4.4.5: Electro-magnetic Regulatory Compliance

Electromagnetic compatibility

Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage to operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment.[1]

Electromagnetic compatibility covers the following three classes of issues:[1]

1. Emission is the generation of electromagnetic energy, whether deliberate or accidental, by some source and its release into the environment. EMC studies the unwanted emissions and the countermeasures which may be taken in order to reduce unwanted emissions.
2. The second class, susceptibility, is the tendency of electrical equipment, referred to as the victim, to malfunction or break down in the presence of unwanted emissions, which are known as radio-frequency interference (RFI). Immunity is the opposite of susceptibility, being the ability of equipment to function correctly in the presence of RFI.
3. A third class studied is coupling, which is the mechanism by which emitted interference reaches the victim.

Interference mitigation and hence electromagnetic compatibility may be achieved by addressing any or all of these issues, i.e., quieting the sources of interference, inhibiting coupling paths and/or hardening the potential victims. In practice, many of the engineering techniques used, such as grounding and shielding, apply to all three issues.

EMC ensures the correct operation, in the same electromagnetic environment, of different equipment items which use or respond to electromagnetic phenomena, and the avoidance of any interference. Another way of saying this is that EMC is the control of EMI so that unwanted effects are prevented.

Besides understanding these phenomena, EMC also addresses the countermeasures, such as control regimes, design and measurement, which should be taken by the hardware systems design team in order to prevent emissions from causing any adverse effect.

Coupling

When a source emits interference, it follows a route to the victim known as the coupling path.

There are four basic coupling mechanisms:

1. conductive,
2. capacitive,
3. magnetic or inductive, and
4. radiative.

Any coupling path can be broken down into one or more of these coupling mechanisms working together.

• Conductive coupling occurs when the coupling path between the source and victim is formed by direct electrical contact with a conducting body.
• Capacitive coupling occurs when a varying electrical field exists between two adjacent conductors, inducing a change in voltage on the receiving conductor.
• Inductive coupling or magnetic coupling occurs when a varying magnetic field exists between two parallel conductors, inducing a change in voltage along the receiving conductor.
• Radiative coupling or electromagnetic coupling occurs when source and victim are separated by a large distance. Source and victim act as radio antennas: the source emits or radiates an electromagnetic wave which propagates across the space in between and is picked up or received by the victim.

Controlling EMI

The control of electromagnetic interference (EMI) and assurance of EMC comprises a series of related disciplines:

• Characterizing the threat.
• Setting standards for emission and susceptibility levels.
• Design for standards compliance.
• Testing for standards compliance.

Grounding and shielding aim to reduce emissions or divert EMI away from the victim by providing an alternative, low-impedance path. Techniques include:

• Grounding or earthing schemes such as ground planes for RF. The scheme must also satisfy safety regulations.
• Shielded cables, where the signal wires are surrounded by an outer conductive layer that is grounded at one or both ends.
• Shielded housings. A conductive metal housing will act as an interference shield. In order to access the interior, such a housing is typically made in sections (such as a box and lid); an RF gasket may be used at the joints to reduce the amount of interference that leaks through. RF gaskets come in various types. A plain metal gasket may be either braided wire or a flat strip slotted to create many springy "fingers". Where a waterproof seal is required, a flexible elastomeric base may be impregnated with chopped metal fibers dispersed into the interior or long metal fibers covering the surface or both.

EMC Testing

Testing is required to confirm that a particular device meets the required standards. It is divided broadly into:

• emissions testing and
• susceptibility testing.

Open-area test sites, or OATS, are the reference sites in most standards. They are especially useful for emissions testing of large equipment systems.

However, RF testing of a physical prototype (such as our network switch) is most often carried out indoors, in a specialized EMC test chamber. Types of test chambers include:

• anechoic,
• reverberation, and
• gigahertz transverse electromagnetic (GTEM) cell

It is important that the test equipment, including the test chamber or site and any software used, be properly calibrated and maintained. Typically, a given run of tests for a particular piece of equipment will require an EMC test plan and a follow-up test report. The full test program may require the production of several such documents.

Emissions are typically measured for radiated field strength and, where appropriate, for conducted emissions along cables and wiring.

Inductive (magnetic) and capacitive (electric) field strengths are near-field effects and are only important if the device under test (DUT) is designed for a location close to other electrical equipment.

For conducted emissions, typical transducers include the LISN (line impedance stabilization network) or AMN (artificial mains network) and the RF current clamp.

