Machine Design #22: Factory Power Supply – The Basics a Machine Designer Needs to Grasp

When designing automatic machines, many mechanical people focus on the mechanism, motor, cylinder, jig, frame, cover, sensor.

But when it comes to finalizing the power-supply spec, they tend to ask very late:

What power does this machine use? Single-phase or three-phase? AC200V or AC400V? Is a transformer needed? Where does DC24V come from? How many kVA does the servo need? Can it be used if exported to the US? Are UL, CE, UPS, SPD, noise filter needed?

Power supply is not only the electrical side's job. The machine designer also needs to understand enough not to choose the wrong motor, not to lay out the control box wrongly, not to forget the installation conditions, and not to make a machine that "runs in our shop but cannot run in the customer's factory".

This article records the basic knowledge of factory power supply, from a machine-design perspective: from factory voltage, single-phase vs three-phase, DC24V, switching supplies, servo/inverter, robots, UPS, noise/surge/harmonic, to power supply when exporting the machine abroad.

1. Why does a machine designer also have to understand power supply?

In an automatic-machine project, a power-supply error is usually not a small error.

If you choose the wrong voltage or wrong supply type, the consequences can be:

The motor lacks power.
The servo drive faults during acceleration.
The inverter does not match the factory voltage.
The control panel has to be redesigned.
The machine is exported but cannot be used in the customer's country.
The UPS does not have enough backup time.
The PLC or PC resets on a momentary power failure.
The sensor picks up noise from wrong wiring.
The customer requires UL/CE but the chosen components are unsuitable.
The project is delayed because you have to change electrical equipment, change the transformer, change the panel.

Mechanical design does not need to do the electrical designer's whole job. But at minimum you need to understand the power system to ask the right questions from the start.

2. High voltage and low voltage in a factory

A factory receives power from the utility company in various ways. Basically it can be divided into:

Low-voltage receiving
High-voltage receiving

In Japan, a commonly used threshold is a 50 kW contract.

Item	Low voltage	High voltage
Contract capacity	Under 50 kW	From 50 kW to under 2,000 kW
Supply voltage	100V / 200V	Usually 6,600V
Transformer on the customer side	Not needed, the utility manages the transformer	A separate cubicle / substation is needed
Electricity cost	Usually higher	The unit price is usually lower
Common places	Small houses, shops, small workshops	Medium and large factories, buildings, large production areas

With high voltage, 6,600V is brought into the factory, then transformed in a cubicle / キュービクル for use at 100V, 200V or other voltages.

With low voltage, the power is already transformed on the utility side before being supplied to the facility. Small workshops usually use this method because it does not require investing in a cubicle.

From a machine-design standpoint, this affects:

Whether the voltage is stable
Whether three-phase power is available
The factory's spare capacity
Whether a separate transformer is needed in the machine
Whether there is a power-quality requirement
Whether there is enough capacity to run the machine, robots, heaters, compressor, chiller

You should not wait until the machine is assembled to ask what power the factory has.

3. Three-phase is the main source for power in a factory

When the machine has a relatively large motor, pump, fan, conveyor, servo, robot or inverter, the main source is usually three-phase power.

Three-phase power has advantages:

Transmits large power more efficiently than single-phase.
For the same power, the current is smaller than single-phase.
Lower loss on the wires.
Creates a smooth rotating magnetic field for the motor.
Industrial motors are simpler, more durable and more efficient.

In a Japanese factory, a very common power source is:

Three-phase AC200V

Meanwhile, single-phase power is usually used for:

Lighting
Outlets
PCs
Small measuring devices
Some control power
Small auxiliary loads

A mistake to avoid is trying to use a large motor on a single-phase supply just because "there is an outlet there". A single-phase motor has a power limit, poorer starting capability, and is usually unsuitable for heavy industrial mechanisms.

If the machine has a large motor, you must confirm from the start:

Does the factory have three-phase power?
What voltage?
How much capacity can be supplied?
Is there a starting-current limit?
Is a separate MCCB or dedicated line needed?

