What is the maximum allowable voltage drop per the Code?

The Quebec Construction Code, Chapter V — Electricity (section 8-102) limits voltage drop to 3% for a utilization circuit and 5% total (from the building entrance to the point of utilization).

To calculate voltage drop: ΔU = (2 × L × I × R) ÷ 1000 where L is length in meters, I is current in amperes, and R is conductor resistance in Ω/km. For example, a #10 AWG conductor (3.28 Ω/km) over 50 meters with 20 A gives ΔU = (2 × 50 × 20 × 3.28) ÷ 1000 = 6.56 V, or 5.47% at 120 V — too high. You need #8 AWG (2.06 Ω/km) for ΔU = 4.12 V = 3.43%, which is acceptable.

Excessive voltage drop causes motor overheating, reduced lighting, and premature equipment failure.