For radiated emission measurement, antennas are used as transducers. Typical antennas specified include dipole, biconical, log-periodic, double ridged guide and conical log-spiral designs. Radiated emissions must be measured in all directions around the DUT. Specialized EMI test receivers or EMI analyzers are used for EMC compliance testing. These incorporate bandwidths and detectors as specified by international EMC standards. An EMI receiver may be based on a spectrum analyzer to measure the emission levels of the DUT across a wide band of frequencies (frequency domain), or on a tunable narrower-band device which is swept through the desired frequency range. EMI receivers along with specified transducers can often be used for both conducted and radiated emissions. Pre-selector filters may also be used to reduce the effect of strong out-of-band signals on the front-end of the receiver. Some pulse emissions are more usefully characterized using an oscilloscope to capture the pulse waveform in the time domain.

Radiated field susceptibility testing typically involves a high-powered source of RF or EM energy and a radiating antenna to direct the energy at the potential victim or device under test (DUT). Conducted voltage and current susceptibility testing typically involves a high-powered signal generator, and a current clamp or other type of transformer to inject the test signal. Transient or EMP signals are used to test the immunity of the DUT against powerline disturbances including surges, lightning strikes and switching noise. The transient pulse may be generated digitally and passed through a broadband pulse amplifier, or applied directly to the transducer from a specialized pulse generator. Electrostatic discharge testing is typically performed with a piezo spark generator.

EMC test standards

EMC testing standards attempt to standardize product EMC performance, with respect to conducted or radiated radio interference from electrical or electronic equipment, imposition of other types of disturbance on the mains supply by such equipment, and the sensitivity of such equipment to received interference.[2]

For the United States, this includes:

• FCC Part 15 regulates unlicensed radio-frequency transmissions, both intentional and unintentional.
  • FCC Part 15 Subpart A contains a general provision that "devices may not cause interference and must accept interference from other sources."
  • FCC Part 15 Subpart B US limits and methods of measurement of radio disturbance, measuring radio waves accidentally emitted from devices not specifically designed to emit radio waves ("unintentional"), both directly ("radiated") and indirectly ("conducted")
  • The rest of FCC Part 15 (subparts C through H) deal with unlicensed devices specifically designed to emit radio waves ("intentional"), such as wireless LAN, cordless telephones, low-power broadcasting, walkie-talkies, etc.
  • Conducted emissions are regulated from 150 kHz to 30 MHz, and radiated emissions are regulated from 30 MHz and up.

The standards that likely will be referenced in network switch data sheets might include the following:

• Europe:
  • EN 55032:2015 +A11:2020, Class A
  • EN 55035:2017 +A11:2020 EN 61000‑3‑2:2014, Class A
  • EN 61000‑3‑3:2013

• U.S./Canada:
  • FCC CFR47 Part 15:2014, Class A (Code of Federal Regulations,Title 47). FCC Part 15 regulates unlicensed radio-frequency transmissions, both intentional and unintentional. FCC Part 15 Subpart A contains a general provision that "devices may not cause interference and must accept interference from other sources."[2]
  • ICES‑003 Class A

• Worldwide:
  • VCCI Class A
  • CISPR 32 Class A
  • CISPR 35:2016

NEBS

EMC Project Management Considerations

The project manager is responsible for determining how many prototype systems will be build at each prototype version or revision level and to whom they are allocated for what purposes. The initial prototypes are called "Proto 1" units.

When a "Proto 1" chassis with its system printed circuit board, power supplies, and fan trays is available as a complete system, one or more units usually are allocated to the EMC Compliance group. The EMC Compliance group conducts its testing as summarized earlier in this section, usually by running network traffic through the system. If the EMC Compliance group finds issues, they will work with the system design hardware team to find countermeasures that will be incorporated into the next revision (Proto 2 or Rev 2) of the chassis or PCB.

When the Proto 2 system units are available, the The EMC Compliance group conducts its testing again, and specifically checks that the countermeasures that were implemented are indeed effective.

When the EMC Compliance group believes that the system can pass the required testing standards, they can send systems to outside testing labs for testing and to receive the testing report that demonstrates compliance.

References

1. Electromagnetic compatibility - Wikipedia. Accessed February 17, 2026.
2. List of common EMC test standards - Wikipedia. Accessed February 17, 2026.
3. Voluntary Control Council for Interference by Information Technology Equipment - Wikipedia. Accessed February 17, 2026.
4. CES-003 — Information Technology Equipment (including Digital Apparatus). Accessed February 17, 2026.
5. Network Equipment-Building System - Wikipedia. Accessed February 19, 2026.
6. Figure \(\PageIndex{1}\): The four EMI Coupling modes. (By Steelpillow - Own work, CC BY-SA 3.0. Wikimedia - The four EMI Coupling modes.