Voltage drop

Voltage drop is the voltage lost along a conductor. It follows Ohm's law: drop equals current times resistance. The calculation uses the round-trip wire length (twice the one-way distance) and the conductor resistance per 1000 ft from NEC Chapter 9, Table 8. For any given wire size, the drop grows with higher current and longer runs. Low-voltage systems (12 V, 24 V and 48 V) are the most sensitive, but long circuits in higher-voltage systems can also have significant drop. Voltage drop is not treated as a safety issue, so the code sets no compliance limit. Industry practice keeps the overall system drop within 2% to 5%. Non-mandatory NEC fine-print notes suggest 3% per feeder or branch circuit and 5% total. Check voltage drop after ampacity is satisfied, because it is often the deciding factor in wire sizing below 100 V. When you upsize conductors, confirm that the lugs, terminals and box sizes can take the larger wire. Moving a battery system from 24 V to 48 V cuts the DC voltage drop impact to 25% for the same wire sizes. Fuses, breakers and switches can add up to 0.5%, and charge controllers can add another 1% to 4%. On an inverter AC output, CPS recommends keeping the drop below 2% of nominal voltage at full power. A high drop pushes the inverter terminal voltage toward its overvoltage trip point, which can cause nuisance disconnects when grid voltage is already high. Include conductor temperature rise and ambient temperature in the calculation. Also consider transient dips from high inrush loads such as motor starting. On utility feeders, regulators use line drop compensation to boost voltage for the line drop. PV installed near the regulator can mask the load current, which can cause low voltage further down the feeder.

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• sentence 6: support check: partial - CPS's <2% recommendation and the overvoltage-trip mechanism are in u24, but the passage says the inverter disconnects (example: 105% grid plus 3% drop), not specifically 'nuisance' disconnects. -->