Voltage dips + interruptions (IEC 61000-4-11)
Guide - IEC 61000-4-11
IEC 61000-4-11 is the horizontal immunity test standard for voltage dips, short interruptions and voltage variations on the AC mains supply. Published by the International Electrotechnical Commission and maintained by Technical Committee TC 77, it provides the test method for equipment whose rated input current per phase remains at or below 16 A. Above that, IEC 61000-4-34 takes over with a method adapted to high-power equipment. The standard fixes neither test levels nor acceptance criteria: it defines the method, and the product or generic standards select the applicable combinations. This page sets out the structure of the test, the dip-duration matrix, mains-phase synchronisation, performance criteria, and the pitfalls observed in the laboratory.
Position in the IEC 61000-4 series
Section titled “Position in the IEC 61000-4 series”The IEC 61000-4 series groups the electromagnetic immunity test methods applicable to electrical and electronic equipment. Each part defines a method for a specific phenomenon. The parts most frequently applied in CE EMC marking are the following.
| Reference | Phenomenon | Application area |
|---|---|---|
| IEC 61000-4-2 | Electrostatic discharge (ESD) | All accessible ports, contact and air |
| IEC 61000-4-3 | Radiated radio-frequency electromagnetic fields | Radiated immunity, typically 80 MHz to 6 GHz |
| IEC 61000-4-4 | Electrical fast transient bursts (EFT/Burst) | Power and signal ports |
| IEC 61000-4-5 | Surge | Power and long signal ports |
| IEC 61000-4-6 | Conducted disturbances induced by RF | Power and signal ports, 150 kHz to 80 MHz |
| IEC 61000-4-8 | Power-frequency magnetic field | Sensitivity to 50/60 Hz magnetic fields |
| IEC 61000-4-11 | Voltage dips, short interruptions, variations (AC, up to 16 A per phase) | AC power ports |
| IEC 61000-4-29 | Voltage dips, short interruptions, variations (DC) | DC power ports |
| IEC 61000-4-34 | Voltage dips, short interruptions, variations (AC, above 16 A per phase) | High-power AC power ports |
| IEC 61000-4-39 | Resilience to long-duration interruptions | Equipment connected to the public network |
The 4-11 method is one of the most systematically applied immunity tests because it targets a real and frequent phenomenon on the public network: a transient short circuit on a medium-voltage line, a protection switching event, a motor start on a shared feeder, are enough to produce dips lasting tens of milliseconds to a few seconds. The test is required by EN 55035 (multimedia), EN 55024 (ITE), EN 60601-1-2 (medical, 4th edition), EN 61000-6-1 and EN 61000-6-2 (residential and industrial environments), and virtually every EMC product standard.
4-11 (up to 16 A) or 4-34 (above 16 A)
Section titled “4-11 (up to 16 A) or 4-34 (above 16 A)”The split between the two standards is based on the rated input current per phase of the equipment under test. The 16 A threshold has a practical justification: test generators capable of supplying the necessary energy above this value become significantly more complex and expensive, and switching and restoring voltage at high current requires distinct technical solutions (high-power electronic switching, larger programmable three-phase sources).
| Criterion | IEC 61000-4-11 | IEC 61000-4-34 |
|---|---|---|
| Rated current per phase | Up to 16 A | Above 16 A |
| Supply type | Single-phase or three-phase | Single-phase or three-phase |
| Covered phenomena | Dips, short interruptions, variations | Same phenomena, adapted to higher power |
| Typical generator | Programmable AC source or dedicated dip simulator, range up to a few kVA | High-power programmable AC source, dedicated three-phase bench, tens of kVA |
| Dominant EUT effects | PFC DC bus hold-up, controller restart | Overload of power devices, motor regulation drift, large-format inverter behaviour |
| Dip generation method | Electronic switching between two voltage levels | Programmable source with controlled transition |
| Reference product standards | EN 55035, EN 55024, EN 60601-1-2, EN 61000-6-x, vertical standards up to 16 A | Vertical standards for high-power industrial and tertiary equipment |
The 16 A per phase boundary is administrative: a product rated at 16.0 A stays inside 4-11, a product rated at 16.1 A moves to 4-34. In practice, test laboratories operate a 4-11 bench almost universally; a 4-34 bench is much rarer infrastructure, which can significantly extend scheduling lead time for affected products.
