Conducted emissions: LISN method, CISPR and FCC limits
Conducted emissions are the radio-frequency voltage a product pushes back onto its power lead. The European and US regimes both limit it from 150 kHz to 30 MHz, measured through a LISN (Line Impedance Stabilisation Network, which CISPR calls a V-network artificial mains network). This page goes back to the texts: which network CISPR 16-1-2 actually specifies for which band, the CISPR 32 and 47 CFR 15.107 limit tables side by side, what the FCC detector rule allows, which EN 55032 version the EU list cites in October 2026, and the common readings the texts contradict. It is written for product engineers preparing an EMC campaign and for project managers who need to know why a bench result is not a lab result.
What conducted emissions measure
Section titled “What conducted emissions measure”The FCC rule gives the cleanest definition of the quantity: compliance "shall be based on the measurement of the radio frequency voltage between each power line and ground at the power terminal" (47 CFR 15.107(a)), on any frequency in the band 150 kHz to 30 MHz, measured with a 50 μH/50 ohm LISN. CISPR 32 sets its AC mains port limits over the same band and in the same unit, dB(μV).
Why 150 kHz? The FCC explained it when it moved its own limits down from 450 kHz to 150 kHz in 2002: the change brought harmonisation with CISPR 22 and protects licensed services below 450 kHz, the Report and Order citing Differential GPS beacons between 285 and 325 kHz used for safety-of-life navigation. Why 30 MHz? The same order states that the conducted limits "protect against interference to licensed radio services operating below 30 MHz"; above that, radiated emission limits take over.
Common mode and differential mode
Section titled “Common mode and differential mode”On a two-wire lead, two propagation modes coexist.
- Differential mode (DM): current flows out on one conductor and back on the other, like the power current itself. Switching current pulses in the input stage of a converter are a typical DM source.
- Common mode (CM): current flows in the same direction on both conductors and returns to the reference ground through stray capacitance. It depends on the layout, the heat sinks and the distance to ground, which makes it the harder mode to predict.
The network measures each line to ground, so the receiver sees a combination of both modes. The distinction matters for the fix: a capacitor between line and neutral acts on DM only, a capacitor from each line to earth and a common-mode choke act on CM.
The artificial mains network in CISPR 16-1-2
Section titled “The artificial mains network in CISPR 16-1-2”The current edition is CISPR 16-1-2:2014 (edition 2.0, March 21, 2014) with Amendment 1 of November 7, 2017, sold as the consolidated edition 2.1. The IEC online store shows no new edition under development for this part. Clause 4.1 sets the three functions of an LISN: provide a defined impedance at radio frequencies at the EUT terminals, isolate the test circuit from unwanted signals on the supply mains, and couple the disturbance voltage to the measuring receiver. Clause 3 adds that "the terms line impedance stabilization network (LISN) and V-AMN are used interchangeably".
Which network for which band
Section titled “Which network for which band”| Clause | Network | Frequency range | Typical use |
|---|---|---|---|
| 4.3 | 50 Ω/50 μH + 5 Ω V-AMN | 9 kHz to 150 kHz | Products with limits below 150 kHz (for example induction cooking) |
| 4.4 | 50 Ω/50 μH V-AMN | 150 kHz to 30 MHz | The reference network for CISPR 32 and FCC Part 15 mains measurements |
| 4.5 | 50 Ω/5 μH + 1 Ω V-AMN | 150 kHz to 108 MHz | Low-impedance supplies, for example vehicle and high-current set-ups |
| 4.6 | 150 Ω V-AMN | 150 kHz to 30 MHz | Product standards that call for 150 Ω |
| 4.7 | 150 Ω delta-network (Δ-AMN) | 150 kHz to 30 MHz | Measures symmetric and asymmetric voltages separately |
Source: CISPR 16-1-2:2014, table of contents and clause 4. The "typical use" column is ours; the product standard decides which network applies.
A note under clause 4.3 adds that a network meeting the combined impedance requirements of 4.3 and 4.4 can also be used from 150 kHz to 30 MHz, which is why many commercial LISN models are sold as "50 Ω/50 μH + 5 Ω, 9 kHz to 30 MHz". The 50 Ω/50 μH + 5 Ω characteristic itself is specified only up to 150 kHz.
