What is the difference between Group 1 and Group 2 in CISPR 11?

Group 1 covers equipment that uses RF energy internally but does not intentionally generate or use RF electromagnetic energy for material processing or inspection. Examples include power supplies, motor drives, LED lighting, and laboratory instruments. Group 2 covers equipment that intentionally generates or uses RF electromagnetic energy in the ISM bands for material treatment, inspection, or similar purposes. Examples include industrial RF heaters, plasma processing systems, microwave ovens, medical diathermy equipment, and electrosurgical units. Group 2 equipment receives more relaxed emission limits (typically 10 to 20 dB higher) at ISM frequencies because some RF leakage is inherent to their operation.

How do CISPR 11 Class A and Class B limits differ?

Class A limits apply to equipment intended for use in industrial environments (factories, laboratories, commercial facilities) and are approximately 10 dB less restrictive than Class B. Class B limits apply to equipment intended for use in residential environments, domestic dwellings, and establishments directly connected to the low-voltage public supply network. For conducted emissions at 0.15 to 0.5 MHz, Class A limits are 79 dBuV (quasi-peak) while Class B limits are 66 dBuV. For radiated emissions at 30 to 230 MHz, Class A limits are 30 dBuV/m at 30 m while Class B limits are 30 dBuV/m at 10 m (equivalent to approximately 20 dBuV/m at 30 m after distance correction). Equipment sold into the EU consumer market must meet Class B limits.

How does CISPR 11 relate to FCC Part 18 and EN 55011?

CISPR 11 is the international base standard. EN 55011 is the European harmonized version adopted under the EU EMC Directive, with identical technical limits plus EU-specific regulatory requirements (Declaration of Conformity, CE marking). FCC Part 18 is the US counterpart covering ISM equipment, with generally similar but not identical limits. Key differences: FCC Part 18 uses different measurement distances (3 m for consumer, 30 m for industrial), different detector types in some bands, and different frequency ranges. Products sold globally often test to both CISPR 11 and FCC Part 18 simultaneously since CISPR 11 compliance does not automatically satisfy FCC requirements.

EMC Standards & Regulations

CISPR 11

/sis-per ee-lev-uhn/

An international EMC standard defining conducted and radiated emission limits for industrial, scientific, and medical (ISM) equipment from 150 kHz to 18 GHz (extended to 26 GHz in Edition 7). Equipment is classified as Group 1 (incidental RF generation: power supplies, motor drives) or Group 2 (intentional RF use: plasma systems, RF heaters, microwave ovens). Within each group, Class A limits apply to industrial environments while Class B limits (10 dB stricter) apply to residential use. Harmonized in the EU as EN 55011; the US counterpart is FCC Part 18.

Category: EMC Standards

Frequency: 150 kHz to 18 GHz

EU: EN 55011

Understanding CISPR 11

The International Special Committee on Radio Interference (CISPR) develops emission and immunity standards to protect radio services from interference generated by non-communication electrical equipment. CISPR 11 specifically addresses ISM equipment, a broad category spanning everything from laboratory power supplies to industrial RF welders and medical imaging systems. The standard establishes two key classification axes: Group (based on whether RF energy is intentionally generated) and Class (based on the intended operating environment).

Conducted emission limits cover the frequency range from 150 kHz to 30 MHz, measured at the AC mains port using a line impedance stabilization network (LISN) providing a defined 50 Ω impedance. Both quasi-peak (QP) and average (AV) detector readings must comply. Radiated emission limits cover 30 MHz to 1 GHz (measured at 10 m or 30 m distance depending on Class) and 1 to 18 GHz (measured at 3 m). Group 2 equipment operating in designated ISM bands (13.56 MHz, 27.12 MHz, 40.68 MHz, 915 MHz, 2.45 GHz, 5.8 GHz, 24.125 GHz) receives relaxed limits at those specific frequencies, acknowledging that some RF leakage is inherent to their function. Outside the ISM bands, Group 2 equipment must meet the same limits as Group 1. For the RF engineer, understanding these boundaries is critical when designing equipment that uses microwave energy for processing (plasma etching, RF drying, induction heating) since the emission profile must be managed through shielding, filtering, and careful PCB layout.

Key CISPR 11 Emission Limits

Conducted Emissions (150 kHz to 30 MHz):
Class A QP: 79 dBμV (0.15 to 0.5 MHz), 73 dBμV (0.5 to 30 MHz)
Class B QP: 66 dBμV (0.15 to 0.5 MHz), 60 dBμV (0.5 to 5 MHz)

Radiated Emissions (30 to 230 MHz):
Class A: 30 dBμV/m at 30 m ; Class B: 30 dBμV/m at 10 m

Distance Correction (free-space):
E_d2 = E_d1 + 20·log₁₀(d₁/d₂) [dBμV/m]

QP = quasi-peak detector, AV = average detector (typically 10 to 13 dB below QP for broadband sources). Class B at 10 m ≈ Class A at 30 m minus ~10 dB effective margin. LISN impedance: 50 Ω || 50 μH per MIL-STD-461/CISPR 16.

CISPR 11 Classification Summary

Classification	Equipment	Conducted Limit	Radiated Limit	ISM Relaxation
Group 1, Class A	Industrial (incidental RF)	79/73 dBμV QP	30 dBμV/m at 30 m	No
Group 1, Class B	Residential (incidental RF)	66/60 dBμV QP	30 dBμV/m at 10 m	No
Group 2, Class A	Industrial (intentional RF)	79/73 dBμV QP	30 dBμV/m at 30 m	Yes (at ISM freqs)
Group 2, Class B	Residential (intentional RF)	66/60 dBμV QP	30 dBμV/m at 10 m	Yes (at ISM freqs)

Common Questions

Frequently Asked Questions

What is the difference between Group 1 and Group 2?

Group 1 covers equipment with incidental RF generation (power supplies, motor drives, LED lighting). Group 2 covers intentional RF use for material processing (RF heaters, plasma systems, microwave ovens, electrosurgical units). Group 2 gets relaxed limits at ISM frequencies because some RF leakage is inherent to operation.

How do Class A and Class B limits differ?

Class A (industrial) limits are approximately 10 dB less restrictive than Class B (residential). Conducted: Class A = 79 dBμV QP at 0.15 to 0.5 MHz vs Class B = 66 dBμV. Radiated: Class A measured at 30 m, Class B at 10 m. EU consumer market requires Class B compliance.

How does CISPR 11 relate to FCC Part 18?

CISPR 11 is international; EN 55011 is the EU harmonized version (identical limits + CE marking). FCC Part 18 is the US counterpart with similar but not identical limits, different measurement distances, and different detector types in some bands. Global products typically test to both standards since CISPR 11 compliance doesn't automatically satisfy FCC.

Related Terms

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