Three phase power for a mining site, in plain terms

A mining machine is an unusual electrical load: it draws close to its rated power continuously, twenty four hours a day, with almost no variation. Buildings are rarely designed for that, and the gap between what a site has and what a rack of miners needs is where most first deployments lose weeks. The good news is that the vocabulary is small.

Why three phase, and from what size

Single phase power delivers energy in one alternating waveform. Three phase delivers it in three, offset from each other, which means power arrives more evenly and the same copper carries substantially more of it. For a handful of machines single phase is workable. Above roughly ten kilowatts of continuous load it stops being sensible, and every large machine on the market today expects three phase.

The practical consequence is that a garage or a small workshop supply will not take a rack. Getting three phase to a building that does not have it is a utility job with a utility timeline, and that timeline, not the hardware, is usually what sets your energisation date.

The voltages, and which one your machines want

• 208 V three phase. Common in North American commercial buildings. Some air machines accept it, most current ones start at 220 V, and at 208 V a machine draws more current for the same power, so cabling and breakers get heavier and the cost per megawatt goes up.
• 240 V. Found in some regional supplies and in delta configurations. Check the machine's rated range rather than assuming.
• 277 V and 480 V. The North American answer for large sites. 480 V three phase feeds transformers and PDUs efficiently and is what serious builds specify.
• 380 to 415 V. The standard across most of Europe, Asia, the Middle East and Africa. Most modern hydro machines are built for this band.

This is the single most common ordering mistake we see: a machine specified for 380 to 415 V arriving at a 208 V site. It will not run, and the fix is a transformer nobody budgeted for. The input voltage line on every product page exists for exactly this reason, and it is worth checking twice before a purchase order goes out.

Sizing a circuit

Two rules do most of the work. First, continuous load: a mining machine is a continuous load by any electrical code you will meet, so the circuit is sized at 125 percent of the machine's draw, or equivalently loaded to no more than 80 percent of the breaker rating. A 3.4 kW machine on a 240 V circuit draws about 14 amps and wants a 20 amp breaker, not a 15.

Second, balance the phases. Three phase power only behaves if roughly equal load sits on each leg. A rack loaded two thirds on one phase runs hot, wastes capacity and trips breakers that look undersized on paper but are not. Plan the layout so that machines distribute evenly across the three legs, and check it with a clamp meter once the rack is live rather than trusting the drawing.

Transformers, panels and where the losses go

Between the utility connection and the machine there is usually a transformer stepping the incoming voltage down to what the machines want, a main panel, distribution panels and then PDUs at rack level. Each stage has losses, and each has a rating you should not run to the edge of. Budget five to eight percent of your total draw as overhead for transformer and distribution losses when you size the incoming service, and do not discover the number after commissioning.

Get the layout done before the hardware ships. The full sequence is in our note on sizing power and cooling before the hardware arrives, and the commissioning week itself is covered in the first 72 hours.

Power quality, the quiet killer

Power supply units fail from bad power far more often than from age. Voltage sag on a weak rural feed, harmonics from a large inverter installation, poor grounding, or a generator that never quite settles will all shorten PSU life, and the failures arrive in batches months after the cause. If your supply is anything other than a clean utility feed, log voltage for a week before you energise. It is the cheapest insurance on the whole project.