What the impedance requirement says
Section titled “What the impedance requirement says”- Impedance is specified in magnitude and phase, measured at an EUT terminal against the reference ground with the receiver port terminated in 50 Ω (clause 4.2).
- It must hold "for any value of external impedance, including a short circuit" at the mains terminal, at all temperatures the network reaches, for continuous currents up to the rated maximum and for peak currents up to the specified maximum (clause 4.2). A network driven past its peak-current rating by inrush or by a capacitor-input rectifier no longer gives a valid measurement.
- A 10 dB attenuator (internal or external, VSWR at most 1.2 to 1) ensures the 50 Ω termination of the receiver port, and its loss is part of the voltage division factor (clauses 4.2 and 4.11). An unused output must be terminated in 50 Ω.
- For the 9 kHz to 150 kHz network, Table 1 gives the target curve with tolerances of ±20 % on magnitude and ±11.5° on phase: 5.22 Ω at 9 kHz, 25.11 Ω at 100 kHz, 32.72 Ω at 150 kHz.
The FCC requirement is the same in substance: 47 CFR 15.31(l) requires "a 50 ohm/50 uH line-impedance stabilization network (LISN)" for measurements of emissions conducted to the power lines, and the 2002 Report and Order replaced the 5 μH/50 ohm LISN previously used for some Part 18 equipment by the 50 μH/50 ohm network, citing the CISPR impedance curve.
Set-up
Section titled “Set-up”Measurement methods are in CISPR 16-2-1 (current edition 3.1: the 2014 third edition with Amendment 1 of June 30, 2017, plus Corrigendum 1 of August 31, 2020). It is a basic standard covering conducted disturbance measurements from 9 kHz to 30 MHz. The product standard then fixes the arrangement: for multimedia equipment, CISPR 32 Annex D carries the measurement arrangements (Table D.1) and the spacings, distances and tolerances (Table D.2). In the US, 47 CFR 15.31(a)(4) points to ANSI C63.4-2014, excluding clauses 4.5.3, 4.6, 6.2.13, 8.2.2, 9 and 13. Take the distances from the standard you are reporting against, not from a generic checklist.
AC mains limits: CISPR 32, FCC 15.107, 15.207 and 18.307
Section titled “AC mains limits: CISPR 32, FCC 15.107, 15.207 and 18.307”CISPR 32:2015 carries the AC mains port limits in Annex A: Table A.9 for Class A and Table A.10 for Class B. The FCC adopted the CISPR 22 conducted limits in 2002 (ET Docket 98-80), and CISPR 32 kept those values, so the numbers below are the same in both regimes.
| Band (MHz) | Class A QP | Class A AVG | Class B QP | Class B AVG |
|---|---|---|---|---|
| 0.15 to 0.5 | 79 | 66 | 66 to 56 | 56 to 46 |
| 0.5 to 5 | 73 | 60 | 56 | 46 |
| 5 to 30 | 73 | 60 | 60 | 50 |
Values in dB(μV). Class B limits from 0.15 to 0.5 MHz decrease with the logarithm of the frequency (47 CFR 15.107(a) footnote). Class A: 47 CFR 15.107(b); Class B: 47 CFR 15.107(a).
Written out, the sloped segment is a straight line in log f: QP limit = 66 − 19.1 × log10(f / 0.15 MHz) dB(μV), and AVG = QP − 10 dB, which gives 56 and 46 dB(μV) at 0.5 MHz. (This is our arithmetic from the two end points the tables give.)
The gap between classes, per band and detector
Section titled “The gap between classes, per band and detector”| Point | QP gap (A − B) | AVG gap (A − B) |
|---|---|---|
| 150 kHz | 13 dB | 10 dB |
| Just below 500 kHz | 23 dB | 20 dB |
| 500 kHz to 5 MHz | 17 dB | 14 dB |
| 5 MHz to 30 MHz | 13 dB | 10 dB |
Derived from the table above. A design sized for Class A will generally need a different input filter to reach Class B.
