Every time a motor starts across town, your power supply takes a hit. Every time a fault clears on the distribution grid, voltage drops for a few cycles. Every time the UPS swaps from mains to battery, there’s a transition.
Most electronic equipment handles these disturbances without a hiccup. Some doesn’t. The difference is whether the equipment has been tested to the IEC 61000-4-11 and IEC 61000-4-29 standards — and whether it passed.
These two standards define how to test electrical and electronic equipment for immunity to voltage dips, short interruptions, and voltage variations. IEC 61000-4-11 covers AC supplies. IEC 61000-4-29 covers DC supplies. Together, they’re the foundation for immunity testing across industrial, commercial, and utility equipment.
This article covers what each standard requires, how the tests are performed, and how to interpret compliance claims on equipment you’re specifying or commissioning.
Table of Contents
Why Voltage Dip Immunity Matters
Power supply networks aren’t perfect. Even in well-designed utility grids, customers experience voltage disturbances regularly:
- Short-term dips from faults on adjacent feeders (cleared by protection in 60-200 ms)
- Momentary interruptions during automatic source transfer (from main feed to backup)
- Voltage variations during heavy motor starts or large load step changes
- Complete interruptions lasting from milliseconds to seconds during protection coordination
For a residential TV, these disturbances are invisible — maybe the picture flickers. For a protection relay, a PLC running a chemical process, or a hospital patient monitor, the same disturbance can trigger reset, data loss, or misoperation.
The IEC 61000-4 series (the “4” signifies testing and measurement techniques within the 61000 EMC family) provides a standardized way to verify that equipment handles these disturbances appropriately.
Two parts of the series specifically address voltage disturbances on power ports:
- IEC 61000-4-11 — AC input power ports (50/60 Hz networks up to 16 A per phase, rated input voltages up to 600 V AC)
- IEC 61000-4-29 — DC input power ports (rated DC voltages up to 360 V)
Both are classified as “basic EMC publications” under IEC Guide 107, meaning they provide the general test methods that product committees reference when writing equipment-specific standards.
IEC 61000-4-11: AC Supplies
Scope
IEC 61000-4-11 (current edition: 2004 with Amendment 1 from 2017) defines immunity tests for equipment connected to AC supply networks at 50 Hz or 60 Hz, with rated input current not exceeding 16 A per phase. This covers most residential, commercial, and light-industrial equipment.
What it doesn’t cover: 400 Hz aircraft systems, DC-only equipment (see IEC 61000-4-29), and equipment above 16 A per phase (usually covered by product-specific standards).
What it tests
Three types of disturbances on the AC input port:
1. Voltage dips — Sudden reduction of voltage below a specified threshold, followed by recovery. Characterized by residual voltage level and duration. For example, a “40% dip for 10 cycles” means the voltage drops to 40% of nominal for 10 cycles (200 ms at 50 Hz) then returns.
2. Short interruptions — Complete loss of voltage for a specified duration. Typically 0% residual voltage for durations from 0.5 cycles (10 ms at 50 Hz) up to several seconds.
3. Voltage variations — Gradual transition from rated voltage to a different level, maintained for a period, then return. Simulates slow changes due to load variations.
How the tests work
The equipment under test (EUT) is powered through a special test generator. The generator rapidly switches the EUT’s supply voltage to the specified disturbance level for the specified duration, then restores nominal voltage. The EUT’s response is observed and classified per the performance criteria (see below).
The voltage transition during dips and interruptions occurs at specified phase angles of the AC waveform — typically at zero-crossing for standard tests, but product committees can specify worst-case angles (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) for particularly critical equipment.
IEC 61000-4-29: DC Supplies
Scope
IEC 61000-4-29 (2000 edition) defines immunity tests for equipment with DC input power ports supplied by external DC networks. This specifically addresses equipment powered from:
- Station batteries in substations (typical: 24V, 48V, 110V, 125V, 220V DC)
- Telecom −48V DC distribution systems
- Industrial 24V DC control buses
- DC UPS distribution in data centers
- Solar/battery systems where loads run from DC
The standard applies to equipment supplied at DC voltages up to 360 V — covering the complete range of industrial DC systems used globally.
