UPS Output Voltage at 380 V or 400 V? A Setting Worth Getting Right

A question that reaches the inbox constantly: should the UPS output line voltage be set to 380 V or 400 V? Both settings work, but the reasoning behind each, and the practical consequences, deserve a clear explanation.

Where the Two Numbers Come From

• 380 V/220 V is the nominal low-voltage level in the Chinese grid, written into GB/T 156 and related standards. Domestic transformer taps and distribution equipment ratings are all designed around it.
• 400 V/230 V is the harmonized nominal value recommended by IEC 60038, used across Europe and in many international projects, and it is the default output setting on many imported UPS units.

So the choice is, at its root, a question of following the domestic nominal system or the IEC one.

The Case for 400 V, and Its Costs

The argument for it:

• It compensates cable voltage drop. The run from the UPS to remote distribution cabinets and on to rack PDUs is not short, and a 3%–5% drop at full load is common. Raising the UPS no-load output to 400 V lands the far end near 380 V at full load, so the end-of-line voltage sits closer to nominal.
• It matches the ratings of IEC-based projects and imported equipment, avoiding the finger-pointing that starts when nominal levels do not line up across the chain.

The cost:

• Loads near the UPS see elevated voltage at light load, possibly above 400 V. That stays within equipment tolerance, but sustained overvoltage shortens power supply life slightly.
• The gap to utility voltage widens. With UPS output at 400 V while the maintenance bypass and automatic bypass are fed from the 380 V utility, a transfer crosses a voltage step of roughly 5%. Most IT power supplies will not notice, but the STS transfer window and the synchronization of bypass contactors deserve a recheck.

The Case for 380 V, and Its Costs

The argument for it:

• It matches the utility nominal, so bypass transfers cross no voltage step, every point in the system sees the same voltage, and the operational mental load is smallest.
• Downstream distribution equipment, from breaker ratings to PDU metering, is verified against 380 V and nameplates agree everywhere.

The cost: voltage drop on long, high-current runs is your problem to solve, by upsizing cable cross-section or raising settings at the PDU end, because the UPS will not lift the voltage for you.

How to Decide

1. Default to 380 V. It matches the nominal system and keeps the whole chain consistent, which is the safest starting point.
2. Consider 400 V only when the supply radius is long, measured end-of-line drop exceeds limits, and cable upgrades are impractical. Treat it as a voltage-lifting measure, and simultaneously verify the bypass transfer voltage step and the light-load voltage near the UPS.
3. Be consistent across the entire site. The worst outcome is a few units at 380 V and a few at 400 V running mixed, with STS and parallel systems working across a voltage difference and troubleshooting becoming doubly confusing.
4. Server power supplies accept a wide input range (a single-phase 90–264 V platform is typical, and three-phase wide-range platforms go higher), so both 380 V and 400 V sit well inside tolerance. This choice affects system consistency and distribution verification, not whether servers survive.

In short: 380 V buys uniformity, 400 V buys end-of-line voltage. Default to 380 V, raise to 400 V only for special conditions, keep the site consistent, and verify the bypass path. Those four sentences settle the question.