Which FCC section applies
Section titled “Which FCC section applies”| Rule | Equipment | Limits | Notes from the text |
|---|---|---|---|
| 15.107(a) | Class B digital devices (unintentional radiators) | Class B row above | "The lower limit applies at the band edges" |
| 15.107(b) | Class A digital devices | Class A row above | Lower limit applies at the boundary between ranges |
| 15.107(c), 15.207(b) | Carrier current systems below 30 MHz | No limit for systems received on a standard AM broadcast receiver, 1000 μV in 535 to 1705 kHz for all others | Replaces the tables above |
| 15.107(d), 15.207(c) | Battery-only devices | No conducted test | Not exempt if the device can operate while charging, from an AC adapter or through another mains-powered device |
| 15.207(a) | Intentional radiators (transmitters) on the mains | Same values as Class B | Applies to radio products with an AC connection |
| 18.307(a) | Induction cooking ranges, ultrasonic equipment | 110 dB(μV) QP 9 to 50 kHz, 90 to 80 dB(μV) QP 50 to 150 kHz, then Class B values | These limits start at 9 kHz, below the 150 kHz lower edge of the 50 Ω/50 μH network of CISPR 16-1-2 clause 4.4 |
| 18.307(b) | Other Part 18 consumer devices | Same values as Class B | 18.307(d): if the quasi-peak reading meets the average limit, no separate average test is needed |
The transition is long over: 47 CFR 15.37(c) required the 15.107 and 15.207 limits for equipment authorised on or after July 12, 2004, and for all equipment manufactured or imported on or after July 11, 2005.
Wired network ports are a separate table
Section titled “Wired network ports are a separate table”CISPR 32 adds conducted limits that the FCC Part 15 rules do not have: Table A.11 (Class A) and Table A.12 (Class B) for asymmetric mode emissions from wired network ports, and Table A.13 for conducted differential voltage emissions from Class B equipment. Those network-port limits are expressed as voltage and as current, measured with the coupling devices CISPR 16-1-2 specifies (asymmetric artificial networks, current and voltage probes). They are an addition for ports such as Ethernet, not a replacement for the mains-port measurement.
CISPR 11 for industrial, scientific and medical equipment
Section titled “CISPR 11 for industrial, scientific and medical equipment”CISPR 11 covers ISM equipment. The current edition is CISPR 11:2024 (edition 7.0, February 13, 2024); an Amendment 1 is in preparation at IEC. It splits equipment into group 1 and group 2 (group 2 being equipment that intentionally generates radio-frequency energy for the treatment of material, such as induction heating or RF welding) and into Class A and Class B. Its scope reaches 9 kHz to 400 GHz for emissions. The FCC used CISPR 11 as the model for its Part 18 conducted limits in 2002, and 47 CFR 18.307(b) applies the same values as Part 15 Class B to consumer ISM devices. Which product standard applies (CISPR 11, CISPR 32 or another) is decided from the scope of each standard and recorded in the technical file. See CE tests.
In the EU, the cited version is still EN 55011:2016 with A1:2017 and A11:2020, not the European adoption of CISPR 11:2024 (see the status table below).
Detectors: what the texts require
Section titled “Detectors: what the texts require”CISPR 16-1-1:2019 (edition 5.0, May 22, 2019; an amendment is in preparation) specifies one receiver type per detector:
| Detector | CISPR 16-1-1 clause | Frequency range | What it is for |
|---|---|---|---|
| Quasi-peak (QP) | 5 | 9 kHz to 1000 MHz | Weights disturbances by repetition rate (5.2.2) |
| Peak | 6 | 9 kHz to 18 GHz | Fast scans; reads at least as high as QP |
| Average | 7 | 9 kHz to 18 GHz | Steady narrowband lines; includes response to intermittent and drifting disturbances (7.3.3) |
| RMS-average | 8 | 9 kHz to 18 GHz | Used where a product standard calls for it |
CISPR 32 and 47 CFR 15.107 both give a QP limit and an average limit, and the product must meet both. The FCC adds one option in 47 CFR 15.35(a): limits at or below 1000 MHz are "based on measuring equipment employing a CISPR quasi-peak detector function", and "as an alternative to CISPR quasi-peak measurements, the responsible party, at its option, may demonstrate compliance" with a peak detector at the same bandwidth. Since a peak reading is never lower than the QP reading of the same signal, this option can only make the test harder, never easier. The instrumentation specification for the QP detector is ANSI C63.4-2014 clause 4, incorporated by reference in 15.35(a).
