Voltage dips and short power interruptions are common disturbances in AC power networks. A motor starting, short circuit, large load change, or network switching event can cause the supply voltage to fall for a few milliseconds, several cycles, or even several seconds.
For electronic equipment, these events can cause resets, communication loss, relay dropout, display failure, corrupted data, or complete shutdown.
IEC 61000-4-11 defines standardized immunity tests used to determine how electrical and electronic equipment responds to voltage dips, short interruptions, and short-term voltage variations on its AC power input.
Unlike surge or EFT testing, IEC 61000-4-11 does not inject a high-voltage transient onto the supply line. Instead, it temporarily reduces the AC supply voltage itself and monitors how the equipment under test reacts.
What Is IEC 61000-4-11?
IEC 61000-4-11 is part of the IEC 61000-4 series of EMC immunity test standards.
The current IEC 61000-4-11:2020 edition applies to equipment:
– Connected to low-voltage AC supply networks
– Operating at 50 Hz or 60 Hz
– Having rated input current up to 16 A per phase
It does not cover equipment connected to 400 Hz AC networks.
For equipment drawing more than 16 A per phase, voltage dip and interruption testing is covered separately by IEC 61000-4-34.
The standard provides a common test method, while the applicable product or generic EMC standard determines which test levels, durations, and performance requirements must actually be applied to a particular product.
Voltage Dip vs. Short Interruption
These terms describe different levels of supply reduction.
Voltage Dip
A voltage dip occurs when the AC supply falls below its normal level for a limited period and then returns.
The EUT may continue receiving power, but at a reduced voltage.
For example, if a 230 V product is tested at a residual voltage of 70%, the supply during the dip is approximately:
230 V × 70% = 161 V
The voltage has therefore dropped by 30%.
This distinction is important because a 70% residual-voltage test does not mean a 70% voltage reduction.
Short Interruption
A short interruption is a much deeper loss of supply.
IEC 61000-4-11 uses 0% residual voltage for complete interruptions. In practical terms, the EUT receives essentially no supply voltage during the defined interruption period.
The ability to ride through this condition depends heavily on the product’s internal energy storage and system design.
Understanding IEC 61000-4-11 Test Levels
IEC 61000-4-11 uses the rated supply voltage, UT, as the reference.
The standard includes residual voltage levels of:
– 0% UT
– 40% UT
– 70% UT
– 80% UT
These correspond respectively to voltage reductions of:
– 100%
– 60%
– 30%
– 20%
The preferred combinations depend on the electromagnetic environment class and product requirements.
For Class 2 environments, typical preferred voltage dip conditions include:
– 0% residual voltage for ½ cycle
– 0% residual voltage for 1 cycle
– 70% residual voltage for 25 cycles at 50 Hz or 30 cycles at 60 Hz
Class 3 adds more demanding conditions, including:
– 40% residual voltage for 10/12 cycles
– 80% residual voltage for 250/300 cycles
For short interruptions, the preferred Class 2 and Class 3 condition includes 0% residual voltage for 250 cycles at 50 Hz or 300 cycles at 60 Hz.
The product standard remains responsible for determining which test conditions apply.
Why Test Duration Matters
Voltage level alone does not determine how severe a dip is.
A reduction to 0% for half a cycle is very different from a 0% interruption lasting several seconds.
At 50 Hz:
– ½ cycle = 10 ms
– 1 cycle = 20 ms
– 10 cycles = 200 ms
– 25 cycles = 500 ms
– 250 cycles = 5 s
At 60 Hz, equivalent durations use a different number of cycles.
Short dips mainly test the ability of the power supply and DC bus to ride through momentary disturbances.
Longer dips can discharge bulk capacitors and expose weaknesses in:
– Power supply hold-up time
– DC-link capacitance
– Reset circuits
– Undervoltage protection
– Firmware recovery
– Relay and contactor control
This is why voltage dip immunity is closely related to the complete power architecture of the EUT.
Typical IEC 61000-4-11 Test Setup
A voltage dip immunity test system normally includes:
– Voltage dip / interruption generator
– Controlled AC source
– EUT
– EUT monitoring equipment
– Voltage measurement equipment
– Test control software
The generator must switch the EUT supply between the normal voltage and the specified residual voltage while maintaining the required timing and transition characteristics.
Before testing begins, the laboratory verifies that the generator can produce the required voltage level and duration under the intended load conditions.
The EUT is then operated in a representative mode while the voltage disturbances are applied.
This type of test is normally performed as part of a wider EMC compliance testing process together with other immunity evaluations.
What Engineers Monitor During the Test
A voltage dip does not always cause complete equipment shutdown.
Engineers should monitor all functions that are important to the intended operation of the product.
