What is the difference between IEC 61000-3-2 and IEC 61000-3-3?

Both standards regulate the disturbance a product sends back to the AC mains, but they measure different quantities. IEC 61000-3-2 measures the harmonic currents that the product draws, that is the spectral components of the input current at integer multiples of 50 Hz, from order 2 up to order 40. IEC 61000-3-3 measures the voltage fluctuations that result at a reference network impedance, and their flicker effect on incandescent lighting. One quantifies the injected current, the other the voltage seen by the neighbours. Both apply to equipment with a rated input current less than or equal to 16 A per phase. Above that, the companion standards are IEC 61000-3-12 for harmonics and IEC 61000-3-11 for fluctuations.

Which product falls into which IEC 61000-3-2 class?

IEC 61000-3-2 defines four equipment classes. Class A is the default: balanced three-phase equipment, household appliances, non-portable tools, and any product that does not fall into another class. Class B covers portable tools as defined in the standard. Class C covers lighting equipment, with an additional sub-categorisation introduced for low-power LED luminaires. Class D covers equipment with active input power above 75 W and up to 600 W that presents the special current waveform defined by the standard, typically personal computers and television sets with a switched-mode power supply. The declared class is a documented decision in the technical file, and a product placed in the wrong class fails market surveillance.

What do Pst and Plt actually measure?

Pst (short-term flicker indicator) is the short-term flicker indicator. It is computed over a ten-minute window by weighted integration of the voltage fluctuations through the standardised eye-and-incandescent-lamp model (the flicker meter described in IEC 61000-4-15). The limit set by IEC 61000-3-3 is Pst less than or equal to 1.0. Plt (long-term flicker indicator) is the long-term indicator, computed over two hours by cubic summation of twelve consecutive Pst values. The limit is Plt less than or equal to 0.65. Both limits apply simultaneously: a product that meets Pst but exceeds Plt fails the test. The values come directly from table 1 of IEC 61000-3-3.

What are dc and Tmax in IEC 61000-3-3?

Pst and Plt are statistical indicators of the cumulative perception of flicker. Dc (relative voltage change) and Tmax are deterministic bounds on individual voltage events. Dc is the relative difference between the voltage before and after a change, expressed as a percentage of the nominal voltage. The standard requires dc less than or equal to 3.3 per cent in steady state and less than or equal to 4 per cent for momentary variations. Tmax is the duration during which dc remains above 3.3 per cent: the limit is 500 ms. A product whose rectifier with large bulk capacitance produces an inrush peak at power-on can exceed the 4 per cent dc bound or the Tmax bound without necessarily failing Pst or Plt. The four limits are independent.

How does a switched-mode converter with PFC affect compliance?

A switched-mode power supply without power factor correction (PFC) draws current from the mains in narrow pulses at the top of the sine wave, producing a harmonic spectrum dominated by odd orders 3, 5, 7, 9 and beyond. A product above 75 W in this configuration typically exceeds class D limits without difficulty. Active PFC forces the input current to follow the sinusoidal shape of the voltage, bringing the harmonics back below class A or C limits as applicable. On the flicker side, active PFC also reduces the inrush current at power-on, lowering the momentary voltage changes seen by the network. That is why mains-powered products above about 75 W almost always include active PFC, and often a dedicated soft-start stage to limit Tmax.

What hardware is needed for the test setup?

Three items: a reference network impedance Zref compliant with IEC 60725, a power analyser compliant with IEC 61000-4-7 for the harmonic measurement, and a flicker meter compliant with IEC 61000-4-15 for the Pst and Plt computation. The product is powered through the reference impedance, which simulates a typical low-voltage network connection point. The current and voltage probes of the power analyser sample the quantities at the product interface, and the flicker meter integrates the voltage variations through the standardised lamp-and-eye model. Accredited labs use integrated chains, typically from suppliers such as EM Test, Schaffner or California Instruments. A pre-compliance measurement without a reference Zref can under-estimate flicker severity by several dB.

How does the class C sub-categorisation for LED lighting work?