Three phenomena, three sub-tests
Section titled “Three phenomena, three sub-tests”The standard distinguishes three families of disturbance. Conflating them in the test plan quickly leads to a non-conformity or an incomplete dossier.
Voltage dips
Section titled “Voltage dips”A dip is a temporary reduction of the rated voltage to a residual value for a short duration, followed by a return to the rated value. The three defining parameters are the residual voltage (typically 70 %, 40 % or 0 % of Un), the duration (in mains cycles) and the phase angle of triggering (typically 0 degrees or 90 degrees in sine convention).
Short interruptions
Section titled “Short interruptions”An interruption is a special case of a dip at 0 % residual voltage but with a longer duration, typically several hundred cycles, that is several seconds. The distinction is conceptual rather than physical: the standard keeps it because acceptance criteria differ (a product may be tolerated as shutting down during a long interruption, whereas a short dip targets normal operation).
Voltage variations
Section titled “Voltage variations”Variations are slow transitions between two voltage levels. The typical shape is a downward ramp from Un to a lower value, a plateau, then an upward ramp back to Un. The test targets slow regulation loops, the effectiveness of active PFC stages, and the stability of internal references whose setpoint depends on input voltage.
Dip-duration matrix
Section titled “Dip-duration matrix”The typical dip and interruption matrix, as carried forward by product standards, crosses residual voltage against duration. The grid below represents the reference layout. A product standard selects the applicable combinations from it; not all cells are systematically applied.
| Residual voltage | 0.5 cycle | 1 cycle | 5 / 6 cycles | 10 / 12 cycles | 25 / 30 cycles | 50 / 60 cycles | 250 / 300 cycles |
|---|---|---|---|---|---|---|---|
| 0 % (interruption) | Short dip at 0 % | Short dip at 0 % | Dip at 0 % | Dip at 0 % | Dip at 0 % | Dip at 0 % | Short interruption |
| 40 % | n/a | n/a | Dip at 40 % | Dip at 40 % | Dip at 40 % | Dip at 40 % | n/a |
| 70 % | n/a | n/a | Dip at 70 % | Dip at 70 % | Dip at 70 % | Dip at 70 % | n/a |
| 80 % | n/a | n/a | optional | optional | optional | optional | n/a |
Reading notes. The first number in the columns "5 / 6" and following corresponds to the duration in cycles at 50 Hz, the second to the duration in cycles at 60 Hz: 5 cycles at 50 Hz equal 100 ms, 6 cycles at 60 Hz equal 100 ms too; the standard aligns physical durations across the two supply frequencies. The "250 / 300 cycles" cell corresponds to a short interruption of about 5000 ms at 50 Hz and about 5000 ms at 60 Hz. A residual voltage of 80 % appears in some product standards for lighter immunity checks; it is not systematic.
The residual voltage is expressed as the percentage of nominal voltage Un that the EUT retains during the dip. A residual voltage of 70 % means that the voltage presented to the EUT is reduced to 70 % of Un, not that the disturbance removes 70 % of the voltage. This convention is the reverse of one sometimes used in electrotechnical literature.
Synchronisation with the mains phase
Section titled “Synchronisation with the mains phase”The phase angle at which the dip starts strongly influences the transient response of the EUT, particularly switch-mode power supplies. The standard typically requires both extreme conditions.
| Triggering angle | Convention | Electrotechnical effect |
|---|---|---|
| 0 degrees | Zero-crossing of the sine wave | The dip starts when the instantaneous voltage is zero; the PFC DC bus capacitor keeps supplying the converter; hold-up time is fully exercised |
| 90 degrees | Peak of the sine wave | The dip starts at the peak of the voltage waveform, which is also the charging moment of the DC bus capacitor; the cut intervenes at maximum current, the DC bus collapses faster |
For a typical switch-mode power supply, the 90-degree test is generally more severe than the 0-degree test for short dips (1 to 10 cycles) because it interrupts the DC bus recharge cycle. The reverse can be true for products with a large hold-up capacity, where stored energy covers several cycles. The standard requires both tests precisely because passing one does not guarantee passing the other.
Asynchronous variants are foreseen for products whose phase-angle sensitivity is demonstrably negligible (purely resistive loads, linear transformer supplies). The test plan must document this justification; asynchronous mode is not the default.
