A full-size air-cooled Bitcoin miner is a continuous load of roughly 3 to 4 kW on a 200–240 V class single-phase supply. Hydro and immersion machines are usually three-phase loads of 5 kW or more. To power one safely you need a supply voltage inside the model's published input range, a circuit sized for the current it draws around the clock, the right connector, and a sound earth connection.
Everything here is for planning and for briefing an electrician. Mains wiring, breaker sizing and three-phase distribution must be designed and installed by a qualified electrician to your local code.
Key points
- Current (A) = power (W) ÷ voltage (V) for single-phase, and power ÷ (√3 × line-to-line voltage) for three-phase.
- A miner runs 24 hours a day, so it is a continuous load. Under North American practice a continuous load may use only 80% of the breaker rating.
- Size for the published power plus its tolerance, not the typical figure.
- Standard 110–120 V outlets cannot run a full-size miner.
- Check the exact model's published voltage range, phase and input current. They differ between models.
Watts, volts and amps
- Watts (W) measure power, the rate at which the machine uses energy. This is what you pay for and what becomes heat.
- Volts (V) measure the supply voltage.
- Amps (A) measure current. Current determines the size of the wire, breaker and connector.
They are related by:
single-phase: P = V × I × PF so I = P ÷ (V × PF)
three-phase: P = √3 × V(line-to-line) × I × PF
PF is power factor, the ratio of real power to voltage multiplied by current. The examples assume PF ≈ 1, a reasonable approximation for power supplies with active power-factor correction. If the manufacturer publishes a lower figure, the current is slightly higher.
A miner's power supply draws roughly constant power, so the same machine needs more amps on 208 V than on 240 V.
Current for a single-phase miner
Illustrative machine: 3,500 W, single-phase, PF ≈ 1. The third column adds a 5% power tolerance (3,675 W), which is the figure to design around.
| Supply voltage | Current at 3,500 W | Current at 3,675 W | 3,675 W current ÷ 0.8 |
|---|---|---|---|
| 208 V | 16.83 A | 17.67 A | 22.09 A |
| 230 V | 15.22 A | 15.98 A | 19.97 A |
| 240 V | 14.58 A | 15.31 A | 19.14 A |
The last column is the minimum breaker rating that keeps the load at or below 80%, which applies under North American practice. On calculated current, the machine at 240 V fits within the 16 A continuous capacity of a 20 A circuit. At 208 V it does not, and it needs the next size up. A 230 V supply outside North America is sized by that country's rules instead.
Calculated current is a planning figure. Manufacturers also publish an input current, and it can be higher. Bitmain lists a 20 A AC input for the Antminer S21, a 3,500 W machine. If the electrician sizes on that published figure, the minimum breaker is 20 ÷ 0.8 = 25 A, which in practice means a 30 A circuit. The nameplate and the manufacturer's documentation decide the circuit, not this table.
Current for a three-phase miner
Illustrative machine: 5,500 W, three-phase, PF ≈ 1. The current shown flows in each of the three line conductors.
| Line-to-line voltage | Current at 5,500 W | Current at 5,775 W (+5%) |
|---|---|---|
| 400 V | 7.94 A | 8.34 A |
| 415 V | 7.65 A | 8.03 A |
| 480 V | 6.62 A | 6.95 A |
Worked for 400 V: 5,500 ÷ (1.732 × 400) = 7.94 A. The 480 V row applies only to models whose published input range includes 480 V. Many three-phase machines are limited to 380–415 V. See Three-Phase Mining Equipment.
Breakers and the 80% continuous-load rule
A breaker protects the wiring from overheating. It is chosen for the circuit, and the circuit is chosen for the load.
North American codes treat a load that runs at maximum current for three hours or more as continuous, and commonly limit it to 80% of the breaker rating unless the equipment is specifically rated for 100% continuous duty. A miner is continuous by any definition.
| Breaker rating | Continuous limit (80%) | Usable power at 208 V | Usable power at 240 V |
|---|---|---|---|
| 20 A | 16 A | 3,328 W | 3,840 W |
| 30 A | 24 A | 4,992 W | 5,760 W |
| 40 A | 32 A | 6,656 W | 7,680 W |
| 50 A | 40 A | 8,320 W | 9,600 W |
Usable power is the continuous limit multiplied by the voltage, for a single-phase circuit. Other regions follow their own codes, which typically size the circuit from the design current, the cable type and the installation method rather than a flat 80%. In every case the decision belongs to the electrician and the local code.
