Voltage instability can damage appliances, interrupt industrial operations, and increase maintenance costs. Correct overvoltage and undervoltage protector settings help disconnect a circuit when voltage moves outside a safe operating range, reducing the risk of overheating, repeated motor starting, and premature equipment failure.
For 230V single-phase and 400V three-phase systems, the correct settings depend on the nominal supply voltage, connected load, grid stability, and equipment tolerance. This article explains how to configure an adjustable voltage protector without setting thresholds too tight or too loose.
Parameter setup and wiring should be completed by a qualified electrician according to local electrical requirements.
An adjustable overvoltage and undervoltage protector monitors the voltage supplied to a circuit.When the voltage rises above the configured upper limit or falls below the configured lower limit, the device disconnects the load.
After the power supply returns to a stable range, an automatic-reset protection device can restore power after the programmed reconnect delay.
These devices are commonly used in:
An overvoltage and undervoltage protector is designed for sustained abnormal voltage conditions. It does not replace a surge protective device (SPD) used for lightning-related or transient voltage spikes.
Before configuring the device, understand the main adjustable parameters.
The overvoltage trip value is the highest voltage allowed before the protector disconnects the circuit.
When the actual voltage remains above this value longer than the configured trip delay, the device cuts off power to help protect connected equipment.
The undervoltage trip value is the lowest acceptable voltage before the protector disconnects the circuit.
Low voltage can be particularly harmful to motors, pumps, compressors, and other inductive loads. It may cause overheating, low torque, poor starting performance, or excessive current draw.
Trip delay is the time the device waits before disconnecting the load after detecting abnormal voltage.
A very short delay provides faster protection, but it can also cause nuisance trips during brief fluctuations. A longer delay can improve operating stability but may leave equipment exposed to abnormal voltage for a longer period.
Reconnect delay is the waiting period before the protector restores power after voltage returns to normal.
This setting is especially important for compressors, refrigeration systems, pumps, and motor-driven equipment. Immediate restart after a voltage fault can cause high inrush current and repeated mechanical stress.
Do not apply the same settings to every project. Confirm the following conditions first.
Identify whether the system is:
The selected protector must match the voltage system and wiring method.
If you are unsure about the wiring configuration, review the differences between single-phase and three-phase power systems before selecting a protector.
Different loads react differently to voltage changes.
For example:
Measure the normal supply voltage during different operating periods, especially during peak load conditions.
When the local grid frequently fluctuates close to the protection threshold, the device may trip repeatedly. The settings should allow normal voltage variation while still protecting the load from harmful conditions.
Check the voltage tolerance stated by the equipment manufacturer.
The correct threshold should be based on the actual acceptable operating range of the connected equipment, not only the nominal system voltage.
For standard residential panels and light commercial applications, see our 220V adjustable overvoltage/undervoltage protector for a compact DIN rail solution.
A 230V single-phase system is common in residential, commercial, and light industrial applications. Typical loads include lighting, household appliances, pumps, small HVAC equipment, workshop tools, and control devices.
The following values can be used as general starting references for a 230V adjustable voltage protector.
| Parameter | Typical Starting Range | Purpose |
|---|---|---|
| Overvoltage setting | 250V–255V | Helps protect against sustained high voltage |
| Undervoltage setting | 190V–205V | Helps reduce low-voltage stress on equipment |
| Trip delay | 1–10 seconds | Helps avoid unnecessary trips from brief fluctuations |
| Reconnect delay | Based on load type | Prevents immediate restart after voltage recovery |
These values should be adjusted according to the actual grid condition and connected equipment.
For example, lighting circuits may use a shorter reconnect delay. Refrigerators, air conditioners, water pumps, and compressors usually require a longer delay to avoid repeated restarting.
For compact distribution boards, single-phase overvoltage and undervoltage protectors can provide practical DIN rail protection while allowing installers to adjust voltage limits for the actual application.
A 400V three-phase system is widely used for motors, compressors, pumps, HVAC equipment, factory machinery, and commercial distribution panels.
In addition to voltage thresholds, many projects require three-phase overvoltage and undervoltage protectors with phase-loss, phase-sequence, and phase-imbalance protection.
| Parameter | Typical Starting Range | Purpose |
| Overvoltage setting | 430V–440V | Helps protect three-phase equipment from high voltage |
| Undervoltage setting | 340V–360V | Helps reduce low-voltage motor stress |
| Trip delay | 1–10 seconds | Filters brief voltage fluctuations |
| Reconnect delay | Based on load type | Allows stable recovery before restart |
| Phase-loss protection | Enable when required | Helps protect three-phase motors |
| Phase-sequence protection | Enable for rotating loads | Helps prevent reverse motor rotation |
For a 400V system, one parameter set will not fit every load.
A motor-driven pump, refrigeration compressor, or production machine may need different protection logic from a general lighting or distribution circuit. Always confirm whether the selected device monitors phase-to-phase voltage, phase-to-neutral voltage, or both.
For projects requiring remote monitoring, a 3 Phase WiFi voltage protector with smart energy metering can combine voltage protection, current monitoring, energy metering, and remote control functions in one device.
Trip delay and reconnect delay should be matched to the load behavior.
For sensitive electronic equipment, a shorter trip delay may be preferred because the load can be affected quickly by abnormal voltage.
For motors and compressors, the protection strategy should focus on reducing repeated restart cycles. A suitable reconnect delay allows the system to stabilize before power is restored.
Consider the following principles:
The goal is not to make the protector react as fast as possible. The goal is to disconnect equipment only when voltage conditions become harmful.
If the undervoltage threshold is too close to the normal operating voltage, the protector may disconnect the circuit during normal voltage dips.
This can cause unnecessary downtime and repeated restart cycles.
If the upper voltage threshold is too high, equipment may remain connected during a harmful overvoltage condition for too long.
The setting should match the voltage tolerance of the load.
Automatic reset is useful, but immediate power restoration is not always safe.
Compressors, pumps, motors, and refrigeration equipment may be damaged or stressed by frequent restarting after short voltage interruptions.
An overvoltage and undervoltage protector does not replace a surge protective device.
For stronger distribution board protection, many projects use both:
When selecting an adjustable overvoltage and undervoltage protector, check the following requirements:
For intelligent distribution projects, a WiFi-enabled protector can be suitable where customers need both electrical protection and remote energy monitoring.
Correct overvoltage and undervoltage protector settings can help reduce equipment damage, avoid unnecessary downtime, and improve the reliability of power distribution systems.
For 230V systems, focus on actual grid voltage, connected load type, and suitable reconnect delay. For 400V three-phase systems, also consider phase loss, phase sequence, voltage imbalance, and motor operating conditions.
Liuyi Electric supplies single-phase and three-phase adjustable voltage protectors for residential, commercial, and industrial distribution applications. Request a voltage protection product recommendation and OEM/ODM quotation from our technical sales team.
For many 230V systems, an overvoltage setting around 250V–255V can be used as a starting reference. The final value should match local grid conditions and the voltage tolerance of the connected equipment.
A starting range of 190V–205V may be suitable for many 230V applications. Motor-driven and sensitive loads may require more specific settings.
For many 400V systems, an overvoltage range of 430V–440V and an undervoltage range of 340V–360V can be used as a starting reference. Always confirm the requirements of the equipment and local electrical standards.
No. It responds to sustained high-voltage and low-voltage conditions. A dedicated surge protective device is required for lightning-related and transient surge protection.
Yes, but the reconnect delay should be set carefully. Compressors should not restart immediately after every voltage interruption because repeated restarting can increase electrical and mechanical stress.
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