4. Common low-voltage power types in Japan

In Japan, the common low-voltage supply types can be summarized as follows:

Supply method	Output voltage	Main application	Note
Single-phase 2-wire	AC100V	Old houses, small devices, lighting, small outlets	Simple structure
Single-phase 3-wire	AC100V and AC200V	Houses, shops, small workshops, lighting, outlets, small AC	Can take both 100V and 200V
Three-phase 3-wire	AC200V	Motors, industrial machines, industrial AC, power equipment	Common power source
Three-phase 4-wire	240V / 415V reference	Large factories, large buildings	Not the most common type in Japan, but common abroad

For an automatic machine, at minimum you need to clearly note the required supply on the specification:

AC100V single-phase
AC200V single-phase
AC200V three-phase
AC400V / AC415V / AC480V if exporting
DC24V for control
Frequency 50/60Hz
Required capacity in kVA or A
Whether neutral, earth are needed

You should not vaguely write "200V power" without saying single-phase or three-phase.

5. Switching power supply and linear power supply

PLCs, sensors, solenoids, relays, I/O, HMIs, some controllers… usually need DC power, especially DC24V.

To create DC24V from AC100V/AC200V, the control panel usually uses a DC power supply.

Two basic supply types:

Switching power supply
Linear power supply

5.1. Switching power supply

A switching supply converts power by switching a transistor on/off at high frequency.

Advantages:

High efficiency, usually around 80–95% or more.
Small size.
Light.
Less heat.
Reasonable price.
Very commonly used in FA.

Drawbacks:

Generates noise from high-speed switching.
Needs attention to grounding, noise filter, wiring layout.
For analog sensors or sensitive measuring devices, you need to carefully consider ripple/noise.

5.2. Linear power supply

A linear supply uses a transformer and a linear regulator circuit, where the excess voltage is dissipated as heat.

Advantages:

Low noise.
Clean output.
Suits measuring devices, analog, audio, devices very sensitive to noise.

Drawbacks:

Low efficiency, usually around 30–60%.
Hot.
Big and heavy.
Needs a large heatsink.

Quick comparison:

Criterion	Switching power supply	Linear power supply
Efficiency	High, about 80–95%+	Low, about 30–60%
Size	Small, light	Big, heavy
Heat	Less	More
Output noise	Higher	Very low
Application	PLC, sensor, FA equipment, control panel	Measuring devices, analog, areas needing very low noise

In modern machines, a switching power supply is usually used for the main DC24V. If there is an analog sensor or a very sensitive measuring circuit, you can add a low-noise supply or separate the supply in that area.

6. Why is DC24V the standard in the control circuit?

In FA, DC24V is almost the standard for the control circuit.

DC24V is used for:

PLC I/O
Sensors
Relays
Solenoid valves
Indicator lamps
Some HMIs
Safety relays
Some encoders
Communication devices
Small controllers

Reasons DC24V is common:

Safer than AC100/200V for the operator.
In the low safe-voltage zone in many design cases.
High enough to reduce the effect of voltage drop on the wire compared to DC5V/12V.
Better practical noise immunity than levels that are too low.
Global FA components support it heavily.
Easy to standardize the control panel.

A very basic principle:

AC power wires and DC/signal control wires must be routed separately as clearly as possible.

You should not bundle motor wires, servo wires, inverter wires together with weak sensor wires. Electromagnetic noise can make PLC inputs jump, sensors report wrong, analog values noisy or communication fail.

7. Power in the control panel: main circuit and control circuit

The control panel should be viewed as two main power groups:

7.1. Main circuit

Used for:

Motors
Servo drives
Inverters
Heaters
Pumps
Fans
Robot controllers
Chillers or large auxiliary equipment

The supply is usually AC200V three-phase in Japan, or AC400/480V in many other countries.

7.2. Control circuit

Used for:

PLC
Sensors
Relays
Valves
Safety circuit
HMI
Controller
Part of the communication

The supply is usually DC24V.

These two systems need to be clearly separated:

Separate protective devices
Separate terminals
Separately routed wires
Correct grounding and noise handling
Easy troubleshooting when a fault occurs

If the main circuit and control circuit are designed in a disorderly way, the machine can still run, but noise faults and hard-to-trace faults will increase a lot.

