Power & Electrical

The power chain: transformer to miner

Grid power reaches a miner through a chain, and a tech works at the last two links of it. Utility medium voltage hits a step-down transformer, feeds switchgear and panelboards or overhead busway down each aisle, drops into a PDU (power distribution unit) at the rack or shelf, and finally reaches the machine through a whip (the short cord and connector). Your job is the PDU-to-miner end: matching voltage, seating connectors, respecting breaker limits, and never assuming a circuit is dead.

• Transformer: supplies the site distribution voltage; suitability depends on the exact miner and PSU.
• Busway or panelboard: distributes three-phase power along each row.
• PDU: breaks the feed into individual breaker-protected outlets (usually C19).
• Whip / cord: the model-approved connection from distribution to the miner, with separately verified source-side and miner-side connectors.
• Miner PSU: the built-in power supply that rectifies AC to DC for the hashboards.

Input voltage: match the exact model and PSU

Voltage, phase, frequency and input-current requirements differ by model and PSU. Confirm the installed unit's label and current manufacturer documentation before selecting a feed. A family name or connector fit cannot establish compatibility.

Single-phase vs. three-phase, and how rows are fed

Some miners are single-phase loads: it wants two hot legs (line-to-line) or one hot and a neutral (line-to-neutral), depending on the design. But rows are fed with three-phase power because it moves far more energy on smaller conductors. The PDU or busway splits three phases across its outlets so the load stays balanced across A, B, and C phases. Supply examples below apply only to compatible equipment; some hydro models require three-phase input:

• 208 V three-phase wye can provide 208 V line-to-line to compatible loads. Do not connect equipment whose rated range excludes 208 V.
• 415/240 V wye provides nominal 240 V line-to-neutral and 415 V line-to-line. The approved electrical design determines connection and protection for each load.
• Balancing phases matters: loading one phase far harder than the others wastes capacity and can trip protection. PDUs are wired to spread miners evenly across the three phases.

PDUs, busway, whips, and connectors

PDU ratings, outlets and protection vary by installation. Verify the source-side plug, miner-side connector, cord rating and equipment approval separately. C19/C20 is one connector pair, not a universal miner standard; Bitmain specifies a C20–P13 cable for the S21 and S19j XP in its power-cord adaptation instructions.

• C19 / C20: a connector pair used on some equipment. Use the exact manufacturer-approved cord and verify its current and voltage ratings; do not infer the miner inlet from its family name.
• Busway: overhead bus bar running each aisle with tap-off boxes; lets you add or move PDUs without pulling new conduit.
• Branch breakers in the PDU: protect each outlet individually and are the breaker you check first when one miner is dark.
• Cord condition: stop and report discolored, melted, unusually hot or loose connections. Isolate under the site procedure and remove damaged parts from service for authorized inspection, replacement and verification. Never reseat a browned connector and return it to use.

Current and continuous-load headroom

For standard-rated NEC-style continuous-load applications, 125% sizing corresponds to an 80% loading example. Properly applied 100%-rated assemblies have different conditions. Qualified electrical design determines the applicable conductor, breaker, assembly and site limits.

1. Review the manufacturer's maximum/input-current requirements and approved circuit design; a point-in-time measurement does not override them.
2. For a single-phase estimate, RMS current I = P / (V × PF). At unity power factor, 3500 W / 240 V is about 14.6 A; at illustrative PF 0.95 it is about 15.35 A. Neither PF value is an asserted miner specification.
3. For balanced three-phase total power, I = P / (√3 × line-to-line voltage × PF). Do not apply the single-phase formula to a three-phase total.
4. In the standard-rated 80% example, a 20 A circuit has a 16 A continuous-load ceiling. Confirm every applicable installation limit before adding or changing loads.

Balancing miners across breaker sections

A container or row is often split into breaker sections, and each section feeds a set of racks. The site's electrical design gives each section a planning target in kW. That target sits below the breaker's rating to leave headroom. When miners are deployed, they are placed so every section stays at or under its target. A model with higher wall power fills a section with fewer machines, so some slots stay empty on purpose. The Power balance tool in Technician Reference does this math for any section size and model mix, and prints a section worksheet.

1. Find the section's planning target. If you only have the total approved load, divide it by the number of sections.
2. Divide the target by one miner's wall power in kW (watts ÷ 1,000) and round down. That is the most miners the section can take.
3. Spread those miners evenly across the section's racks, putting any extra on the first racks.
4. For mixed models, multiply each model's quantity by its kW and add the results. The total must stay at or under the target.
5. Swapping one model for another changes the load by the difference in their wall power. Check the new total before the swap.

Inrush at power-on

The instant a miner energizes, its PSU capacitors charge like a near short-circuit, so the momentary inrush current is many times the normal running draw. One machine is no problem. A whole row snapping on at once can spike well past what the breakers and upstream gear are sized for and trip protection or nuisance-trip a feeder. That is why large sites stagger power-on instead of throwing one big switch.

Real power draw vs. nameplate, and efficiency (J/TH)

Nameplate wattage is a rated figure, not a promise. Actual wall draw drifts with ambient temperature, input voltage, firmware, and the specific tuning applied; makers commonly spec roughly +/-5% variance. A hotter room or a higher power profile pushes real draw up. Efficiency is measured in joules per terahash (J/TH), watts divided by hashrate, and lower is better. Circuit planning must meet manufacturer maximum/input-current requirements and the approved electrical design; measured draw helps verify operation but does not replace those requirements.

Power profiles: underclock, overclock, and power limit

Most miners and fleet firmware let you shift the machine between performance modes, and every shift changes the wall draw. Underclocking (or a low-power mode) drops frequency and voltage: less hashrate, but noticeably less power and better J/TH. Overclocking does the opposite: more hashrate, more heat, more draw, worse efficiency, and less breaker headroom. A power limit caps maximum watts for stability. A tech needs to know the profile a miner is set to, because it changes loading against the approved circuit limits.

Curtailment and demand response

Curtailment is intentionally cutting or lowering miner load on command, usually to relieve the grid or capture a demand-response payment when power prices spike. It is one of mining's superpowers: a fleet can drop to near zero in seconds and come back in minutes without harming a thing. When a curtailment order comes down, miners are put to sleep or into a low-power mode across the site, then woken when the event clears. This is a planned business action, not a malfunction.

• Sleep mode: miner powers down its hashboards to near-zero draw; low mode holds a reduced power target.
• Fleet tools (Foreman, Braiins, etc.) issue bulk sleep/wake and power-target commands, run scheduled curtailment windows, and log an audit trail.
• Smart selection: tools can curtail randomly to spread wear, or sequence shutdowns so the most efficient miners keep running longest during a partial cut.
• Restart behavior: after an event, controllers retry waking miners for several minutes since not all wake on the first command.

Electrical safety: never work it energized

Everything above is high-current AC that can kill you or arc-flash you. The rule is simple: establish an electrically safe work condition before you touch the copper. NFPA 70E treats de-energizing as the default; energized work is only for qualified persons when de-energizing is truly infeasible. As a technician you rack, cable, and swap machines, tasks that should be done on a dead circuit with the miner unplugged.

1. Confirm the task, authorization and exact equipment/site isolation procedure with the responsible team.
2. Authorized personnel identify and isolate all relevant sources and control stored energy using the required lockout/tagout procedure.
3. A qualified person verifies electrical isolation using the applicable procedure and suitable inspected test equipment. A switch position, dark LED or stopped fan is not proof.
4. Service begins only after safe conditions are established. Connection changes require isolation each time; never disconnect live board power connectors.
5. Complete the required inspection and personnel clearance before controlled return to service; re-isolate before further physical changes.