220V to 230V Buck-Boost Transformer
Machinery built to a 230V nameplate does not always tolerate the 220V it finds when it lands in a US building. Choose the system phase and equipment nameplate amps below to see an available, buyable unit.
Load current (amps)
Quick answer
- Measured input
- 220V
- Required output
- 230V
- Correction
- Boost (raise voltage) · 4.5%
- Size from
- System phase and equipment nameplate amps
Technical details
220V to 230V technical overview
Machinery built to a 230V nameplate does not always tolerate the 220V it finds when it lands in a US building. A 220V to 230V buck-boost transformer closes that 10 volt gap, a correction of roughly 4.5%, without touching the machine or the service. It is the smallest of the common boost steps and the one most often specified for imported production equipment, drive-fed loads and instrumentation with a narrow stated input window. Single-phase and three-phase versions are offered in 10, 15, 20, 30, 40, 50 and 60 amp selections, chosen by the phase and the measured current of the load.
Where 220V to 230V correction is used
230V is the IEC nominal voltage used across most of Europe and much of Asia, which is why so much imported equipment carries it. When that equipment is installed on a US 240V system that measures 220 under load, or on a service that was never quite 240 to begin with, the machine spends its whole life at the bottom of its input range. Typical installations include European and Asian CNC and machining centers, packaging, labeling and case-erecting lines, injection molding auxiliaries, textile and converting machinery, commercial bakery and espresso equipment, laboratory autoclaves, centrifuges and environmental chambers, print and finishing equipment, and water treatment skids delivered as prewired packages.
The other recurring case is the OEM integrator or millwright commissioning a machine on a site whose supply was never verified. The machine builder specified a voltage window, the site supplies something at the edge of it, and the resulting faults get blamed on the equipment.
Why this 220V to 230V voltage pair matters
A machine specified at 230V plus or minus 5% has a floor of 218.5V, which means a building sitting at 220V has less than two volts of margin before it is formally out of specification. Nothing dramatic happens at that margin, and that is exactly the problem. The failures are intermittent rather than absolute: drives tripping on DC bus undervoltage during acceleration, control power supplies dropping out on contactor inrush, servo faults during rapid deceleration, heaters that never quite reach setpoint. A three-phase drive's DC bus sits at roughly 1.35 times the incoming line voltage, so 220V produces about 297V on the bus where 230V produces about 311V, and undervoltage thresholds are set relative to rated input rather than to what the building happens to deliver. Correcting 220 to 230 also removes one variable from every troubleshooting conversation with the machine builder.
Installation notes
Sizing guidance
Start from the machine's electrical data plate or the electrical schedule in its documentation, not from the disconnect rating. Confirm three things:
- The stated input window. A 230V nameplate with a plus or minus 5% window and one with a plus or minus 10% window are different problems, and only one of them may need correcting.
- Measured line-to-line voltage at the machine disconnect during its heaviest cycle step, not at idle. Machines with hydraulic pumps, vacuum systems or heat zones look very different mid-cycle.
- Total current at the correction point, including auxiliaries such as chillers, dust collection and material handling if they are fed from the same disconnect.
Add 25% for continuous loads and round up to the next available amperage among 10, 15, 20, 30, 40, 50 and 60. Because the transformer handles only the 10 volt difference and not the machine's full power, the correct unit is far smaller than the load's own rating, which is what makes a small correction like this economical to install at all.
Installation notes
Imported equipment brings one caveat that matters more here than on any other pair. A buck-boost transformer is an insulating transformer reconnected as an autotransformer, so there is no isolation between input and output, and it cannot convert a 3-wire delta supply into a 4-wire wye. A machine expecting 230V line to neutral, or expecting a specific earthing arrangement from its home market, does not get either one from a buck-boost transformer. It gets a corrected phase-to-phase voltage and nothing else.
Three-phase corrections use two units in open delta, which derives no neutral. Take control power from ahead of the correction or from a dedicated control transformer. Size conductors and overcurrent protection per NEC Article 450 and the applicable branch-circuit rules, and confirm the corrected voltage at the machine terminals under load before handing the equipment back over.
Common questions
- Can 230V equipment run on 220V?
Usually it will run, but often at the edge of its rating. 220V is about 4.3% below a 230V nameplate, which is inside the plus or minus 10% tolerance NEMA MG-1 allows for motors but outside a plus or minus 5% input window if the equipment manufacturer specified one. Equipment with drives, switch-mode power supplies or heat zones is the most sensitive, because it tends to fault intermittently rather than fail outright.
- Is a 4.5% voltage correction worth installing a transformer for?
It is when the load has a narrow input window. A 4.5% correction is not about efficiency, it is about moving equipment from the edge of its specified range back into the middle of it. On a machine specified at 230V plus or minus 5%, the difference between 220V and 230V is the difference between roughly two volts of margin and roughly eleven, which is what determines whether it faults on a hot afternoon.
- Does a buck-boost transformer isolate imported equipment from the supply?
No. A buck-boost transformer is an insulating transformer reconnected as an autotransformer, so the output shares a winding with the input and is not electrically isolated from it. It corrects voltage only. Where a machine requires galvanic isolation, a separately derived system, or a different grounding arrangement than the building provides, an isolation transformer is the correct product.
- Will a buck-boost transformer give me 230V line to neutral?
No. A buck-boost transformer corrects the voltage between the conductors it is connected to and derives no neutral. A three-phase correction is made open delta and produces a corrected phase-to-phase voltage on a 3-wire system. Imported equipment that expects 230V from line to neutral, as found on a 400/230V wye system, needs a proper 4-wire source rather than a buck-boost transformer.