8. Important power components in the control panel

A basic control panel usually has the following power-related components:

Component	Role	Design note
Main breaker / MCCB	Cuts the main power, protects against overcurrent/short circuit	Choose by current, SCCR, market standard
Switching power supply	Creates DC24V for control	Calculate total load + 20–50% margin
Transformer	Steps down or creates a separate supply like an AC100V service outlet	Calculate VA, heat, protection
Circuit protector	Branches DC24V protection by group	So one faulty branch does not bring down the whole DC24V
Noise filter / EMI filter	Reduces noise transmitted through the supply	Install near the input, ground correctly
SPD	Protects against surge from lightning or large switching	Install at the panel input if needed
Terminal block	Distributes power	Needs clear circuits, labels, allowable current
Ground bar	Gathers earth/PE	Needs good bonding and easy measurement
UPS	Backup for PLC/IPC/HMI on power loss	Choose suitable load and backup time

For the DC24V supply, you should not just calculate "just enough current".

You should sum all loads:

PLC CPU
I/O modules
Sensors
Solenoid valves
Relays
Indicators
HMI
Communication
Safety devices
Optional equipment

Then add a margin of about 20–50% depending on the level of redundancy and the load characteristics.

If many solenoids or relays close at the same time, you need to check the peak current.

9. Power for inverters and servo motors

Inverters and servo drives should not have their supply chosen by feel.

For a motor, the kW rating is only one part. During acceleration, the servo or motor can need a much larger current than steady running. If the supply, breaker, contactor, cable, transformer or facility capacity is not enough, the drive can fault or the machine will not reach performance.

A preliminary formula for power supply capacity:

Power supply capacity [kVA] = Motor output [kW] ÷ (Motor efficiency × Drive efficiency × Power factor)

Where:

Motor efficiency: the motor efficiency
Drive efficiency: the inverter/servo drive efficiency
Power factor: the power factor

This formula is only preliminary. In real design, you need to look at the drive and motor manual because manufacturers usually have tables for choosing the breaker, cable, reactor, noise filter, regenerative resistor.

9.1. Peak current during acceleration

The servo needs large torque in the acceleration/deceleration phase. If the cycle time is short, the duty high, the load heavy, the axis vertical or the inertia large, the peak current is even more important.

You need to check:

Acceleration torque
Load inertia ratio
Peak current
RMS current
Regenerative energy
Drive overload capacity
Power supply capacity
The heat of the motor and drive

9.2. Regenerative energy and braking resistor

When the motor decelerates, the inertial load drives the motor to keep turning. At this point the motor can generate power back to the drive. This is the phenomenon of regeneration.

If this energy is not handled, the drive can report overvoltage.

Common handling ways:

Braking resistor / regenerative resistor
Regenerative unit
DC bus sharing between multiple drives
Reducing the deceleration rate if the process allows

For a vertical axis, heavy load, robot, index table, fast-running axis, the braking resistor should not be left to calculate at the end.

10. Power for industrial robots and AGV/AMR

Robots come in many types, and their power supply also differs.

10.1. Collaborative robot / cobot

Cobots usually prioritize easy installation. Many run on:

Single-phase AC100–240V
A power of a few hundred W to over 1 kW depending on the load
Can plug into a more common source than a large robot

So cobots suit small cells, retrofits, lines needing flexibility.

But you still need to check:

What power the controller requires
Peak power
Whether a separate earth is needed
Whether there are auxiliaries like a gripper, camera, pump
The total cell power

10.2. Large industrial robot

Large 6-axis, high-speed, heavy-load robots usually need:

Three-phase AC200V in Japan
Or AC400V class in many countries
A power of several kVA or more
A dedicated supply and dedicated protection

You need to look at the robot controller manual, not guess by the robot size.

10.3. AGV / AMR

AGV/AMR usually use a battery:

DC24V
DC48V
Lithium-ion battery
Charging station
Contact or non-contact charging

The point to note is not only the battery voltage but also:

Charging power
The number of robots charging simultaneously
The charger inrush current
The charging station location
Battery safety
Emergency stop and power isolation

11. Reference table of power sources and drive equipment in Japan

Power type	Commonly used equipment	Note
Single-phase AC100V / AC200V	Small motors, small servos, AC-input stepping drivers, cobots, PCs, measuring devices	Easy to source, suits small loads
Three-phase AC200V	Induction motors, industrial servos, inverters, large robots, pumps, fans, large conveyors	The standard power source in Japanese factories
DC24V / DC48V	DC motors, DC-input stepping drivers, AMR/AGV, control devices, battery systems	DC24V common for control; DC48V common in mobile robots

This table is only general guidance. When choosing the real machine, you still have to check each device's manual.