Typical failure symptoms include:
– MCU or processor reset
– Display blanking
– Communication interruption
– Relay dropout
– Motor or actuator stop
– Sensor reading errors
– Loss of stored data
– Output voltage instability
– Alarm activation
– Failure to restart automatically
Some products may temporarily lose function and recover automatically, while others may require uninterrupted operation.
The acceptable response is determined by the applicable product standard and specified performance criteria rather than by IEC 61000-4-11 alone.
Power Supply Hold-Up Time Is Often the Critical Factor
Many IEC 61000-4-11 failures originate in the product’s power supply.
When input voltage drops, the DC bus must continue supplying energy to downstream circuits.
A power supply with insufficient hold-up capability may cause the DC rail to fall below the minimum operating voltage of:
– Microcontrollers
– FPGAs
– Communication transceivers
– Sensors
– Relays
– Control circuits
Bulk input capacitance, converter topology, operating load, undervoltage lockout, and downstream capacitance all influence the result.
A product that survives a half-cycle interruption at light load may fail the same test at maximum rated load.
For this reason, the EUT should be tested in operating modes that represent realistic or worst-case power consumption.
Inrush Current Can Appear After the Voltage Returns
Engineers sometimes focus only on what happens during the dip.
The recovery period can be just as important.
When the supply voltage returns, discharged capacitors may draw a large charging current. Transformers can also experience significant magnetizing inrush depending on the phase at which voltage is restored.
This can lead to:
– Input fuse operation
– Protection circuit activation
– Rectifier stress
– Relay dropout
– Power supply restart problems
– Repeated reset loops
A product may therefore survive the reduced-voltage period but malfunction immediately when full voltage is restored.
IEC 61000-4-11 specifically treats short-duration disturbances as important because transformer saturation and capacitor charging can produce substantial inrush effects after a dip.
IEC 61000-4-11 Is Different from EFT and Surge Testing
Voltage dip testing is sometimes grouped together with other AC power-port immunity tests, but the disturbance mechanisms are very different.
IEC 61000-4-4 EFT simulates repetitive fast transient bursts caused by switching events such as relay or contactor operation.
See IEC 61000-4-4 Electrical Fast Transient (EFT) Test Guide.
IEC 61000-4-5 Surge evaluates immunity to higher-energy overvoltage events associated with lightning effects and power-system switching.
See IEC 61000-4-5 Surge Immunity Test Standard Explained.
IEC 61000-4-11, by contrast, changes the supply voltage itself.
A product can therefore pass EFT and surge testing while still failing voltage dip immunity because its power supply cannot maintain the internal DC rails during a temporary reduction in mains voltage.
Common Causes of Voltage Dip Test Failure
Frequent causes include:
Insufficient DC Bus Capacitance
The stored energy falls too quickly when AC input voltage is reduced.
Poor Power Supply Hold-Up Design
The converter stops operating before the required dip duration has ended.
Undervoltage Protection Thresholds
Protection circuits may shut down the system earlier than expected.
Reset Circuit Problems
A slow or unstable DC rail can cause repeated processor resets.
Firmware Recovery Problems
The hardware may recover correctly, but the software does not restart communications or normal operation.
Relay or Contactor Dropout
Electromechanical devices may release when the control voltage falls.
High Recovery Inrush Current
The EUT may fail when the supply returns rather than during the actual voltage dip.
These problems are different from the PCB coupling and transient suppression issues normally associated with IEC 61000-4-6 conducted immunity testing or EFT testing.
When IEC 61000-4-34 Should Be Used Instead
The 16 A per-phase limit is an important part of equipment selection.
IEC 61000-4-11 applies to EUT input current up to and including 16 A per phase.
For equipment with mains current exceeding 16 A per phase, such as larger industrial machinery, high-power converters, large UPS systems, and some charging equipment, IEC 61000-4-34 provides the corresponding voltage dip, short interruption, and voltage variation immunity methods. The current IEC 61000-4-34 consolidated edition also includes Amendment 2:2025.
This distinction should be checked before selecting a voltage dip generator because the required source current capability can change substantially.
Practical IEC 61000-4-11 Test Checklist
Before performing a voltage dip immunity test, confirm:
– Applicable product or generic EMC standard
– EUT rated voltage
– 50 Hz or 60 Hz supply
– Rated input current per phase
– Required residual voltage levels
– Required dip durations
– Short interruption requirements
– Single-phase or three-phase configuration
– EUT operating mode
– Maximum expected load
– Generator current capability
– EUT monitoring method
– Recovery behavior after each disturbance
– Pass/fail performance criteria
IEC 61000-4-11 testing should reproduce the required supply disturbance accurately while the EUT is operating under representative conditions. For engineers troubleshooting failures, both the behavior during the voltage dip and immediately after voltage recovery should be recorded, because the root cause may lie in hold-up capability, undervoltage protection, restart logic, or recovery inrush rather than in the disturbance generator itself.
