Three-phase power is delivered on three line conductors whose voltages peak one third of a cycle apart. Mining sites use it for two reasons: it is how utilities supply large loads, and hydro and immersion miners of 5 kW and above are built with three-phase inputs. A site either spreads single-phase air-cooled miners evenly across the three phases or feeds three-phase machines directly. In both cases the supply voltage must match the machine's published input range.
Three-phase distribution must be designed and installed by a qualified electrician or electrical engineer to local code. This guide explains the calculations so you can specify equipment and check a design.
Key points
- Line-to-line voltage = √3 × line-to-neutral voltage. A 400 V system gives 230 V to neutral.
- Three-phase power: P = √3 × V(line-to-line) × I × PF.
- Single-phase miners should be distributed in equal numbers on each phase.
- Bitmain publishes a 380–415 V input for hydro models such as the Antminer S23 Hyd. On a 480 V or 600 V site they need a transformer. Some other manufacturers publish 380–480 V.
- Check the published voltage range, phase and input current for the exact model before designing around it.
Why large sites and hydro miners use three-phase
- Capacity per conductor. A three-phase 400 V feed at 32 A carries √3 × 400 × 32 = 22.2 kW on three line conductors. A single-phase 230 V circuit at the same 32 A carries 230 × 32 = 7.36 kW on two.
- Balanced load. When the three phases carry equal current, the currents cancel in the neutral, and the load on the transformer and generator is smooth.
- Utility supply. Services of hundreds of kilowatts and above are three-phase, and so are the transformers that feed them.
- Machine design. A power supply of 5 to 11 kW is built as a three-phase unit so that a single machine does not unbalance the supply. Bitmain, for example, publishes the Antminer S23 Hyd. at 5,510 W with a three-phase 380–415 V input.
Line-to-line and line-to-neutral voltages
A wye (Y) system has three lines and a neutral. Line-to-line (L-L) voltage is measured between two lines. Line-to-neutral (L-N) voltage is measured from one line to neutral. The designation gives both: 400Y/230 means 400 V L-L and 230 V L-N.
| System | Line-to-line | Line-to-neutral | Typical use |
|---|---|---|---|
| 208Y/120 | 208 V | 120 V | North American commercial buildings |
| 400Y/230 | 400 V | 230 V | Europe and many other 50 Hz countries |
| 415Y/240 | 415 V | 240 V | Countries with a 240 V nominal supply; also specified as a transformer secondary for 380–415 V equipment |
| 480Y/277 | 480 V | 277 V | North American industrial sites |
The two voltages are linked by √3 = 1.732. Nominal values are rounded: 120 × 1.732 = 207.8, 230 × 1.732 = 398.4, 240 × 1.732 = 415.7 and 277 × 1.732 = 479.8. Canadian industrial sites also use 600Y/347.
Which connection a single-phase miner uses depends on the system and on the miner's published range:
- On 400Y/230 and 415Y/240, miners connect line-to-neutral at 230 or 240 V.
- On 480Y/277, line-to-neutral is 277 V. That suits only models whose published range reaches 277 V. Bitmain publishes 220–277 V for the Antminer S21; MicroBT publishes 220–240 V for the WhatsMiner M60S+, which excludes it.
- On 208Y/120, miners connect line-to-line at 208 V, and only if the published range goes down to 208 V. Bitmain publishes 200–240 V for the Antminer S19k Pro.
The three-phase power formula
P = √3 × V(line-to-line) × I × PF so I = P ÷ (√3 × V × PF)
I is the current in each line conductor. PF is power factor; the examples assume PF ≈ 1.
Worked examples with an illustrative 5,500 W three-phase machine on a 400 V supply:
| Load | Calculation | Current per line |
|---|---|---|
| One machine, 5,500 W | 5,500 ÷ (1.732 × 400) | 7.94 A |
| Twenty machines, 110 kW | 110,000 ÷ (1.732 × 400) | 158.8 A |
| 1 MW at 415 V | 1,000,000 ÷ (1.732 × 415) | 1,391 A |
| 1 MW at 480 V | 1,000,000 ÷ (1.732 × 480) | 1,203 A |
For circuit sizing, use the manufacturer's published input current rather than a figure calculated from typical power. Bitmain publishes 12 A for the Antminer S23 Hyd. The calculated current at its typical 5,510 W and 400 V is 7.95 A, and at the bottom of the voltage range with the 5% power tolerance added it is 5,785.5 ÷ (1.732 × 380) = 8.79 A. The published figure is the one to design to.