A practical consequence: a peak scan that stays under the QP and average limits closes the question; a peak reading above a limit only means the final QP and average measurements are needed at that frequency.
Mitigation with passive components
Section titled “Mitigation with passive components”Most mains-port failures are fixed at the input filter. The components are well known; the values depend on the converter, the layout and the safety constraints, so treat any "typical value" list with caution.
- X capacitors (line to neutral) attenuate differential-mode noise. Their safety classes (X1, X2, X3) are defined in IEC 60384-14 by impulse-voltage category. A discharge path is usually needed so that the capacitor does not leave a charge on the plug pins after disconnection; the safety standard of the product sets the requirement.
- Y capacitors (line to earth, neutral to earth) attenuate common-mode noise. Classes Y1, Y2 and Y4 in IEC 60384-14 differ by insulation and impulse rating. Their value is bounded by the touch current and protective conductor current limits of the product safety standard (IEC 62368-1 for audio/video and ICT equipment, IEC 60335-1 for appliances), so the earth capacitance is the first place where EMC and electrical safety trade against each other. IEC 60950-1 was withdrawn by IEC on March 29, 2024 and no longer applies to new designs.
- Common-mode chokes: two windings on one core, wound so that differential currents cancel in the core and common-mode currents see a high impedance.
- Filtered inlets: IEC 60320 C14 inlets with a built-in filter combine the inlet, often the fuse, and an LC filter in one part.
Pre-compliance vs full compliance
Section titled “Pre-compliance vs full compliance”A pre-compliance measurement runs on a development bench, often with a compact LISN, a small ground plate and a spectrum analyser in peak mode. A full-compliance measurement runs in a lab accredited to ISO/IEC 17025, with an artificial network verified against CISPR 16-1-2, the reference ground plane and arrangement of the product standard, and a receiver meeting CISPR 16-1-1.
The usual sources of disagreement between the two follow directly from the requirements above:
- Ground reference: without the reference ground plane and the spacings of CISPR 32 Annex D, the stray capacitance that carries common-mode current is not the one the lab will see.
- Network impedance: a network that does not meet the magnitude and phase requirement of CISPR 16-1-2 clause 4.2 at the operating current, including peak current, gives a different voltage for the same noise source.
- Detector: a peak-only scan overstates pulsed disturbances against the QP limit and does not show the average reading at all.
- Cable arrangement: length, routing and bundling of the mains and interface cables change the common-mode path.
Pre-compliance is good for finding the frequencies that matter and comparing fixes; it does not replace the report. See CE pitfalls for documentation pitfalls.
Common pitfalls in conducted-emissions campaigns
Section titled “Common pitfalls in conducted-emissions campaigns”- Network past its current rating. CISPR 16-1-2 clause 4.2 requires the impedance to hold for continuous and peak currents up to the rated maximum, and clause 4.9 covers current carrying capacity and series voltage drop. Check both ratings against the product, including inrush and the peak current of a capacitor-input rectifier.
- Wrong network for the band. The 50 Ω/50 μH + 5 Ω characteristic is specified for 9 kHz to 150 kHz; for 150 kHz to 30 MHz the reference is the 50 Ω/50 μH network. A network sold for 9 kHz to 30 MHz should state that it meets both.
- Second output left open. The output not connected to the receiver must be terminated in 50 Ω, otherwise the impedance seen by the EUT on that line is not the specified one (clause 4.2).
- Undocumented arrangement. If the cable layout, the position on the ground plane and the operating mode are not recorded, the result cannot be repeated; CISPR 32 Annex D and its test report summary (Table F.1) exist for that reason.
- Battery product assumed exempt. Under 47 CFR 15.107(d), a device that can operate while charging or from an AC adapter must be tested for conducted emissions.
See FCC pitfalls for the US-specific pitfalls.