EUT operating modes during the test
Section titled “EUT operating modes during the test”IEC 61000-4-11 requires the EUT to be tested in operating modes representative of intended use. The generic or product standard generally identifies three modes:
- typical-use mode: rated load as declared, display on, communication active as applicable, in the scenario described as nominal by the technical documentation;
- standby mode: reduced power, minimum consumption, the state in which the product waits for a wake command;
- full-load mode: maximum allowable current, output at the highest power level defined, the conditions that stress the DC bus hold-up most.
The full-load mode is often the most critical: the DC bus capacitor discharges faster at high current, the effective hold-up time is reduced. A product that passes at 30 % of rated load can fail at 90 % of rated load on the same dip. The test report must specify explicitly the mode in which each test was conducted; a mention of "normal mode" without operational definition is insufficient.
Performance criteria A, B, C
Section titled “Performance criteria A, B, C”The acceptance criteria are not fixed by 4-11 itself; they are defined by the generic immunity standard or the product standard referencing it. The classification structure is common.
| Criterion | Behaviour expected during the test | Behaviour expected after the test |
|---|---|---|
| A | Normal operation, performance maintained above the specified level | Normal operation without intervention |
| B | Temporary degradation allowed, performance may drop below the specified level | Automatic recovery without operator intervention |
| C | Loss of function allowed | Recovery acceptable after manual intervention (reset, restart) |
The applicable criterion depends on the severity of the disturbance. For the shortest dips (0.5 cycle, 1 cycle), criterion A is typically targeted whatever the residual voltage: the disturbance is short enough to be absorbed. For long-duration 0 % dips (25 to 50 cycles), criterion B is generally accepted: the product is allowed to enter a degraded mode and then recover. For short interruptions (250/300 cycles, around 5 s), criterion C is generally accepted: a manual reset after voltage return is tolerated.
Some recent editions of product standards (notably the 4th edition of EN 60601-1-2 and revised EN 61000-6-x parts) introduce a combined B + C criterion: automatic restart when voltage returns, without operator intervention, but accepting loss of function during the interruption. This evolution reflects the real expectation of users: a medical or industrial product should restart on its own after a mains outage without requiring an operator on site.
Test generator
Section titled “Test generator”The 4-11 test is typically performed with one of two types of generator.
- Programmable AC source: linear or switched amplifier, able to deliver a programmed output voltage point by point, with control of the triggering phase angle. This is the most flexible solution: the same source can serve 4-11 tests, frequency variations, harmonics, flicker, and other mains-related tests.
- Dedicated dip simulator: a specialised module inserted between the mains and the EUT, switching electronically between rated voltage and a residual value or full interruption. Simpler, generally cheaper, but limited to the dip/interruption function.
In both cases, the standard specifies precise characteristics for the speed of transition between voltage levels (rise and fall times), the stability of residual voltage during the dip, and the stability of nominal voltage before and after the dip. The test report must establish that the generator meets these characteristics; this verification is typically performed through the generator manufacturer's certified self-check, complemented by periodic metrological calibration.
Relationships with other methods
Section titled “Relationships with other methods”IEC 61000-4-11 covers AC power ports only. Depending on the product topology, several complementary methods enter the test plan.
IEC 61000-4-29 for DC ports
Section titled “IEC 61000-4-29 for DC ports”For a product with a DC input (12, 24, 48 V DC or other), the equivalent method is defined by IEC 61000-4-29. The structure parallels 4-11: dips, interruptions, variations, comparable performance criteria. Durations and residual voltages are adapted to DC constraints (no triggering phase angle, the concept is not meaningful on DC; durations sometimes expressed directly in milliseconds rather than cycles). A product supplied DC from an external AC/DC converter can be tested under 4-11 on the AC input of the converter, and under 4-29 on the DC input of the product; the test plan states which port is under evaluation.
IEC 61000-4-39 for long-duration resilience
Section titled “IEC 61000-4-39 for long-duration resilience”IEC 61000-4-39 covers resilience to long-duration interruptions, beyond the temporal scope of 4-11. It applies to equipment for which a prolonged outage (minutes to hours) must be supported without data loss, without degradation of the main function on restart, or with a controlled transition to a degraded mode. It is complementary to 4-11, which covers short-duration phenomena.
EN 50160 and network reality
Section titled “EN 50160 and network reality”EN 50160 is the European standard that statistically characterises variations encountered on public low-voltage and medium-voltage networks. It describes the actual environment: dips, interruptions, harmonics, frequency deviations, long-term voltage deviations. EN 50160 is not a product test standard; it describes the network, not the equipment. IEC 61000-4-11 provides the standardised test framework that represents a conservative envelope of phenomena described by EN 50160. A product passing the 4-11 test at the levels specified by its product standard is presumed to withstand the typical phenomena characterised by EN 50160.
