Press Brake Electrical Requirements: Voltage, Amps and Breaker Sizing
The electrical supply is the part of a press brake purchase that gets decided last and costs the most when it is wrong. This is how to read your panel and size the circuit before the truck is booked.
The supply types you will actually find in US shops
Before any calculation, identify what is in the building. North American supplies are not one thing, and the label on the panel decides what machine you can run:
- 120/240V split-phase, single phase — the standard for homes, garages and many light-industrial units. Two 120V legs give 240V across them. Common where no three-phase was ever run in.
- 208V three phase — the three-phase partner to 120/208V commercial distribution. Frequent in smaller commercial and mixed-use buildings, and a common supply for a 208V press brake.
- 240V three phase (delta) — a true three-phase supply at 240V line-to-line. Found in older or smaller industrial premises.
- 480V three phase — the workhorse of larger plants and modern industrial space. Moving the same power at 480V draws roughly a third of the current you would at 240V, so wiring is cheaper and runs longer. It is the supply a 480V press brake in a larger plant expects.
The useful question is never "what is common" but "what is in my panel". That is the constraint the machine has to meet, be built for, or be transformed to.
How to read your own panel
You do not need to be an electrician to gather the facts a supplier needs. Open the panel (dead, with someone qualified) and record:
- Voltage — read it off the main breaker or the utility meter. Note line-to-line value and whether it is single or three phase.
- Phase — three hot conductors plus ground is three phase; two hots plus neutral is split-phase single phase.
- Main breaker capacity — the amp rating of the service entrance breaker. This caps what any new machine can draw without a service upgrade.
- Spare capacity — a photo of the load schedule tells an electrician what amperage is free on which bus.
Photograph the nameplate and the panel. Those two images answer most of the electrical questions a supplier will ask you, and they prevent the "we assumed 480" conversation after delivery.
Calculating the current from motor power
Everything downstream of the motor rating is arithmetic. Convert the motor power to watts, then:
three phase: I = P ÷ (√3 × V × PF)single phase: I = P ÷ VPower factor (PF) is the ratio of real to apparent power. Use around 0.8 as a typical value for an induction motor unless the supplier gives a measured figure. Worked example, illustrative only and not a KECMT figure: a 15 kW hydraulic pump motor on 480V three phase at PF 0.8 draws
I = 15000 ÷ (1.732 × 480 × 0.8) ≈ 22.6 A√3 ≈ 1.732. This is a running-current estimate for the example motor. The actual starting (inrush) current of a hydraulic pump motor can reach several times the running value for the brief moments the pump accelerates — which is precisely why breaker and conductor sizing are not set to the running number alone.
Breaker sizing under the NEC 80% rule
A press brake hydraulic pump runs for extended periods, so under the National Electrical Code it is treated as a continuous load. The rule is that a circuit must be sized so the continuous load does not exceed 80% of the breaker rating — equivalently, the breaker (and the conductor) must be at least 125% of the continuous load. Using the example above:
breaker ≥ 22.6 A × 1.25 ≈ 28.3 A → next standard 30 AThe same 125% logic applies to the conductor ampacity. A breaker sized only to the running amps will nuisance-trip under real production heat, and a conductor sized the same way will run hot and age the insulation. "It turns on" is not the test; sustained, repeatable operation at your duty cycle is.
Voltage drop: the long-wire problem
Current is only half the story. Run a press brake on long, under-sized conductors and the voltage at the machine sags. A hydraulic motor starved of voltage loses torque and can stall under load; a CNC control seeing a drooping supply can reboot mid-cycle. As a rule of thumb, branch-circuit voltage drop is kept around 3% and total (service to machine) around 5% in typical practice — beyond that, motors and electronics misbehave. The conductor cross-section for your run length is a question to put to the supplier alongside the amp draw, because catalogue ampacity assumes a specific length.
Single phase and phase conversion, briefly
If your shop is single phase, you have three routes: buy a machine built for single phase (clustered at low tonnage), add a phase converter, or bring in three-phase service. On conversion:
- Rotary converters use an idler motor to generate the third leg. Robust, tolerant of load swings, and able to run more than one machine — but they draw idle current whenever energised.