What makes DC testing different from AC
Two things that AC networks don’t have:
1. Battery vs charger as source. DC networks transition between sources (battery to charger, charger to battery) during normal operation. These transitions create voltage variations that don’t exist on AC systems.
2. Source impedance changes. During DC interruptions, the supply network can present either “high impedance” (switching between sources) or “low impedance” (fault clearing, reverse current flow). IEC 61000-4-29 tests both conditions separately.
What it tests
The same three categories as IEC 61000-4-11, adapted for DC:
1. Voltage dips — Reduction to 40% or 70% of rated DC voltage, for durations from 10 ms to 1 second.
2. Short interruptions — Complete loss (0% of rated) for durations from 1 ms to 1 second, tested under both high-impedance and low-impedance source conditions.
3. Voltage variations — Transition to 80%, 85%, or 120% of rated voltage, for durations from 100 ms to 10 seconds. These simulate battery discharge/charge cycles.
Key DC-specific requirement: ripple is separate
One important distinction: the ripple (AC superimposed on DC — from battery chargers) is explicitly excluded from IEC 61000-4-29 and is covered by IEC 61000-4-17 instead. If you’re testing a protection relay for battery charger ripple immunity, that’s IEC 61000-4-17 territory.
Test Levels: AC Power Ports
IEC 61000-4-11 defines preferred test levels and durations based on the equipment’s installation environment.
Voltage dips (50/60 Hz)
| Test Level | Duration (50/60 Hz) | Application |
|---|---|---|
| 0% U_T | 0.5 cycle (10 ms / 8.3 ms) | Critical — mandatory for all equipment |
| 0% U_T | 1 cycle (20 ms / 16.7 ms) | Very short interruption |
| 40% U_T | 10/12 cycles (200 ms / 200 ms) | Severe dip (remote fault) |
| 70% U_T | 25/30 cycles (500 ms / 500 ms) | Moderate dip |
| 80% U_T | 250/300 cycles (5 s / 5 s) | Minor sustained variation |
Notation: “U_T” is the rated test voltage. “40% U_T” means the voltage drops to 40% of nominal during the dip — so a 40% dip on 230 V nominal is actually 92 V, not a 92 V reduction.
“10/12 cycles” means 10 cycles at 50 Hz or 12 cycles at 60 Hz (both equal to 200 ms).
Short interruptions
| Test Level | Duration |
|---|---|
| 0% U_T | 250/300 cycles (5 seconds) |
Voltage variations (optional)
Transitions between rated voltage and 70% for defined durations, simulating load change effects.
Product-specific level selection
The test levels in IEC 61000-4-11 are a menu — the product committee responsible for each equipment type (IEC 60255 for protection relays, IEC 61131 for PLCs, IEC 60601 for medical equipment, etc.) specifies which combinations of level and duration apply to that equipment class.
Test Levels: DC Power Ports
IEC 61000-4-29 uses three separate tables for the three test categories:
Voltage dips on DC supplies
| Test Level | Duration |
|---|---|
| 40% U_T | 10 ms, 30 ms, 100 ms, 300 ms, 1 s |
| 70% U_T | 10 ms, 30 ms, 100 ms, 300 ms, 1 s |
Short interruptions on DC supplies
| Test Level | Test Condition | Duration |
|---|---|---|
| 0% U_T | High impedance AND/OR low impedance | 1 ms, 3 ms, 10 ms, 30 ms, 100 ms, 300 ms, 1 s |
The high-impedance test simulates switching between two sources (the DC bus goes open-circuit briefly). The low-impedance test simulates fault clearing on the DC bus (capable of absorbing reverse current from the load).
Voltage variations on DC supplies
| Test Level | Duration |
|---|---|
| 85% and 120% U_T, OR 80% and 120% U_T | 100 ms, 300 ms, 1 s, 3 s, 10 s |
Practical interpretation: For a 110 V DC substation battery, a 120% voltage variation means 132 V. An 80% variation means 88 V. The equipment must operate normally across this range for up to 10 seconds — simulating real battery voltage swings between discharge and float charge.
Test Generator Requirements
Both standards specify detailed requirements for the test generator to ensure consistent, reproducible results.