Pitfalls observed in the laboratory
Section titled “Pitfalls observed in the laboratory”Without claiming to be exhaustive, several recurring issues appear in test reports.
- Cycles confused with milliseconds. The standard expresses durations in mains cycles. 25 cycles at 50 Hz equal 500 ms, but 25 cycles at 60 Hz equal 416.7 ms. A test report generated automatically by a generator configured for 60 Hz but read by an assessor assuming 50 Hz produces an erroneous reading. The actual frequency of the test supply must be documented.
- Forgotten phase angle. A product tested only at zero-crossing that passes may fail at 90 degrees, because the DC bus collapse is faster there. The standard requires both angles; a test plan that only performs one is incomplete.
- Partial residual voltages. Testing only at 70 % residual voltage misses defects that appear only at 40 % or 0 %. Product standards typically specify several residual values, and all must be covered.
- Hold-up assumed, not measured. The hold-up time of a switch-mode power supply depends on load current and on the actual value of the DC bus capacitor (itself subject to ageing and temperature drift). Assuming "the DC bus holds for 20 ms" without measuring it on the final product at full load leads to surprises in the final test.
- Standby mode not tested. The standard requires testing in modes representative of intended use. Standby mode is often overlooked, although it sometimes carries specific weaknesses (dormant supplies with low energy reserves, microcontrollers in deep sleep that must wake correctly when voltage returns).
- Confusion between 4-11 and 4-5. Surge (IEC 61000-4-5) is a transient impulse of lightning or switching origin, with a duration in the microsecond to millisecond range. The 4-11 dip is a slow voltage reduction with a duration in the millisecond to second range. The two tests are independent and required in parallel in most product standards. For the surge/burst pair, see the guide Surge and Burst IEC 61000-4-5 / 4-4.
- Product standard not pinned. The 4-11 method fixes the test, the product standard selects the levels. Starting a test campaign without first verifying which cells of the dip-duration matrix are required by the applicable product standard leads to over-testing (expensive) or under-testing (non-compliant).
See also
Section titled “See also”- Harmonics and flicker (IEC 61000-3-2 and 3-3): mains quality
- Radiated emissions EMC test: pre-scan and final scan
- HEMP and IEMI: IEC 61000-4-25 and hardened electronics
- SAR procedures: absorption rate (IEC 62209, EN 50360)
Connection with CE marking and the EMC Directive
Section titled “Connection with CE marking and the EMC Directive”The 4-11 test is required by virtually every EMC product standard harmonised under the EMC Directive 2014/30/EU. For the broader CE EMC test context, see the CE tests page and the RED tests page which applies to radio equipment.
For the definitions of the terms used on this page (dip, interruption, residual voltage, hold-up, criterion A/B/C, EUT, power port), see the glossary.
Going further
Section titled “Going further”This page covers the fundamentals of the 4-11 test. Several related topics deserve a dedicated page:
- 4-5 (surge) and 4-4 (burst), immunity tests for fast and slow transients,
- 4-29 (dips and interruptions on DC ports), for industrial and telecom equipment,
- the combined B + C criteria introduced by recent product standards,
- 4-39 (long-duration resilience) and its articulation with 4-11.
Sources & references
- IEC 61000-4-11 Electromagnetic compatibility (EMC), Part 4-11, Voltage dips, short interruptions and voltage variations immunity tests , IEC webstore.iec.ch/publication/4172
- IEC 61000-4-34 Voltage dips, short interruptions and voltage variations immunity tests for equipment with input current more than 16 A per phase , IEC webstore.iec.ch/publication/4185
- IEC 61000-4-29 Voltage dips, short interruptions and voltage variations on DC input power port immunity tests , IEC webstore.iec.ch/publication/4194
- EN 50160 Voltage characteristics of electricity supplied by public electricity networks , CENELEC www.cenelec.eu/
- IEC TC 77 Electromagnetic compatibility , IEC www.iec.ch/dyn/www/f?p=103:7:::::FSP_ORG_ID:1303
- EN 55035 Electromagnetic compatibility of multimedia equipment, Immunity requirements , CENELEC www.cenelec.eu/