Single phase or three phase floor grinder: which power supply?

The power question comes up on almost every floor grinder enquiry: does the job need single phase or three phase? On UK sites the honest answer is usually single phase, and the reason has more to do with motor technology than the supply itself.

What is the real difference between single phase and three phase power?

Single phase power, the standard 230 V supply found in almost every UK building and via 110 V site transformers on construction sites, delivers power through one alternating current waveform. Three phase power, typically 400 V, delivers three overlapping waveforms and is normally found on larger industrial sites, workshops and some commercial units with a dedicated three phase connection installed.

Why does single phase cover most jobsites?

Because single phase 230 V, or its 110 V site transformer equivalent, is what almost every building and site already has. A domestic refurbishment, a shop fit-out, a school corridor or a housing site rarely has a three phase supply run to the work area, while a 230 V socket or a site transformer is standard kit on any UK job. Specifying a three phase machine for this kind of work means either finding power that is not there or hiring a generator, both added cost and hassle for no real gain.

Where does three phase actually make sense?

Three phase earns its place on very large, continuous areas run for extended hours, such as a big warehouse slab, a distribution centre floor or an industrial unit already wired for three phase equipment. In that context the supply is already available, the floor area is large enough to justify a heavier-duty machine, and sustained high-load running benefits from the more even power delivery three phase provides.

Does motor technology change the power question?

Yes, because a brushless motor changes what single phase power can actually deliver. A brushed motor loses a meaningful share of its torque under sustained load as the carbon brushes wear and friction increases, which is why brushed single phase grinders have historically struggled on demanding jobs and pushed some buyers towards three phase for extra headroom. A brushless motor removes that friction loss entirely: no carbon brushes, no mechanical contact wearing down output, and constant torque delivered across the working speed range for as long as the job runs.

What does constant torque mean for the operator?

It means the machine keeps cutting at the same rate from the first minute to the last, instead of slowing down as the session goes on. On a brushed machine, torque drop under load often shows up as the operator leaning harder into the grinder to keep progress steady, which adds fatigue and slows the job regardless of what the spec sheet promised on day one. A brushless single head concrete grinder holds that output on ordinary single phase power, closing much of the gap that used to justify stepping up to three phase.

Is a brushless motor more efficient on the same power draw?

Generally yes, because no energy is lost to brush friction or heat generated by mechanical contact. That efficiency means a brushless single phase machine can deliver more usable cutting power for the same current draw than an equivalent brushed unit, which matters on a site running off a single 230 V circuit or a 110 V transformer shared with other tools.

What about site transformers and safety?

A 110 V site transformer is not a different power type, only a safer, stepped-down version of the same single phase supply. UK sites commonly run hand tools off 110 V via a step-down transformer for electrical safety reasons, particularly where cables and connections are exposed to damp or damage. A grinder rated for site use and sealed against dust and water ingress, for example to an IP65 standard, is built with exactly this kind of environment in mind, whatever the supply voltage feeding it.

Does running from a 110 V transformer reduce grinder performance?

Not meaningfully for a well-specified machine, since the transformer supplies the same single phase current at a lower, safer voltage rather than restricting available power for the tool. The practical consideration is cable length and circuit capacity rather than the transformer itself: a shared circuit feeding several tools at once needs enough headroom for the grinder’s draw alongside dust extraction and lighting.

What should be checked before committing to a single phase setup?

Check the circuit, not just the socket. A single phase supply that also feeds a dust extractor, task lighting and a battery charger on the same run can trip under combined load even though the grinder alone would run comfortably. Confirming the available circuit capacity, and running the extractor and grinder on separate circuits where possible, avoids a nuisance trip halfway through a slab that then has to be restarted and re-levelled from a stop line.

How should the choice actually be made?

Start from the site, not the spec sheet. If the job runs off standard 230 V or a 110 V transformer, which covers the overwhelming majority of refurbishment, domestic and commercial floor work, a brushless single phase grinder handles sustained floor grinding without the torque drop that made older brushed machines struggle. Three phase stays a sensible option specifically for very large, continuous industrial areas already wired for it and run for long uninterrupted hours. Pair either setup with proper on-tool dust extraction: the extraction system, not the phase count, is usually the detail that decides how clean and how fast the job actually runs.