Cable sizing as a concept
A conductor's safe current, its ampacity, must be at least the rating of the breaker protecting it. Ampacity is not a single number for a given wire size. It depends on:
- conductor material and cross-section;
- the temperature rating of the insulation;
- ambient temperature, which is high in a room full of miners;
- how many loaded cables are bundled or share a conduit or tray;
- the installation method.
Heat and bundling both reduce allowable current, and mining installations have plenty of both. Long runs add a further check for voltage drop. The cord between the PDU and the miner is part of the circuit too: it must be rated for the miner's current and for the protection upstream of it.
Why 110–120 V circuits are unsuitable
Two separate reasons rule out an ordinary North American wall outlet for a full-size miner.
- Current. 3,500 W at 120 V is 29.17 A. A 15 A circuit carries 12 A continuously (1,440 W) and a 20 A circuit carries 16 A (1,920 W).
- Input range. The power supplies are not designed for it. Bitmain publishes an input range of 220–277 V for the Antminer S21, and MicroBT publishes 220–240 V for the WhatsMiner M60S+. Both are manufacturer-published figures.
A step-up transformer on a wall outlet does not help. It changes the voltage, not the power, so the 120 V side would still need to supply more than 29 A.
The exception is the class of small, low-power home miners built for household outlets. Check the published input range for the specific unit. For full-size machines in North America, see 220V Bitcoin Mining.
PDUs and connector types
A PDU (power distribution unit) takes one larger feed and splits it into several outlets, usually with a breaker per outlet or per bank and sometimes with metering. It is where the branch protection for each miner's cord normally sits.
Most air-cooled miners use IEC 60320 appliance connectors:
| Connector pair | IEC current rating | Typical use |
|---|---|---|
| C13 (cord) / C14 (inlet) | 10 A | Lower-power equipment, and miners that split their load across two inputs |
| C19 (cord) / C20 (inlet) | 16 A | Full-size miners with a single high-current input |
North American certifications assign these connectors somewhat higher ratings than the IEC figures. Use the rating marked on the actual cord and outlet.
Published examples: MicroBT's datasheet for the WhatsMiner M60S+ specifies an IEC C19 cable rated at least 16 A. Bitmain's specification for the Antminer S19k Pro lists two AC inputs at 10 A each, and its Antminer S21 specification lists one at 20 A.
Hydro and immersion machines are different. They are three-phase units and generally do not use C13 or C19 cords. Expect manufacturer-specific power connectors or cables terminated directly onto a PDU, busbar or terminal block. MicroBT's WhatsMiner M63S++ datasheet describes its power cable as custom made and rated at least 16 A, and Bitmain lists an LP34 power port on its rack-format U3S23H hydro unit. Use the manufacturer's cable set and have terminations made by an electrician.
See PDUs and power cables.
Power quality and grounding
- Voltage under load. Measure at the miner with everything running. A supply that reads 240 V unloaded and sags under load pushes current up and can fall outside the published range.
- Frequency. Published ranges cover 50 and 60 Hz supplies. Generator-fed sites need stable frequency and voltage regulation.
- Grounding. Every miner, PDU and rack must be connected to protective earth so that a fault trips the protection instead of energising the metalwork. Never use an adapter or cord that removes the earth connection.
- Connections. A slightly loose plug or terminal carrying 15 A around the clock will overheat. Discoloured plugs and warm connectors are warnings to act on.
- Surges and harmonics. Larger sites need surge protection and a distribution design that accounts for harmonic currents. This is engineering work for the site's electrical designer.
Do not bypass or oversize protection to stop a breaker from tripping. A trip means the circuit is overloaded or faulty.
Planning steps
- Find the published power, voltage range, phase and input current for the exact model and hashrate version.
- Add the published power tolerance.
- Calculate current at your actual supply voltage.
- Give those figures to a qualified electrician to size the circuit, breaker and cable to local code.
- Confirm the connector on the miner and order matching cords and PDU outlets.
- Plan heat removal. Every kilowatt the miner draws becomes about 3,412 BTU/h of heat.