12. UPS: not just to "keep running", but to stop safely

In a factory, the following can occur:

Instantaneous voltage dip
Momentary power failure
Lightning
Large switching in the electrical system
A regional grid fault

Just 0.1 second can cause:

A PLC reset
An industrial PC shutting down suddenly
An HMI restart
Data being written getting corrupted
A vision PC losing results
A robot/controller alarm
The line stopping midway
A product being NG

A UPS supplies temporary power when the source is lost or dips.

In FA, the goal of a UPS is not always to keep the machine running for many minutes. In many cases the goal is:

The PLC saving its state in time.
The PC shutting down properly.
The machine returning to a safe state.
Not losing recipe/log data.
Not damaging the product being processed.
Not crashing the operating system.

13. What to look at when choosing a UPS for FA?

Some points to check:

13.1. Power-supply method

For an important system, an online UPS / double conversion / 常時インバータ給電方式 has the highest stability because the load is always supplied through the UPS's inverter.

Line-interactive or standby types may be enough for some light applications, but you need to consider the switching time and voltage stability.

13.2. UPS capacity

You need to sum the total power of the backed-up devices:

PLC
IPC
HMI
Network switch
Camera controller
Data logger
Safety controller if needed
Some valves or brakes if a state must be held

You should not put a large motor on the UPS without a clear reason, because the UPS would be very large and expensive.

13.3. Backup time

If you need 3 minutes to shut down, you should not choose a UPS that gives exactly 3 minutes. The battery ages over time.

A safe direction is to choose a backup time about twice the actual need, then verify under the real load conditions.

13.4. Battery maintenance

A UPS is not install-and-forget.

The battery degrades over time. Without a replacement schedule, when a real power loss comes the UPS may not hold the load.

You need a plan:

Periodic testing
Battery replacement
UPS fault alarm
Logging the UPS state to the PLC/PC if needed

14. Noise, surge and harmonics: power supply is not just voltage

A machine that runs stably needs power that is "clean enough" and properly protected.

Three common problems:

Noise
Surge
Harmonics

15. Noise and how to handle it

Noise can come from:

Inverters
Servo drives
Relay/contactor switching
Solenoid valves
Motor cables
Switching power supplies
High-frequency equipment
ESD
Nearby welding equipment

The noise-handling philosophy has three directions:

Reduce at the source
Block along the transmission path
Increase the noise immunity of the receiving device

Common measures:

Use an EMI/noise filter at the power input.
Fit a ferrite core if suitable.
Separate power wires and signal wires.
Use shielded cable for encoders, analog, communication.
Connect the shield per the manufacturer's guidance.
Use a reactor for the inverter if needed.
Correct grounding and bonding.
Do not coil excess motor/encoder cable randomly in the panel.
Place the inverter/servo away from weak analog areas.

In machine design, wrong wiring can turn a good component system into a machine with intermittent faults.

16. Surge and SPD

Surge is a voltage spike in a very short time. The source can come from:

Lightning
Switching a large motor on/off
Switching a contactor
A grid fault
Nearby high-power equipment

Surge can destroy:

A switching power supply
A PLC
A servo drive
A network device
A sensor
A PC
A measuring amplifier

The device used to protect is:

SPD – Surge Protective Device

An SPD detects abnormal voltage and discharges the surge energy to earth/ground, helping protect the equipment downstream.

The installation location is usually at:

The control panel input
The area where AC power comes in from outside
Communication or outdoor sensor lines if needed
Systems with a lightning risk or long lines

The SPD must go with good grounding. If the ground is not good, the SPD cannot work correctly.

17. Harmonics and inverters/switching power supplies

Harmonics are frequency components at multiples of 50/60Hz that appear in the current.

