The factor of 2 accounts for the current flowing out and back through the cable.
# Why 12V Systems Need Thicker Cable Than 230V
The Low Voltage Paradox
To deliver 1000W at 230V you only need 4.3A and a 1.5mm² cable will do the job. To deliver the same 1000W at 12V you need 83.3A, requiring 25mm² cable. The lower the voltage, the thicker the cable must be to carry the same power without dangerous losses. This surprises most camper van builders who assume 12V is safe to wire casually.
# Real Consequences of Excessive Voltage Drop
Heat, Failures and Fire Risk
A cable carrying too much current for its cross-section converts electrical energy into heat. Practical consequences: 12V fridges that shut off because they detect low voltage even with a full battery, LED strips that fade and yellow at the far end, motors that cannot reach rated torque, and in extreme cases, PVC insulation melting and causing fire.