Originally, class C of IEC 61000-3-2 set harmonic limits expressed as a percentage of the fundamental current, tuned for the magnetic and electronic ballasts of fluorescent sources. With the generalisation of low-power-factor LED sources, the standard was revised to introduce a sub-categorisation: LED luminaires with active input power above 25 W fall under the class C limits for "input power greater than 25 W", while those with active input power up to and including 25 W fall under an adapted set of limits that bound the percentage of order 3, the phase angle of the current onset, and the power factor. The aim is to prevent consumer LED luminaires from saturating low-voltage distribution networks with third-harmonic content despite their low individual power.

What are the recurring pitfalls in harmonic and flicker pre-compliance?

Four pitfalls keep showing up in first-pass reports. First, incorrect class declaration: a product declared class A that should have been class D fails the order 3 and order 5 limits with no recourse. Second, missing PFC: above about 75 W, the absence of a correction stage is almost always disqualifying. Third, neutral current asymmetry on three-phase: some asymmetric three-phase products (distributed battery chargers, commercial lighting on multiple phases) generate a large neutral current at order 3 that sums arithmetically across phases instead of cancelling vectorially. Fourth, the confusion between pre-compliance on a lab outlet and compliance with a reference Zref: a measurement on a real lab mains can under-estimate flicker significantly, because the impedance of a typical lab socket is lower than the reference Zref and masks the effect.

Harmonics and flicker (IEC 61000-3-2 and 3-3): mains quality

Author Hugues Orgitello Last updated 27 May 2026 ~13 min read

Guide - Mains quality

IEC 61000-3-2 and IEC 61000-3-3 regulate the disturbance a product injects back into the AC supply network. The first measures the harmonic currents drawn at integer multiples of 50 Hz and sets per-class limits. The second measures the voltage fluctuations these cause at the point of common coupling, expressed as flicker indicators Pst and Plt, and as deterministic bounds dc and Tmax on individual events. Both apply to equipment with a rated input current of 16 A or less per phase and are harmonised under Directive 2014/30/EU (EMC). Above 16 A, IEC 61000-3-12 takes over for harmonics and IEC 61000-3-11 for fluctuations. This page covers the 3-2 classification, the 3-3 limits, the reference network test setup, and the recurring declaration and design pitfalls.

What the two standards regulate

The AC supply network is not a passive sink: every product attached to it locally distorts the current and the voltage. A switched-mode power supply without power factor correction draws current in narrow pulses at the top of the sine wave, producing a rich harmonic spectrum. A motor-driven compressor, a battery charger or a thermostatically controlled heater causes abrupt voltage changes at every start, perceived as flicker of incandescent lighting. Aggregated over many users sharing the same feeder, these disturbances degrade the quality of the distributed voltage.

The European EMC directive 2014/30/EU requires every product intended for connection to the public mains to limit the disturbance it injects. IEC 61000-3-2 and IEC 61000-3-3, in their harmonised forms EN 61000-3-2 and EN 61000-3-3, provide the technical rules for equipment up to 16 A per phase, which covers almost all household, lighting, consumer and light professional electronics. Beyond that, IEC 61000-3-12 and IEC 61000-3-11 apply with rules adapted to higher-current installations.

Split of scope between 3-2, 3-12, 3-3, 3-11

Measured phenomenon	Rated current up to 16 A per phase	Rated current above 16 A per phase
Harmonic current	IEC 61000-3-2	IEC 61000-3-12 (16 A to 75 A)
Voltage fluctuations and flicker	IEC 61000-3-3	IEC 61000-3-11 (16 A to 75 A)

Above 75 A per phase, evaluation is by installation study on a case-by-case basis under IEC 61000-3-14 or by agreement with the local network operator. For a consumer or light commercial product, the 3-2 plus 3-3 pair covers the bulk of the EMC mains file.

IEC 61000-3-2: harmonic current

Principle

A pure 50 Hz sinusoidal current drawn by the product generates no harmonics. Any departure from the sine, whether from a capacitor-input rectifier, a phase-controlled thyristor drive, a switched-mode power supply, an electronic ballast or a variable-speed motor drive, translates into spectral components at integer multiples of 50 Hz: 100 Hz, 150 Hz, 200 Hz, and so on up to 2000 Hz for order 40.

IEC 61000-3-2 limits the amplitude of each of these components, order by order, from 2 to 40. The limits are expressed either in absolute amperes (classes A and B) or as a percentage of the fundamental current (classes C and D), with different relations by class.