The source of harmonics is usually:

Inverters
Servo drives
Switching power supplies
UPS
Rectifiers
Power electronics equipment

If the harmonics are large, they can cause:

Transformer heating
Cable heating
Interference with other equipment
Reduced power factor
Effects on the factory electrical system
Violation of guidelines in some cases

In Japan there is a harmonic-suppression guideline / 高調波抑制対策ガイドライン. When the machine has a large-power inverter or many drives, you need to ask the electrical side to check whether a harmonic reactor, filter or other measure is needed.

For a small machine, you often do not have to calculate deeply yourself. But the machine designer needs to know this problem exists so as not to overlook it when the power is large.

18. Exported machines: voltage and frequency differ by country

When a machine is sold or transferred to another country, power supply is the first issue to check.

For example:

Region / country	Frequency	Common industrial three-phase voltage
Japan	50 / 60Hz	200V
USA	60Hz	208V, 230V, 480V
China	50Hz	380V
Germany	50Hz	400V
UK	50Hz	400V

Japan very commonly uses three-phase 200V, but Europe is usually 400V, and North America commonly sees 480V. If the machine is designed only for 200V, when brought abroad it may need a transformer or a change of all the input equipment.

You need to confirm from the start:

Country
Voltage
Frequency
Phase
Grounding system
Plug/terminal requirement
Short-circuit current
Local regulation
UL/CE/CSA requirement
Spare parts availability

19. Multi-voltage: designing one machine for many countries

There are two main directions to make a machine usable in many countries.

19.1. Use an input transformer

The machine receives local power, for example AC400V or AC480V, then a transformer steps it down to AC200V for use by the internal equipment.

Advantages:

The panel components can be standardized to AC200V.
Easy to use familiar Japanese equipment.
Little need to change the servo/inverter if you only use the 200V class.

Drawbacks:

The transformer is big, heavy, hot.
The panel is larger.
The cost rises.
You need to calculate inrush, protection, heat.

19.2. Use wide-range-input equipment

Choose a switching power supply, inverter, servo drive with a wide input, for example AC200–240V or AC380–480V depending on the device.

Advantages:

Reduce or eliminate the transformer.
Smaller panel.
Easy to standardize internationally if you choose the right platform.
Reduced transformer loss.

Drawbacks:

The components can be more expensive.
You need to choose all equipment consistently.
Not every motor/drive supports a wide range.
You need to check the standards of each market.

There is no always-right way. A small machine can use wide-range. A machine using many Japanese 200V devices may need a transformer. A machine exported to many countries should plan for standardization from the start.

20. 50Hz/60Hz frequency and its effect on the motor

A very basic but dangerous mistake is using a motor at the wrong frequency.

An induction motor running directly on AC power has a speed nearly proportional to the frequency.

If you use 60Hz instead of 50Hz:

The speed increases by about 20%

Because:

60 ÷ 50 = 1.2

The effects can be:

The pump increases flow.
The fan increases air.
The conveyor runs faster.
The torque changes.
The motor heats up.
The mechanism runs at the wrong takt.
The machine vibrates or overloads.

Some motors clearly marked 50/60Hz compatible can be used at both, but you still have to look at the torque, current, speed, rating.

You must not use a 50Hz-only motor in a 60Hz region or vice versa if the manufacturer does not allow it. A mistake can cause overheating, motor damage, even fire.

If the motor runs through an inverter, you can actively control the output frequency. Then whether the input is 50Hz or 60Hz, the motor can still run at the same speed if the drive is configured correctly.

But you still need to check:

The inverter input voltage
Motor insulation
Cooling at low speed
The torque curve
Parameters
The fan/pump load characteristic

21. UL for North America: not just "having UL components"

When exporting a machine to the US or Canada, UL is a very important issue.

Legally, it can differ by product and region, but in actual transactions UL is usually almost mandatory because the customer, inspector, AHJ or factory requirement will ask.

For an industrial control panel, the commonly encountered standard is:

UL508A

The important points:

21.1. UL components

The main components in the panel such as:

Breaker
Power supply
Relay
Contactor
Terminal
Fuse
Wire
Drive
Transformer

need to be chosen with suitable certification, for example UL Listed or UL Recognized depending on the use position.

Not just any UL logo can be used anywhere. You need to look at the category, conditions of acceptability and the mounting method.