Status of the texts, October 2026
Section titled “Status of the texts, October 2026”| Text | Status | Date |
|---|---|---|
| CISPR 32 edition 1.0 | Replaced | January 30, 2012 |
| CISPR 32:2015 edition 2.0 | In force at IEC | March 31, 2015 |
| CISPR 32:2015/AMD1:2019 (consolidated edition 2.1) | In force at IEC | October 1, 2019 |
| CISPR 32 edition 3.0 | Draft at CCDV stage, IEC forecast publication January 2027 | Not published |
| EN 55032:2015 + A11:2020 | Cited under Directive 2014/30/EU (Decision (EU) 2020/1630, OJ L 366, November 4, 2020) | Current |
| EN 55032:2012 + AC:2013 | Presumption of conformity withdrawn | May 4, 2022 |
| EN 55011:2016 + A1:2017 + A11:2020 | Cited under Directive 2014/30/EU (Decision (EU) 2020/1630) | Current |
| EN 55011:2009 + A1:2010 | Presumption of conformity withdrawn | May 4, 2022 |
| CISPR 11:2024 edition 7.0 | In force at IEC, Amendment 1 in preparation | February 13, 2024 |
| CISPR 16-1-2:2014 + AMD1:2017 | In force at IEC | November 7, 2017 |
| CISPR 16-2-1:2014 + AMD1:2017, COR1:2020 | In force at IEC | June 30, 2017 / August 31, 2020 |
| CISPR 16-1-1:2019 edition 5.0 | In force at IEC, amendment in preparation | May 22, 2019 |
| FCC conducted limits (FCC 02-157) | Adopted May 23, 2002, effective August 9, 2002 | Mandatory for new authorisations from July 12, 2004 |
| ANSI C63.4-2014 | Referenced in 47 CFR 15.31(a)(4) and 15.35(a) | ANSI approved June 13, 2014 |
The last amendment to Implementing Decision (EU) 2019/1326 is Decision (EU) 2022/910 of June 9, 2022, and no later EMC harmonised standards decision has been adopted, so the consolidated text of June 10, 2022 is the current EU list. EU dates come from that consolidated text; IEC dates from the IEC online store records.
Claims the texts contradict
Section titled “Claims the texts contradict”| Common claim | What the text says |
|---|---|
| "The LISN is a 50 Ω/50 μH + 5 Ω network for 9 kHz to 30 MHz" (this page said so before October 2026) | CISPR 16-1-2 specifies the 50 Ω/50 μH + 5 Ω V-AMN for 9 kHz to 150 kHz (clause 4.3) and the 50 Ω/50 μH V-AMN for 150 kHz to 30 MHz (clause 4.4). A network meeting both may be used over the whole range. |
| "The high-current industrial network is 50 Ω/50 μH + 1 Ω, rated to several kA" | The 1 Ω network in CISPR 16-1-2 is 50 Ω/5 μH + 1 Ω, for 150 kHz to 108 MHz (clause 4.5). The clause title states no current rating. |
| "The delta-network is for products with no neutral; a T-network is used for telecom lines" | The Δ-AMN is a 150 Ω network that couples symmetric and asymmetric voltages separately (clauses 4.1 and 4.7). Telecom and network ports use asymmetric artificial networks and probes, not an AMN. |
| "CISPR 32 lets you use a current probe instead of the LISN on the mains port" | The mains-port limits (Tables A.9 and A.10) are voltage limits through the AMN. Current limits belong to Tables A.11 and A.12 for wired network ports. |
| "Class B is 13 to 23 dB below Class A" | True for the QP limits only. The average-limit gap is 10 to 20 dB. |
| "150 kHz was chosen because it sits above the long-wave broadcast band" | The FCC lowered its limit from 450 kHz to 150 kHz to harmonise with CISPR 22 and to protect services below 450 kHz, naming DGPS at 285 to 325 kHz (FCC 02-157). |
| "FCC uses peak as a complement to QP and AVG" | 47 CFR 15.35(a) makes peak an optional substitute for QP, at the same bandwidth, at the choice of the responsible party. |
| "The EU cites EN 55032 with Amendment 1" | The cited reference is EN 55032:2015 with A11:2020 (Decision (EU) 2020/1630). CISPR 32 AMD1:2019 is not part of the cited reference. |
| "Battery products never need a conducted test" | 47 CFR 15.107(d) exempts only devices that cannot operate while connected to the AC lines, directly or through an adapter or another device. |
| "IEC 60950-1 sets the leakage limit for Y capacitors" | IEC 60950-1 was withdrawn by IEC on March 29, 2024; the current limits are in the product safety standard such as IEC 62368-1. |
Relation to the other EMC tests
Section titled “Relation to the other EMC tests”Conducted emissions on the mains port are one test among several in an EMC campaign for a mains-powered product: radiated emissions, harmonic current and flicker (IEC 61000-3-2 and IEC 61000-3-3 in the EU), wired network port emissions where applicable, and the immunity tests (in the EU, EN 55035 for multimedia equipment, which calls up tests such as electrostatic discharge, surge and EFT/burst). For radio products, Article 3(1)(b) of the Radio Equipment Directive carries the EMC requirement, on top of the radio tests. See RED tests for the detail and CE vs FCC EMC for the full comparison of the two regimes.