The four equipment classes

The classification is defined in clause 5 of the standard. The table below gives the conceptual reading, without reproducing the numerical limits of annex A.

Class	Definition	Typical examples	Type of limits
A	Default equipment: balanced three-phase, household appliances, non-portable tools, anything not in another class	Refrigerator, washing machine, office equipment except PCs, lighting outside class C	Absolute amperes, orders 2 to 40
B	Portable tools as defined by the standard	Portable drill, sander, jigsaw	Limits = 1.5 times class A, orders 2 to 40
C	Lighting equipment, with LED sub-category for active power up to 25 W	Fluorescent luminaire, LED luminaire, discharge lamp	Percentage of fundamental, with bounds on order 3 and on power factor
D	Equipment with active power 75 W up to 600 W presenting the special current waveform defined by the standard	Desktop PC, television, monitor with switched-mode supply and no PFC	Percentage of fundamental, plus an ampere-per-watt cap

The declared class is documented in the test report. A wrong declaration is one of the top causes of market surveillance failure in Europe. General rule: if the product falls into several classes, the most restrictive class applies.

Special waveform (class D)

Class D does not apply to every product between 75 W and 600 W. It applies only to equipment whose input current waveform fits a specific envelope defined by the standard: zero current over a significant fraction of the period, narrow peaks at the top of the sine wave. That is the signature of a switched-mode supply without PFC, or of a single-phase capacitor-input rectifier. The verification of class D membership is performed during a dedicated test, by overlaying the input current on the envelope. A product that falls outside the envelope stays in class A.

Class C sub-categorisation for LED lighting

Mass-market LED lighting, typically at low power (up to 25 W), triggered the revision of class C in recent editions of IEC 61000-3-2. The low-power LED sub-category applies an adapted set of limits that specifically bound the order 3 percentage, the phase angle at which the current starts, and the power factor, rather than imposing the original full table. Without this adaptation, mass-market LED luminaires would saturate the low-voltage distribution neutral with third-harmonic content.

Limits by order: principle (without reproducing annex A)

Annex A of IEC 61000-3-2 gives the numerical limits by order, in amperes or percent depending on the class. Three general properties stand out.

Odd orders (3, 5, 7, 9, 11, 13, 15 and so on) are systematically more restrictive than even orders. The physical reason is the symmetry of typical load waveforms: a single-phase symmetric rectifier load only produces odd orders.
The limits decrease as the order increases, roughly as 1/n. Order 3 has the highest limit, order 39 the lowest.
Even orders above 2 are constrained mainly for asymmetric loads (half-wave rectifiers, asymmetric phase-controlled drives). In practice, full-wave rectifier products produce little even-order content.

For the numerical detail order by order, refer directly to annex A of the standard in the edition in force.

Measurement: power analyser and IEC 61000-4-7

The harmonic measurement is performed with a power analyser compliant with IEC 61000-4-7, which specifies the discrete Fourier transform procedure on a 200 ms sliding window (10 cycles at 50 Hz, or 12 cycles at 60 Hz). The grouping of adjacent harmonics is defined there, as well as the treatment of interharmonic components for transient-regime loads. The manufacturer provides to the lab a report stating the observation duration, the load stability during the test, and the operating mode of the product during the measurement (rated load or representative cycle). See CE testing for how this test fits into the full qualification sequence.

IEC 61000-3-3: voltage fluctuations and flicker

Principle

Flicker is the visual perception of incandescent lighting variation caused by voltage fluctuations. The physiological effect was characterised in the 1960s by accumulation of low-frequency voltage variations (below 35 Hz, with a sensitivity peak around 8.8 Hz) applied to a 60 W incandescent lamp at 230 V. The standardised flicker meter (IEC 61000-4-15) implements the resulting eye-and-incandescence filter model: it integrates the voltage variation through this model to produce a perceived severity indicator.

IEC 61000-3-3 directly bounds that indicator, and separately bounds the individual voltage changes produced by the product in steady state and at power-on.

Limits of IEC 61000-3-3

The four bounds come from table 1 of the standard (in force edition 2013+A1+A2).