- Digital (electronic) converters synthesise the third phase solid-state. Compact and quiet with no moving parts, but generally drive one motor at a time and are less forgiving of load spikes.
Either is enough for many small machines if sized generously against the pump motor. The full treatment, including duty cycle, is in the single-phase press brake guide.
Why voltage and transformer questions belong in the order
A 480V machine cannot simply be plugged into a 240V service, and a 240V machine cannot take 480V. The motor and control are wound for a voltage; the wrong one either will not start or will be damaged. The fix is a transformer, and a transformer sized for a press brake's inrush and continuous load is neither small nor off-the-shelf — it carries real cost and lead time. Stating your supply voltage in the order lets the builder ship the correct winding or bundle the right transformer. Discovering the mismatch during commissioning turns a one-day hookup into a weeks-long wait. The same logic applies in reverse for a low-voltage machine on a 480V service.
The electrical questions to ask the supplier
Put these in writing before delivery so your electrician quotes the hookup rather than guessing it:
- Full-load current at the voltage you actually have (not a nominal catalogue value).
- Their recommended breaker size and conductor gauge, stated for your supply and run length.
- Whether a transformer is required to match your service, and who supplies it.
- Energising requirements: control transformer, grounding scheme, any soft-start or specific fusing.
- Whether the motor is wired for your phase count, or needs a converter or rebuild.
If a seller cannot answer these, that is the answer. Tell us your supply voltage, available breaker size and the thickest material you need to bend, and we will tell you straight whether the circuit you have will support the machine — and what to ask your electrician.
Questions we get asked
What voltage are most US press brakes?
In North American industry the common three-phase voltages are 208V, 240V (delta) and 480V. 480V is typical of larger plants and lets you move the same power with less current; 208V and 240V show up in smaller buildings and commercial spaces. Single-phase 120/240V appears in light-industrial and garage shops. Press brake power requirements, press brake breaker size and press brake amp draw all come down to one question — not "what is common" but "what is in your panel", because that is what the machine has to match or be transformed to.
How do I calculate the amps a press brake draws?
From the motor power rating. For three phase: I = P ÷ (√3 × V × PF). For single phase: I = P ÷ V. Use power factor around 0.8 as a typical value unless the supplier gives you a measured one. These give running current; the starting (inrush) current of a hydraulic pump motor can be several times the running value, which is why the breaker and wire are sized with margin, not to the running number alone.
Why can't I just match the breaker to the running amps?
Under the NEC, a circuit serving a continuous load must be sized so the load does not exceed 80% of the breaker rating — equivalently the breaker must be at least 125% of the continuous load. A press brake hydraulic pump runs for extended periods, so it counts as continuous. A breaker sized only to the running amps will nuisance-trip under real production heat, and the wire sized the same way will run hot. Size for the rule, not the optimistic number.
Can a 480V machine run on a 240V service?
Not directly. The motor and control are wound for a voltage; feeding the wrong one damages them or simply will not start. You need a transformer, and a transformer sized for a press brake is not a small, off-the-shelf item — it has cost and lead time. That is why the supply voltage has to be stated in the order, not discovered during commissioning. The same logic applies in reverse for a 240V machine on a 480V service.
Do I need a phase converter for a small press brake?
Only if your shop has single-phase power and the machine is three-phase. A rotary converter uses an idler motor to synthesise the third leg and can run more than one machine; a digital converter does it electronically, quietly, and usually one motor at a time. Either works for many small machines, but size it generously against the pump motor, because hydraulic load spikes during the bend. See the <a href="/guides/single-phase-press-brake/">single-phase guide</a> for the full discussion.
What electrical questions should I ask the supplier?
Full-load current at your voltage, their recommended breaker size and conductor gauge, whether a transformer is required for your supply, and any special energising requirements (such as a control transformer or a specific grounding scheme). Get these in writing before delivery so your electrician quotes the hookup, not guesses it.
Still not sure what your power will support?
Tell us your supply voltage, available breaker size and the thickest material you need to bend. We will tell you straight whether single phase will do it.