Key takeaways
Section titled “Key takeaways”- 150 kHz to 30 MHz, voltage at the power terminal, through a 50 Ω/50 μH network: the same quantity in CISPR 32 and 47 CFR 15.107.
- CISPR 16-1-2 specifies five networks with their own bands; the 50 Ω/50 μH + 5 Ω characteristic is the 9 kHz to 150 kHz one.
- Same numbers on both sides of the Atlantic: CISPR 32 Tables A.9 and A.10 and 47 CFR 15.107(b) and (a) share the values since the FCC adopted the CISPR 22 limits in 2002.
- QP and average limits both apply; the FCC lets you swap QP for peak, never the reverse.
- EU presumption comes from EN 55032:2015 + A11:2020; CISPR 32 edition 3 is still a draft.
- Network ratings matter: the impedance must hold at the product peak current.
For implementation on the CE side, see CE tests. On the US side, see FCC tests. For term definitions, see the Glossary. The US reference text is 47 CFR Part 15.
Sources & references
- CISPR 16-1-2:2014+AMD1:2017 CSV (edition 2.1), Coupling devices for conducted disturbance measurements, IEC webstore.iec.ch/en/publication/61924
- CISPR 16-1-2:2014 preview (clauses 1 to 4.3, table of contents), via iTeh, IEC (preview hosted by iTeh Standards) cdn.standards.iteh.ai/samples/18695/654ac8b7fc284f7fa805646afb36b3db/CISPR-16-1-2-2014.pdf
- CISPR 16-2-1:2014+AMD1:2017 CSV (edition 3.1), Conducted disturbance measurements, IEC webstore.iec.ch/en/publication/60987
- CISPR 16-1-1:2019 (edition 5.0), Measuring apparatus, IEC webstore.iec.ch/en/publication/60774
- CISPR 32:2015 (edition 2.0), Electromagnetic compatibility of multimedia equipment, emission requirements, IEC webstore.iec.ch/en/publication/22046
- CISPR 32:2015 RLV preview (table of contents, Annex A table list), via iTeh, IEC (preview hosted by iTeh Standards) cdn.standards.iteh.ai/samples/20486/c899a27bb5574bdaa724e48fe2f56fd5/CISPR-32-2015.pdf
- CISPR 11:2024 (edition 7.0), Industrial, scientific and medical equipment, RF disturbance characteristics, IEC webstore.iec.ch/en/publication/66118
- 47 CFR 15.107, Conducted limits (unintentional radiators), eCFR www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-B/section-15.107
- 47 CFR 15.207, Conducted limits (intentional radiators), eCFR www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C/section-15.207
- 47 CFR 15.35, Measurement detector functions and bandwidths, eCFR www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-A/section-15.35
- 47 CFR 15.31, Measurement standards (ANSI C63.4-2014, 50 ohm/50 uH LISN), eCFR www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-A/section-15.31
- 47 CFR 15.37, Transition provisions for compliance with the rules, eCFR www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-A/section-15.37
- 47 CFR 18.307, Conduction limits (ISM equipment), eCFR www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-18/subpart-C/section-18.307
- FCC Report and Order, ET Docket 98-80, FCC 02-157, Conducted Emission Limits (67 FR 45666, July 10, 2002), Federal Register / GovInfo www.govinfo.gov/content/pkg/FR-2002-07-10/html/02-17264.htm
- IEEE/ANSI C63.4-2014, Methods of measurement of radio-noise emissions, 9 kHz to 40 GHz, IEEE standards.ieee.org/ieee/C63.4/5841/
- Commission Implementing Decision (EU) 2019/1326, EMC harmonised standards, consolidated text of June 10, 2022, EUR-Lex eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:02019D1326-20220610
- Directive 2014/30/EU on electromagnetic compatibility, EUR-Lex eur-lex.europa.eu/eli/dir/2014/30/oj
Frequently asked questions
- What is the difference between conducted and radiated emissions?