Indicator	Definition	Limit	Source
Pst	Short-term flicker indicator, computed over 10 minutes	less than or equal to 1.0	IEC 61000-3-3 clause 5.2
Plt	Long-term flicker indicator, computed over 2 hours (cubic summation of 12 Pst values)	less than or equal to 0.65	IEC 61000-3-3 clause 5.2
dc	Relative voltage change in steady state	less than or equal to 3.3 per cent (steady state), less than or equal to 4 per cent (momentary variation)	IEC 61000-3-3 clause 5.2
Tmax	Duration during which dc remains above 3.3 per cent	less than or equal to 500 ms	IEC 61000-3-3 clause 5.2

The four bounds apply simultaneously. A product that meets Pst and Plt but exceeds dc or Tmax fails. The logic of the two families is complementary: Pst and Plt accumulate perception over long durations (10 min then 2 h), dc and Tmax cap each event individually.

Reference impedance Zref under IEC 60725

The measurement cannot be performed on an arbitrary lab mains: the impedance of the distribution network directly affects the voltage variation produced by a given current. IEC 61000-3-3 requires a reference impedance Zref defined by IEC 60725, representative of a typical low-voltage public network point of common coupling.

For a 230 V single-phase 50 Hz network, Zref is: 0.4 ohms resistive and 0.25 ohms (at 50 Hz, that is about 0.8 mH) inductive. This value corresponds to a typical domestic connection with a representative cable length from the distribution transformer. The test bench inserts this impedance between the stabilised mains source and the equipment under test. The flicker meter and the power analyser measure the quantities between the impedance and the product.

A measurement on a direct lab outlet (without Zref) systematically under-estimates flicker severity, because the actual impedance of a lab socket is typically two to five times lower than Zref. An informative pre-compliance measurement must take this into account.

Representative duty cycle

Pst is computed over a 10-minute window during which the product must operate in a mode representative of real use. For a refrigerator, that is the compressor on-off cycle. For a hair dryer, a typical start-stop cycle. For a PC, a mixed office mode with disk activity and processor cycles. The test report documents the exact cycle used. An artificially smoothed cycle does not represent actual use and is not in the spirit of the standard.

3-2 + 3-3 in the CE technical file

The two standards are harmonised under Directive 2014/30/EU (EMC). For a mains-powered product on the public network, the full EMC evaluation typically covers generic emissions and immunity (CISPR 32, IEC 61000-4-x) plus the 3-2 plus 3-3 pair for mains quality.

When each standard applies

IEC 61000-3-2 applies to any equipment powered by low-voltage AC connected to the public network, with a rated input current up to 16 A per phase. Household appliances, lighting, consumer electronics, office electronics, servers and energy systems below 16 A per phase fall in its scope.
IEC 61000-3-3 applies to the same equipment perimeter with an additional criterion of likelihood to cause flicker. Clause 6.2 of the standard provides exemption conditions for products whose maximum current variation is very low or which present no perceptible cyclic variation (supplies in permanent stable mode). A static IT product without a perceptible cycle can be exempt from 3-3 on documented evidence. The test report records the rationale.

Typical content in the technical file

The EMC technical file of a mains product typically contains:

The IEC 61000-3-2 test report (or documented exemption rationale for products under 75 W outside lighting).
The IEC 61000-3-3 test report (or documented exemption rationale under clause 6.2).
The declared classification (A, B, C, or D) with its justification.
The operating mode used during the test (rated load, representative cycle).
The bench schematic with Zref.

See RED testing for the specific case of radio products on the mains (3-2 plus 3-3 come on top of article 3.2 radio tests).

Typical architecture of a compliant mains product

Rectifier and PFC stage

The canonical architecture of a mains supply compliant with both standards above about 75 W is:

   AC mains           Conducted        Rectifier      Active PFC      High-       DC-DC          Application
   230 V 50 Hz   -->  EMC filter   --> bridge      --> stage      -->  voltage --> downstream --> load
                                                                       DC bus       converter

The active PFC stage forces the input current to a sinusoidal shape in phase with the voltage, bringing orders 3, 5, 7, 9 below the class A or D limits as applicable. Typical PFC controllers (NCP1654, UCC28180, L4984D) operate in continuous or critical boost mode, with a switching frequency of 60 to 150 kHz that does not affect mains compliance but must be filtered for conducted emissions.