IEC 61000-4-11 (AC) generator specs
| Parameter | Requirement |
|---|---|
| Output voltage range | Up to rated test voltage, ±5% of residual value |
| Output current capability | 16 A RMS per phase at rated voltage |
| Current at 80% U_T | 20 A for 5 s |
| Current at 70% U_T | 23 A for 3 s |
| Current at 40% U_T | 40 A for 3 s |
| Voltage change with load | Less than 5% of U_T |
| Voltage rise/fall time | 1 μs to 5 μs (abrupt transitions) |
| Peak inrush current capability | Up to 1000 A (250–600 V mains), 500 A (200–240 V), 250 A (100–120 V) |
The inrush current spec is significant: equipment with transformers at the input can draw 10–40× rated current briefly when voltage returns after a dip. The test generator must handle this without voltage collapse.
IEC 61000-4-29 (DC) generator specs
| Parameter | Requirement |
|---|---|
| Output voltage range | Up to 360 V DC |
| Output current (steady state) | Up to 25 A |
| Voltage change with load | Less than 5% |
| Ripple content | Less than 1% of output voltage |
| Rise/fall time of voltage change | 1 μs to 50 μs |
| Overshoot/undershoot | Less than 10% of change |
| Peak inrush capability (low impedance mode) | 50 A at 24 V, 100 A at 48 V, 220 A at 110 V |
| Output impedance (high impedance mode) | ≥ 100 kΩ |
The ability to operate in both high-impedance and low-impedance modes during interruption tests is a defining characteristic of IEC 61000-4-29 test generators.
The Four Performance Criteria (A, B, C, D)
Both IEC 61000-4-11 and IEC 61000-4-29 classify test results using the same four-level scheme:
| Criterion | Description |
|---|---|
| A | Normal performance within limits specified by the manufacturer — no observable effect |
| B | Temporary loss of function or degradation that ceases when the disturbance ends — equipment recovers automatically, no operator intervention needed |
| C | Temporary loss of function or degradation requiring operator intervention (reset, restart, reconfiguration) |
| D | Loss of function that is not recoverable — damage to hardware, software, or data |
How product committees use these criteria
The product-specific committee defines which criterion applies to each test severity. For example, a protection relay standard might specify:
- Voltage dip, 40% U_T, 10 cycles → Criterion A (no performance degradation allowed)
- Short interruption, 0% U_T, 5 seconds → Criterion B (temporary reset acceptable, automatic recovery)
- Long interruption, 0% U_T, 60 seconds → Criterion C (operator reset after power restoration acceptable)
The critical distinction between A, B, and C
For protection relays specifically: The transition between criterion A and criterion B defines whether the relay keeps protecting the system during the disturbance. A relay that holds criterion A through a 5-cycle dip continues monitoring currents and can trip on a fault that develops during the dip. A relay that only meets criterion B resets during the dip and isn’t protecting for some period afterward.
This distinction is often invisible on a datasheet but critically important for protection engineers.
What Compliance Looks Like on a Datasheet
Reading EMC compliance on equipment datasheets requires translating standardese. Here’s what common compliance claims mean:
Example 1: Simple compliance claim
“Complies with IEC 61000-4-11 at test level 3”
What it means: The equipment passed the “Class 3” test levels defined in the generic or product-specific standard that references IEC 61000-4-11. Without knowing the product category, you don’t know the exact levels.
Example 2: Explicit level claim
“Voltage dips: 0% U_T for 0.5 cycle, Criterion A; 40% U_T for 10 cycles, Criterion A; 70% U_T for 25 cycles, Criterion A; 0% U_T for 250 cycles, Criterion B”
What it means: Specific, testable performance. The equipment maintains full functionality through 40% dips for 10 cycles and 70% dips for 25 cycles. It may reset during a 5-second complete interruption but recovers automatically.
This is the claim you want to see — it gives you concrete performance data you can plan around.
Example 3: Reference to product standard
“EMC: IEC 60255-26 / IEC 61000-6-5”
What it means: The equipment meets the combined requirements of the product standard (IEC 60255-26 for protection relays) and the generic environment standard (IEC 61000-6-5 for power stations). These product and generic standards internally reference IEC 61000-4-11 and IEC 61000-4-29 for specific test methods — but the actual test levels come from the product/generic standards.
