If you are asking how many volts is 3 phase, the direct answer depends on your region and measurement points, but the standard commercial values are 208V or 480V in North America, and 400V in Europe and the UK. These are line-to-line (L-L) voltages. The underlying assumption that fixes this answer is a Wye (Star) configuration, where the line-to-line voltage is exactly √3 (1.732) times the line-to-neutral (L-N) voltage. For example, in a standard European system, the math is straightforward: 230VLN × 1.732 = 398.36V (nominal 400V). In the US, a standard commercial panel yields 120VLN × 1.732 = 207.84V (nominal 208V).

The Core Formula and Neighboring Values

The foundational formula for converting line-to-neutral voltage to line-to-line voltage in a balanced 3-phase Wye system is:

VLL = VLN × √3 (where √3 ≈ 1.732)

However, grid voltages are rarely perfect. According to Electronics Tutorials, utility tolerances typically allow for a ±10% variance, but extreme brownouts or surges can push this to ±20%. If you are sizing control transformers or setting undervoltage relays, you must account for these neighboring values rather than just the nominal stamp on the panel.

3-Phase Voltage Neighboring Values (Based on 120V L-N Nominal)
Grid Condition Variance Line-to-Neutral (VLN) Line-to-Line (VLL) Impact on 3-Phase Motors
Severe Brownout -20% 96V 166V Stalling, high current draw, thermal overload trip
Standard Brownout -10% 108V 187V Reduced starting torque, slight temperature rise
Nominal (Target) 0% 120V 208V Optimal performance and efficiency
Overvoltage +10% 132V 229V Increased core losses, potential insulation stress
Severe Surge +20% 144V 249V Immediate risk of dielectric breakdown and MOV failure

How the Answer Shifts: 120V vs 230V vs 3-Phase

The confusion around 3-phase voltage usually stems from mixing up single-phase residential standards with 3-phase commercial standards. Here is how the answer shifts based on the system architecture:

  • 120V (Single-Phase, US Residential): This is a single phase referenced to neutral. There is no √3 multiplier here. You are measuring one leg of a split-phase 240V center-tapped transformer.
  • 230V (Single-Phase, EU/UK Residential): Similar to the US 120V system, this is a single phase referenced to neutral. It powers standard household outlets and has no 3-phase geometry.
  • 208V (3-Phase Wye, US Light Commercial): This is where the shift happens. You take three 120V L-N phases, offset by 120 electrical degrees, and measure between any two hot legs. The vector sum yields 208V, not 240V. This is a common trap for DIYers who assume two 120V legs will yield 240V in a 3-phase panel.
  • 400V (3-Phase Wye, EU/UK Commercial): The European equivalent. Three 230V L-N phases offset by 120 degrees yield 400V L-L.
  • 480V (3-Phase Wye, US Heavy Commercial/Industrial): Derived from a 277V L-N system (277V × 1.732 = 480V). This is the standard for large HVAC units, industrial lighting, and manufacturing machinery in North America.
Bench Tip: Never assume a 3-phase motor rated for "220/240V" will run happily on a 208V 3-phase panel. While 208V is within a 10% tolerance of 230V, the reduced voltage squared results in a ~20% drop in starting torque. If your load has high breakaway inertia, specify a 200V-rated motor or use a buck-boost transformer.

Decision Tree: Identify Your Exact 3-Phase Voltage

Use this decision path to lock in your exact system voltage and select the correct downstream equipment. Follow the if-then logic to reach your concrete specification.

Condition / Observation Then / Next Step Final Concrete Pick
IF you are in the US and measuring a large industrial facility or data center... THEN you are likely on a 480V Wye system. Verify by measuring L-N (should read ~277V). Pick: Specify a Square D EE45T3H (45kVA, 480V Delta to 208Y/120V) step-down transformer for your panel schedule.
IF you are in the US and measuring a retail strip mall, school, or office building... THEN you are likely on a 208V Wye system. Verify by measuring L-N (should read ~120V). Pick: Use Eaton BR250 50A 3-pole breakers for your 208V branch circuits.
IF you are in Europe/UK and measuring any commercial or industrial panel... THEN you are on a 400V Wye system. Verify by measuring L-N (should read ~230V). Pick: Select Schneider Electric iC60N 3-pole MCBs rated for 400V AC.
IF you measure ~120V on two phases to neutral, but ~208V on the third phase to neutral (US only)... THEN you have a 240V Delta High-Leg (Wild Leg) system. The high leg is mathematically 120V × √3 = 208V to neutral. Pick: You must use a Delta-configured 3-pole breaker and strictly avoid connecting any L-N 120V loads to the high leg (orange wire).

When This Conversion is Meaningless (Edge Cases)

While converting line-to-neutral volts to line-to-line volts is a strict geometric certainty (√3), there are specific scenarios where attempting a 3-phase conversion is entirely meaningless or physically impossible:

  1. When Power Factor (PF) is Unknown for Power Calculations: Converting volts doesn't require Power Factor. However, if your actual goal is to convert 3-phase volts into Watts (real power) or calculate Amps from a known wattage, the calculation is meaningless without the PF. The formula is P = √3 × V × I × PF. If you assume a PF of 1.0 for an inductive motor load that actually operates at 0.8 PF, your calculated current will be 20% lower than reality, leading to undersized wire and nuisance breaker trips.
  2. When the Configuration is Unknown (Wye vs. Delta): The √3 multiplier only applies to Wye (Star) systems when converting L-N to L-L. In an ungrounded Delta system, there is no neutral point. Measuring from a phase to ground will yield unpredictable, floating voltages dictated by capacitive coupling to ground, not a fixed mathematical ratio. As noted in the All About Circuits AC theory volume, attempting to apply Wye math to an ungrounded Delta will result in dangerous misconfigurations.
  3. When Measuring with the Wrong CAT Rating: If you are measuring a 480V 3-phase system with a CAT II multimeter, the reading is meaningless because the meter's internal arc-flash protection is insufficient for the available fault current. You must use a minimum CAT III 600V or CAT IV 600V meter (like a Fluke 87V) to ensure the reading is taken safely without the meter exploding under a transient spike.

FAQ: 3-Phase Voltage Quick Answers

Can I get 240V from a 208V 3-phase panel?
No, not directly. 208V is the maximum line-to-line voltage available. If you have a 240V-only appliance (like a commercial kiln or older HVAC compressor), you must install a 208V to 240V buck-boost transformer to make up the 32V deficit.

Why is 3-phase power preferred over single-phase for high voltage?
3-phase delivers constant power transfer (no zero-crossing power dips like single-phase) and uses less copper wire for the same wattage. A 3-phase system transmits the same power as a single-phase system using roughly 75% of the conductor weight.

What is the default recommendation for a new US commercial build?
Default to a 480V Y/277V service entrance. It minimizes voltage drop on long feeder runs and allows 277V LED lighting to run directly without step-down transformers, reserving a single 480V-to-208Y/120V transformer strictly for standard receptacle loads.