Conducted Emissions Testing

Conducted emissions testing measures the radio frequency noise a product pushes back onto its AC or DC power cable, and on some products its telecom and network cables, typically from 150 kHz to 30 MHz. Standards such as FCC Part 15B, ICES-003 and CISPR 32 set the limits, and most mains-powered electronic products sold in the US, Canada or Europe have to meet them.

The reason is simple. Noise that leaves on the wiring reaches every other device on the same circuit, and at higher frequencies the same cables start to radiate it, which is why the standards hand over to radiated emissions testing at 30 MHz.

Limits come in two classes. Class B covers products used in homes and is the tighter of the two. Class A covers equipment used in commercial and industrial settings, and the product standard, together with where the product will be sold and used, decides which one applies.

If it plugs into the mains, yes. Mains-powered products need AC conducted emissions testing as well as radiated emissions testing. Products that run only on internal batteries, with no way to operate while plugged in, do not need the AC mains measurement. If yours runs while charging, uses an AC adapter or takes power from another plugged-in device such as a computer’s USB port, it does.

Some standards also measure DC power ports and wired network ports such as Ethernet, so telecom, networking and industrial control products can carry more than one conducted test.

The market sets the standard: FCC rules in the US, ICES in Canada, the EN versions of the CISPR standards in Europe and the UK, and national editions of the same CISPR methods in Japan, Korea and Australia.

Most failures trace back to the power input. The usual causes we see:

• Switching power supplies. Fast switching edges produce noise at the switching frequency and its harmonics, often right where the limit is tightest.
• An undersized or missing input filter. A filter chosen from a datasheet may not suit the real load, the real layout or the real cable.
• Grounding and Y-capacitor placement. A good filter placed in the wrong spot, or returned to a poor ground, lets common-mode noise straight past it.
• An external adapter that passes alone. A supply that is compliant on its own bench can fail once it powers your product, because the load and the cabling have changed.

Finding this at the design stage costs far less. An EMC pre-scan shows where you stand before you commit to the accredited run.

The product sits on a non-conductive table above a reference ground plane, or on insulating supports on the floor if it is floor-standing equipment. Its power cable runs to a line impedance stabilization network (LISN), also called an artificial mains network. The LISN presents a defined impedance to the product, so results repeat from lab to lab, and passes the noise on each line to the receiver.

Cable length and routing follow the standard, because a loop of excess cable can change the result.

1. Scope the test. We confirm the standard, the class, the ports to be measured and the operating modes with you.
2. Set up and preview. The product runs on the LISN and we take a fast peak scan across the frequency range on each line.
3. Find the worst case. We compare operating modes and cable arrangements and keep the one that produces the highest emissions.
4. Measure against the limit. The highest peaks are measured with the quasi-peak and average detectors the standard calls for and compared with the limit line.
5. Report or diagnose. You receive an accredited test report with margins. If a frequency fails, we show you where and help find the source before a retest.

The core measurement is the voltage on each mains line, taken through the LISN, as FCC Part 15B, ICES-003, CISPR 32 and CISPR 11 require. Where the standard calls for it, wired network ports such as Ethernet are measured too, through an impedance stabilization network.

Automotive electronic modules are measured to CISPR 25 and EN 55025, alongside ISO 11452-2 and ISO 11452-4 immunity testing for the same component.

Industrial machines, lab instruments and medical devices are measured to CISPR 11 and EN 55011 on the LISN like any other mains product. For installed equipment that cannot come to the lab, CISPR 11 assesses radiated emissions on site; see radiated emissions testing.

We also support MIL-STD-461 conducted emissions, such as CE102, delivered through our in-house partner lab.

Some of the standards we test to include:

Our testing is ISO/IEC 17025 accredited by A2LA under certificate 5179.02; see our accreditations. Mains harmonics and flicker to IEC 61000-3-2 and IEC 61000-3-3 are covered on our harmonics and flicker testing page.

• Conducted emissions measured from 9 kHz to 30 MHz; the AC mains limits in FCC Part 15B, ICES-003 and CISPR 32 run from 150 kHz to 30 MHz
• Measured on a dedicated ground-plane test site with horizontal and vertical reference ground planes
• 16 A single-phase LISN calibrated to CISPR 16-1-2
• CISPR 16-1-1 compliant EMI receivers with peak, quasi-peak and average detectors
• Impedance stabilization networks for Ethernet and telecom ports
• Radiated emissions for the same product in our 10 m semi-anechoic chamber

Accredited and recognized. ISO/IEC 17025 accredited by A2LA (certificate 5179.02), FCC recognized, and ISED recognized under CAB CA0102.

One campaign for North America. FCC Part 15B and ICES-003 are measured in the same setup, and CISPR 32 for Europe can run in the same visit.

Installed equipment is covered too. For machines that cannot ship, CISPR 11 on-site testing is part of our accreditation, and our radiated emissions page explains how it works.

The whole compliance package in one lab. EMC, environmental and product safety testing all run at our lab in Aurora, Ontario, so a CE marking program stays with one supplier.

• Product type, a short description and photos
• Power: AC mains, DC or battery; voltage, phase and rated current
• Dimensions and weight, and whether it is table-top or floor-standing
• Operating modes, and which one you expect to be noisiest
• Target markets and the standard, if you know it, including Class A or Class B
• Cables and ports: power, DC, Ethernet and other wired connections, with lengths
• Samples available, and any support equipment the product needs to run
• Whether you want a pre-scan before the formal test

Send us the details and we will confirm the requirement and quote it.