The trust-but-verify approach
When specifying critical equipment, ask the manufacturer for:
- The test report — actual recorded test data, not a summary claim
- The test levels used — specific voltage levels and durations
- The performance criteria achieved — A, B, or C at each test point
- The accredited test laboratory — confirmation that testing was independent, not in-house
A manufacturer confident in their product’s EMC performance will provide all of this. Hesitation is a signal.
Real-World Relevance for Protection Relays
IEC 61000-4-11 and IEC 61000-4-29 are referenced extensively in protection relay standards. Here’s how they apply:
IEC 60255-26 (EMC for protection relays)
This is the protection-relay-specific EMC standard. It references IEC 61000-4-11 for AC aux supply immunity and IEC 61000-4-29 for DC aux supply immunity, with specific test levels and performance criteria appropriate to protection relays.
For a protection relay operating from 220V DC station battery:
- Voltage dips per IEC 61000-4-29: 40% for 100 ms → Criterion A; 70% for 1 s → Criterion A
- Short interruptions per IEC 61000-4-29: 0% for 30 ms → Criterion A; 0% for 5 s → Criterion B
- Voltage variations per IEC 61000-4-29: 80% to 120% for 1 s → Criterion A
What “Criterion A through a 30 ms interruption” means
The relay must continue to function correctly even when its aux supply drops to zero for 30 ms (almost 2 cycles at 50 Hz). This requires:
- Internal energy storage (capacitors on the DC bus, typically sized for 50+ ms holdup)
- Power supply design that prevents output collapse during brief input loss
- Firmware that handles the interruption without resetting
Modern numerical relays are designed specifically to meet this requirement. Older electromechanical or early static relays often cannot — which is one of the reasons substation modernization includes aux supply ride-through improvements.
The ride-through duration matters for fault coordination
Consider a 220V DC substation where a feeder breaker trip causes a brief voltage dip on the aux supply bus. If the upstream relay protecting the transformer meets only Criterion B for the dip duration, it may momentarily reset — creating a window where the transformer is unprotected.
For Category A protection (main transformer, bus differential, etc.), specifying relays that achieve Criterion A through the expected aux supply disturbances is essential. This is why protection engineers scrutinize EMC test reports, not just compliance claims.
Common Confusion Points
“Class 3” vs “Level 3” vs “Category III” — Three similar-sounding terms for different things.
- Test level refers to the severity of the disturbance applied (voltage percentage and duration)
- Installation class (in IEC 61000-4-11) refers to the EMC environment where equipment is installed (Class 1 = protected, Class 4 = severe industrial)
- Overvoltage Category III (from IEC 60255-5) refers to the voltage stress environment the equipment is designed for
Don’t interchange these terms.
“The equipment is IEC 61000-4-11 compliant” (as a standalone claim) — Not useful without specifying which levels and criteria. IEC 61000-4-11 is a test method, not a pass/fail standard. Compliance means “tested per this method” but the outcome is determined by the product or generic standard that references it.
Thinking EMC testing replaces aux supply testing — It doesn’t. EMC tests are type tests performed in a laboratory on a representative sample. Commissioning and maintenance testing of the installed aux supply (voltage, ripple, continuity) is still required.
Confusing AC ripple testing with voltage dip testing — IEC 61000-4-17 covers AC ripple on DC supply. IEC 61000-4-29 covers voltage dips on DC supply. They’re related but separate tests for different phenomena.
Missing the distinction between IEC 61000-4-11 and IEC 61000-6-x — IEC 61000-4-x is the test method. IEC 61000-6-x (generic EMC standards) and IEC 60255-26 (product standard for relays) specify the actual levels and criteria to apply. Both are needed for full compliance.
FAQ
What’s the difference between IEC 61000-4-11 and IEC 61000-4-29?
IEC 61000-4-11 is for AC power inputs (50/60 Hz, up to 16 A per phase). IEC 61000-4-29 is for DC power inputs (up to 360 V DC, up to 25 A). The test philosophy is the same — applying voltage dips, short interruptions, and variations — but the test generator requirements and some specific test parameters differ.
