240V to 200V Buck-Boost Transformers for 200V Equipment
Machine tools, injection molding machines, robots and semiconductor equipment built for the Japanese market are nameplated 200V, and a US 240V supply sits 20% above that. Choose the system phase and equipment nameplate amps below to see an available, buyable unit.
Load current (amps)
Quick answer
- Measured input
- 240V
- Required output
- 200V
- Correction
- Buck (lower voltage) · 16.7%
- Size from
- System phase and equipment nameplate amps
Technical details
240V to 200V technical overview
Machine tools, injection molding machines, robots and semiconductor equipment built for the Japanese market are nameplated 200V, and a US 240V supply sits 20% above that. A 240V to 200V buck-boost transformer closes the gap by removing the 40V difference. Because it is an insulating transformer reconnected as an autotransformer, and handles only that difference rather than the full load, it takes far less space and far less money than an isolation transformer sized to carry the same machine.
Where 240V to 200V correction is used
Imported production equipment is the driver here. Japanese three-phase machinery is built around a 200V nominal supply, and equipment from Korea and Taiwan is often specified the same way, so a machine crated for its home market arrives in a US shop with a 240V service waiting for it.
Equipment that regularly needs this correction includes CNC lathes and machining centers, wire EDM and laser cutters, injection and blow molding machines, industrial robots and their servo amplifiers, SMT placement and reflow equipment, printing and converting presses, packaging and labeling lines, and semiconductor process tools. Test and calibration benches use the same correction for a different reason, presenting a nominal 200V supply so a product can be evaluated at the voltage its own market uses.
The buyers are contract manufacturers, plastics processors, machine shops, electronics assemblers and university research groups, all of whom chose the machine for its capability rather than its supply voltage and now need the shop service to match it.
Why this 240V to 200V voltage pair matters
Two hundred volts is a design point, not a rounding of 208 or 220. Feeding a 200V machine from 240V puts it 20% over nameplate, which is double the plus or minus 10% NEMA MG-1 allows a motor, and well outside what the drive electronics expect.
Servo and spindle drives are the sensitive part. A drive rectifies the incoming line into a DC bus sitting at roughly 1.35 times the line-to-line voltage, so a 200V supply yields about 270V on the bus while a 240V supply yields about 324V. That difference eats the headroom the drive relies on for regenerative braking, and rapid deceleration can push the bus into an overvoltage fault. Barrel heaters, platen heaters and other resistive elements on the same machine run about 44% over their rated wattage, which upsets closed-loop temperature control and shortens element life.
Installation notes
Sizing guidance
Work from the machine's electrical documentation rather than a guess. Imported machinery normally carries a supply specification at the main disconnect or in the electrical schematic, giving a rated supply voltage, a phase configuration and a full-load or connected current. That current is the sizing input.
Confirm phase first. Most Japanese production machinery is three phase at 200V, though smaller benchtop and auxiliary equipment is single phase, and the two need different corrections. Then take the machine's rated supply current, add anything else that will run behind the same transformer, and choose the next amperage step above that total so spindle acceleration and simultaneous axis moves have margin.
The transformer processes only the 40V difference, so the unit supporting a large machining center is far smaller than the machine's connected load suggests. Rated supply current and phase decide the selection.
Installation notes
Frequency is unchanged. A buck-boost transformer corrects voltage only, so a 60Hz supply stays 60Hz on the output. Machines specified for 200V 50/60Hz operate normally once the voltage is right, but equipment that genuinely requires 50Hz needs a frequency converter, which is a different product entirely.
There is no isolation. The unit is an autotransformer, and the machine's supply terminals remain electrically connected to the building service. If the machine's documentation calls for a separately derived system or an isolation transformer for grounding or noise reasons, a buck-boost does not satisfy that requirement.
No neutral is created, so the 100V or 120V control circuits inside an imported machine still come from the machine's own internal control transformer fed off the corrected 200V supply. Three-phase corrections are made open delta. Apply overcurrent protection under NEC Article 450, size conductors from the ampacity tables, and confirm measured voltage at the machine's main terminals before commissioning.
Common questions
- Does a 240V to 200V buck-boost transformer also convert 60Hz to 50Hz?
No. A buck-boost transformer changes voltage only and passes frequency through unchanged, so a 60Hz supply remains 60Hz at the output. Most Japanese-built industrial machinery is rated 200V 50/60Hz and runs correctly on 60Hz once the voltage has been corrected. Equipment that genuinely requires 50Hz needs a frequency converter, which is a separate device.
- Can a buck-boost transformer supply the 100V circuits inside an imported machine?
No. A buck-boost transformer changes line-to-line voltage and cannot derive a neutral or a lower control voltage. The 100V or 120V circuits inside imported machinery are produced by the machine's own internal control transformer, which is fed from the corrected 200V supply. Nothing additional is required as long as the machine receives the supply voltage and phase configuration it was built for.
- Is 240V close enough to a 200V nameplate to run the machine as is?
No. 240V is 20% above a 200V nameplate, which is double the plus or minus 10% tolerance NEMA MG-1 allows for motors and outside the input range drive electronics are designed for. Resistive heaters on the machine would dissipate about 44% more power than rated, and servo drives would run with a DC bus roughly 20% high, cutting into the headroom available for regenerative braking.
- Should I use an isolation transformer instead for imported equipment?
Use an isolation transformer when the machine's documentation requires a separately derived system, when isolation is needed for grounding or noise reasons, or when the voltage change required is large. Use a buck-boost transformer when the job is correcting a supply by a modest percentage, since it is smaller and less expensive for the same load current. A buck-boost provides no isolation, because it is an autotransformer.