Balancing single-phase miners across phases
Line-to-neutral connection (400Y/230, 415Y/240). Each miner's current flows in one line and returns through the neutral. An illustrative 3,500 W miner on 230 V draws 15.22 A. With equal numbers on each phase, the line currents are equal and the neutral currents largely cancel.
| Miners on L1 / L2 / L3 | Line currents | Neutral current |
|---|---|---|
| 4 / 4 / 4 | 60.87 A / 60.87 A / 60.87 A | About 0 A |
| 4 / 4 / 3 | 60.87 A / 60.87 A / 45.65 A | 15.22 A |
The neutral carries the imbalance. Power supplies also draw harmonic currents, some of which add in the neutral instead of cancelling, so the neutral is not a conductor to undersize. That is a design decision for the engineer.
Line-to-line connection (208Y/120). Each miner sits between two lines, so every line is shared by two groups of miners. With one 3,500 W miner on each of the three pairs, each miner draws 3,500 ÷ 208 = 16.83 A and each line carries √3 × 16.83 = 29.15 A. The check: 10,500 W ÷ (1.732 × 208 V) = 29.15 A.
Practical rules:
- Install single-phase miners in multiples of three per three-phase circuit.
- Use a PDU whose outlets are labelled by phase, and fill the phases evenly.
- Verify with per-phase current readings once the machines are running. Miners that are offline or in a low-power mode change the balance.
Why 380–415 V hydro machines need a transformer on 480 V or 600 V sites
Bitmain's published input range for the Antminer S23 Hyd. and S21 XP Hyd. is 380–415 V three-phase. North American industrial services are 480Y/277 in the United States and commonly 600Y/347 in Canada. Both are above the range, so the machines cannot be connected directly. Two solutions are standard:
- A step-down transformer from 480 V or 600 V to 415Y/240, sized for the mining load plus cooling plant.
- Specifying the main transformer at 415Y/240. A site that takes supply at medium voltage needs a transformer anyway. Ordering it with a 415Y/240 secondary avoids a second transformation and its losses.
A 415Y/240 secondary has a further advantage: the same distribution serves three-phase hydro machines at 415 V and single-phase air-cooled machines at 240 V line-to-neutral.
Not every hydro machine has this constraint. MicroBT publishes a 380–480 V input for the WhatsMiner M63S++ and M73, and Bitdeer states a 380–480 V three-phase input for its SEALMINER A4 hydro models. On a 480 V site those ranges include the supply voltage. The comparison is worth making before you choose a model, because a transformer adds cost, losses and lead time to a project.
Transformer capacity is rated in kVA: kVA = kW ÷ PF. An illustrative 1,000 kW of miners with 5% cooling overhead is 1,050 kW, about 1,050 kVA at PF ≈ 1 and 1,461 A at 415 V, before any design margin. Rating, impedance, protection and loading limits are engineering decisions. See transformers.
Three-phase PDUs
A three-phase PDU (power distribution unit) takes a three-phase feed and distributes it to the machines.
- For single-phase miners, the outlets (usually C19) are wired to alternate phases, line-to-neutral on 400 or 415 V systems and line-to-line on 208 V. Each outlet or bank has its own breaker.
- For three-phase machines, each output is a three-phase connection, made with the manufacturer's connector or a terminated cable.
Capacity follows from the formula. A 400 V, 32 A three-phase feed carries 22.2 kW:
| Load on a 400 V, 32 A feed | Total power | Current per line |
|---|---|---|
| Six 3,500 W single-phase miners, two per phase | 21.0 kW | 30.43 A |
| The same six at +5% tolerance | 22.05 kW | 31.96 A |
| Three 5,500 W three-phase machines | 16.5 kW | 23.82 A |
The first configuration fits on calculated current but has no margin once tolerance is included, and under the North American 80% continuous-load rule it would not be acceptable. If the miners' published input current is higher than the calculated figure, such as a 20 A input, two per phase would exceed a 32 A feed outright. Local code and the ratings of the PDU and its breakers decide.
When selecting a PDU, check the input voltage and current rating, per-outlet protection, per-phase metering so that balance can be verified, and the temperature rating for the hot side of the racks. See PDUs.