Does IEC 61000-4-29 cover battery charger ripple?
No. Ripple on DC supplies (AC superimposed on the DC waveform) is covered by IEC 61000-4-17. Keep these two standards separate: IEC 61000-4-29 tests sudden voltage changes on DC; IEC 61000-4-17 tests continuous AC ripple on DC.
My equipment’s datasheet says “EMC per IEC 60255-26”. Does that include voltage dips?
Yes. IEC 60255-26 is the product-specific EMC standard for measuring relays and protection equipment. It references IEC 61000-4-11 (for AC aux supplies) and IEC 61000-4-29 (for DC aux supplies) with specific test levels and criteria appropriate to protection relays. Full IEC 60255-26 compliance includes voltage dip testing.
What’s the practical difference between a 16.7 ms dip and a 20 ms dip?
None practically — they’re the same duration expressed for 60 Hz (1 cycle = 16.7 ms) and 50 Hz (1 cycle = 20 ms). IEC 61000-4-11 test tables typically list both with the “10/12 cycles” notation, meaning 10 cycles at 50 Hz or 12 cycles at 60 Hz — either gives 200 ms.
Can I do these EMC tests in the field?
Generally no. Both standards require controlled test conditions, calibrated test generators, and specific instrumentation. Field testing of voltage dip immunity requires specialized equipment (like the Omicron CMC or Megger SMRT test sets with EMC modules) and is typically done only for troubleshooting or verifying specific claims — not for formal type certification.
What happens if my equipment fails the EMC test?
Depends on how it fails. A failure that shows only Criterion C (requires operator reset) might be acceptable for some applications. A failure at Criterion D (hardware damage, data loss) is generally a design defect requiring hardware or firmware changes. The manufacturer typically improves the design and retests.
Are these standards current? I’ve seen references to IEC 61000-4-11 from 2004.
Yes, the current edition of IEC 61000-4-11 is the 2004 edition with Amendment 1 from 2017 (referenced as IEC 61000-4-11:2004+AMD1:2017). The 2004 edition is the most recent full edition — it was updated by amendment rather than reissued as a new edition. IEC 61000-4-29 remains at its 2000 edition, still current.
Key Takeaways
- IEC 61000-4-11 is the primary standard for voltage dip, short interruption, and voltage variation immunity on AC supplies (50/60 Hz, up to 16 A).
- IEC 61000-4-29 is the companion standard for DC supplies (up to 360 V, up to 25 A), covering station batteries, telecom −48V, industrial DC, and UPS buses.
- Both are basic EMC publications — they define test methods. Specific test levels come from product standards (IEC 60255-26, IEC 60601, etc.) or generic standards (IEC 61000-6-x).
- Four performance criteria: A (no effect), B (temporary, auto-recovery), C (temporary, operator reset), D (permanent damage). Product standards specify which criterion applies at each test severity.
- Test level notation: “40% U_T” means voltage drops TO 40% of rated (not BY 40%). A 40% dip on 230 V = 92 V residual.
- IEC 61000-4-29 tests both source impedance conditions — high impedance (source switching) and low impedance (fault clearing). This is unique to DC testing.
- On a datasheet, look for specific claims: level × duration × criterion. Vague “IEC 61000-4-11 compliant” claims aren’t enough for critical equipment.
- For protection relays: Criterion A through voltage dips means the relay continues to protect during the disturbance. Criterion B means momentary reset — which may leave the system unprotected briefly.
Standards Referenced in This Article
| Standard | Key Content |
|---|---|
| IEC 61000-4-11:2004+AMD1:2017 | Voltage dips, short interruptions, variations on AC input ports |
| IEC 61000-4-29:2000 | Voltage dips, short interruptions, variations on DC input ports |
| IEC 61000-4-17 | AC ripple on DC input port immunity (separate from 4-29) |
| IEC 61000-6-5 | Generic EMC standard for power station environments |
| IEC 60255-26 | EMC requirements for measuring relays and protection equipment |
| IEC 60255-1:2022 | Common requirements for protection relays — references aux supply tests |
| IEC Guide 107 | Framework for basic EMC publications |