Soft-start and Tmax containment

At power-on, the bulk DC capacitor charges through the rectifier bridge. Without limiting, the inrush current can reach several tens of amperes during a few milliseconds, producing a momentary voltage drop above the 4 per cent dc limit and a Tmax above 500 ms. The standard countermeasure is an NTC thermistor in series on the input line, or a soft-start MOSFET active during the initial charge phase and short-circuited by a relay or thyristor in steady state.

Below 75 W

Below about 75 W of active power, IEC 61000-3-2 provides exemptions or relaxed limits depending on the class. A 30 W switched-mode supply for an IoT gateway typically does not need PFC to meet the limits of the applicable class. For LED lighting, the low-power class C sub-category still imposes a bound on order 3 and on the power factor.

Recurring pitfalls

Four pitfalls account for most first-pass failures.

Wrong class declaration. A product declared class A but matching the class D envelope fails the order 3 and order 5 limits. The verification of class D membership is done by overlaying the input current waveform on the envelope defined by the standard. It is a preliminary measurement that should be made systematically before the full-table test.
No PFC above 75 W. The canonical switched-mode supply without PFC produces a dominant spectrum at orders 3, 5, 7 that is incompatible with the limits above about 75 W. The countermeasure is an active boost PFC controller. A passive PFC (input series inductor) is not enough in practice above 100 W.
Neutral asymmetry on three-phase. An asymmetric three-phase product (multi-outlet charger, commercial lighting across phases) produces a large neutral current at order 3 that sums arithmetically across phases instead of cancelling vectorially, because third harmonics are in phase across the three conductors. The neutral sees the sum of the three order 3 currents. The countermeasure is to balance the load or to size up the neutral.
Pre-compliance without Zref. Measuring Pst on a direct lab mains, whose impedance is typically two to five times lower than Zref, yields an under-estimated Pst that hides a real overshoot. A useful pre-compliance setup uses a reference impedance network, either dedicated (Schaffner NSG 1007, EM Test NETWORK 3) or built from a calibrated inductor and resistor box. See CE pitfalls for the documentation pitfalls on the file side.

Key takeaways

IEC 61000-3-2 measures the harmonic content of the input current drawn by the product, orders 2 to 40, with four equipment classes (A default, B portable tools, C lighting with low-power LED sub-category, D PCs and TVs from 75 to 600 W with special waveform).
IEC 61000-3-3 measures the voltage changes the product produces at the point of common coupling, expressed as Pst (limit 1.0 over 10 min), Plt (limit 0.65 over 2 h), dc (limit 3.3 per cent in steady state, 4 per cent momentary), Tmax (limit 500 ms).
Both standards apply to equipment with a rated input current of 16 A or less per phase. Above that, IEC 61000-3-12 and IEC 61000-3-11 take over up to 75 A.
The test bench requires a reference impedance Zref defined in IEC 60725, a power analyser compliant with IEC 61000-4-7, and a flicker meter compliant with IEC 61000-4-15.
Active PFC is the canonical countermeasure for products above 75 W. Soft-start is the canonical countermeasure for Tmax containment at power-on.
The recurring pitfalls are wrong class declaration, missing PFC, three-phase neutral asymmetry, and pre-compliance without Zref.

For the definitions of terms used here, see the Glossary. For the conducted emissions measurement associated with the mains filter, see conducted emissions at the LISN. For how 3-2 plus 3-3 fit in the qualification sequence, see CE testing.

Harmonics and flicker (IEC 61000-3-2 and 3-3): mains quality

What the two standards regulate

Split of scope between 3-2, 3-12, 3-3, 3-11

IEC 61000-3-2: harmonic current

Principle

The four equipment classes

Special waveform (class D)

Class C sub-categorisation for LED lighting

Limits by order: principle (without reproducing annex A)

Measurement: power analyser and IEC 61000-4-7

IEC 61000-3-3: voltage fluctuations and flicker

Principle

Limits of IEC 61000-3-3

Reference impedance Zref under IEC 60725

Representative duty cycle

3-2 + 3-3 in the CE technical file

When each standard applies

Typical content in the technical file

Typical architecture of a compliant mains product

Rectifier and PFC stage

Soft-start and Tmax containment

Below 75 W

Recurring pitfalls

Key takeaways

See also