- Conducted emissions are the radio-frequency voltage a product sends back onto the conductors attached to it, first of all the AC mains lead. 47 CFR 15.107 defines the quantity as the radio frequency voltage between each power line and ground at the power terminal, over 150 kHz to 30 MHz, measured with a 50 μH/50 ohm LISN. Radiated emissions are the field the product and its cables radiate into space, measured with an antenna. The same internal sources (switching converters, clocks, fast edges) usually feed both, but the set-ups, frequency ranges and limits are separate.
- What exactly does the LISN do?
- CISPR 16-1-2 (clause 4.1) gives an artificial mains network three jobs: present a defined radio-frequency impedance at the terminals of the equipment under test, isolate the test circuit from unwanted signals on the supply mains, and couple the disturbance voltage to the measuring receiver. The standard notes that LISN and V-AMN are used interchangeably. For 150 kHz to 30 MHz the network is the 50 ohm/50 μH V-AMN of clause 4.4; the 50 ohm/50 μH + 5 ohm network of clause 4.3 is specified for 9 kHz to 150 kHz.
- What is the difference between CISPR 32 Class A and Class B?
- Class B is for equipment intended for residential environments, Class A for other environments. On the AC mains port the Class B quasi-peak limit sits 13 dB below Class A at 150 kHz, up to 23 dB just below 500 kHz, 17 dB from 500 kHz to 5 MHz and 13 dB from 5 MHz to 30 MHz. The average-limit gap is 3 dB smaller in each band (10, 20, 14 and 10 dB). CISPR 32 Tables A.9 and A.10 carry the values, and 47 CFR 15.107(b) and 15.107(a) use the same numbers.
- Can a current probe replace the LISN for a mains-powered product?
- No. For the AC mains port, CISPR 32 Tables A.9 and A.10 and 47 CFR 15.107 express the limits as a voltage in dB(μV) measured through the artificial mains network. Current limits in dB(μA) appear in CISPR 32 Tables A.11 and A.12, which cover asymmetric mode emissions from wired network ports, not the mains port. A product powered only by batteries has no mains port to test: the FCC rule (15.107(d)) exempts it unless it can operate while charging or from an AC adapter.
- Why does CISPR use quasi-peak and average detectors?
- The quasi-peak detector weights a disturbance by its repetition rate (CISPR 16-1-1 clause 5.2.2 specifies the variation with repetition frequency), so isolated pulses read lower than continuous ones. The average detector catches steady narrowband lines such as converter harmonics. CISPR 32 and 47 CFR 15.107 set a quasi-peak limit and an average limit, and both must be met. 47 CFR 15.35(a) lets the responsible party use a peak detector instead of quasi-peak, at the same bandwidth; peak reads at least as high as quasi-peak, so a pass in peak is a pass in quasi-peak.
- Which EN 55032 version gives presumption of conformity in the EU?
- EN 55032:2015 with EN 55032:2015/A11:2020, listed in Implementing Decision (EU) 2019/1326 as amended by Decision (EU) 2020/1630. EN 55032:2012 lost presumption on 4 May 2022. No EMC harmonised standards decision has amended 2019/1326 since Decision (EU) 2022/910, so the CISPR 32 Amendment 1 of 2019 is not part of the cited reference, and CISPR 32 edition 3 is still a draft at IEC.
- Why can a product that passed pre-compliance fail the final lab?
- Because the bench rarely reproduces the conditions the standard fixes: an artificial network whose impedance meets CISPR 16-1-2 at the product current (including peak current), a reference ground plane with the arrangement and spacings of CISPR 32 Annex D, and a receiver whose quasi-peak and average detectors meet CISPR 16-1-1. A peak-only scan with a cheap network is good for finding problems and comparing fixes, not for predicting the margin in the report.