21.2. Wiring rules

UL508A has requirements on:

Wire size
Wire type
Wire color
Creepage/clearance distances
Branch-circuit protection
Terminal rating
Marking method
Enclosure
Overcurrent protection

21.3. SCCR

SCCR – Short-Circuit Current Rating is the short-circuit current value the control panel can withstand.

With UL508A, you need to calculate and note the SCCR for the panel. If the SCCR is lower than required at the customer's factory, the panel may not be allowed to be installed.

This is a part very easily overlooked if you are only used to making machines domestically.

21.4. cUL and CSA

Canada has CSA. Some products with cUL can be accepted in Canada as equivalent in many cases. But when actually exporting the machine, you still have to confirm with the customer and local standards.

22. CE for Europe: look at the whole machine, not just the panel

For Europe, a machine usually needs CE marking.

CE is not "a simple certification" in the sense that choosing a few CE components is done. CE is the manufacturer's declaration that the product meets the applicable directives.

For an industrial machine, it usually relates to:

22.1. Machinery Directive

Requirements on machine safety:

Guard
Interlock
Emergency stop
Risk assessment
Safety function
Prevention of mechanical hazards

22.2. Low Voltage Directive

Applies to electrical equipment in a certain voltage range, for example:

AC50V to 1000V
DC75V to 1500V

It relates to electrical safety, shock protection, fire, insulation, protection.

22.3. EMC Directive

Requires the machine to:

Not emit noise beyond the allowed level
Not malfunction due to external interference

This relates a lot to panel layout, grounding, shielding, filters, cable routing, inverter/servo and EMC testing.

The difference to remember:

UL usually emphasizes electrical safety, components and the panel in the North American way. CE looks at the whole machine and the applicable directives, including safety and EMC.

If exporting a machine to the EU, you should not wait until the end of the project to ask about CE.

23. Checklist when designing the power supply for a machine

23.1. Factory conditions

In which country is the machine installed?
What is the supply voltage?
Single-phase or three-phase?
Frequency 50Hz or 60Hz?
Is there a neutral?
What is the grounding system?
How much facility capacity can be supplied?
Are there harmonic, surge, noise requirements?

23.2. Power (main) supply

Does the motor use AC200V, AC400V or AC480V?
What is the servo/inverter input voltage?
Has the total kVA been calculated?
Has the peak current during acceleration been calculated?
Is there regenerative energy?
Is a braking resistor or regenerative unit needed?
Have the breaker, contactor, cable been chosen per the manual?

23.3. Control supply

Does the DC24V power supply have enough current?
Is there a 20–50% margin?
Is DC24V branched with circuit protectors?
Are PLC, sensor, valve, safety reasonably separated in supply?
Do sensitive analog/sensors need a separate supply or filter?

23.4. Noise and protection

Are power and signal routed separately?
Is an EMI filter needed?
Is a reactor needed for the inverter?
Is an SPD needed?
Are the ground bar and bonding clear?
Is the shielded cable handled correctly?
Is there a harmonic risk from many large drives?

23.5. UPS

Is backup for PLC/IPC/HMI needed?
How long a backup is needed?
Does the UPS have enough capacity?
Does the battery have a replacement schedule?
On power loss, how does the machine return to a safe state?
Does the UPS send a signal to the PLC/PC?

23.6. Export

Is a transformer needed?
Can wide-range input be used?
Can the motor be used at 50/60Hz?
Is UL508A required?
What is the panel SCCR?
Is CE required?
Is CSA/cUL needed?
Are the components easy to buy as replacements in the customer's country?

24. Conclusion

Power supply in a factory is not just "plugging in power so the machine runs".

It decides:

Whether the motor has enough force
Whether the servo faults during acceleration
Whether the PLC resets on a momentary power failure
Whether the sensor picks up noise
Whether the machine can be used abroad
Whether the control panel meets UL/CE
Whether the customer accepts installing the machine

The mechanical designer does not need to do the entire electrical part. But you need to understand the basic points to ask correctly, choose correctly and avoid locking the design into a wrong direction from the start.

A short sentence:

Power supply is a design condition, not a side task at the end of the project.

If you confirm the voltage, phase, frequency, capacity, standards and power quality early, the machine design will have far less risk.

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