EMC and LVD: managing two directives together for electronics

A power supply unit passes its electrical safety review with margin to spare. Two weeks before the first container is due to ship, the same unit fails radiated emissions on the final EMC run. An engineer adds filtering across the mains input, the emissions drop back inside the limit, and the schedule looks safe again. Then the safety reviewer asks the obvious question: what did those new components do to the touch current. This is the moment most electronics teams learn the real lesson of CE marking for electrical products. Electromagnetic compatibility and electrical safety are not two errands you run one after the other. They are two constraints on the same hardware, and a change made to satisfy one almost always moves the other.

Two directives, one piece of hardware

Most mains-powered electronics sold in the EU fall under two directives at once: the Electromagnetic Compatibility Directive (2014/30/EU) and the Low Voltage Directive (2014/35/EU). What each one covers in detail belongs on its own service page. What matters here is that both land on the same hardware at the same time, so neither can be settled in isolation.

These are not alternatives. A switching power supply, an LED driver, a household appliance or an industrial controller usually has to satisfy both directives at once, and then carry a single CE mark that stands for every directive that applies. Both are normally handled by self-declaration rather than through a Notified Body, which means the manufacturer, not an outside body, takes responsibility that both sets of essential requirements are met. That single signature is the reason the two belong in one project rather than two, and why a team that splits them across separate owners tends to pay for it later.

Where the two directives pull against each other

A combined approach matters because a fix in one domain routinely creates a problem in the other. None of these are edge cases. They are the daily texture of an electronics design review.

• Filtering versus leakage current. Y-capacitors placed between the live conductors and the chassis are a standard way to pull conducted emissions back inside the limit. Those same capacitors raise the touch current that the safety standard caps, so pushing hard on emissions can breach a safety requirement.
• Earthing and bonding. The protective earth is both a safety feature and the return path that EMC design relies on. A grounding scheme that reads cleanly on a schematic can still fail emissions, and an EMC-driven bonding change can weaken the protective earth the safety case depends on.
• Shielding and heat. Enclosures, shields and ferrites added to contain emissions change the way the product sheds heat. A thermal margin that satisfied the safety assessment can quietly vanish.
• Creepage, clearance and layout. Insulation distances fixed for safety constrain the board layout, and that layout is exactly what drives emission and immunity behaviour. You cannot freeze one side without moving the other.

Run electromagnetic compatibility and safety as separate workstreams and these collisions surface late, when the design is hardest and most expensive to change. Run them as one and the trade-offs get settled on the bench, early, by the same people who understand both sides.

A combined testing strategy, not two separate projects

Managing the two directives together is mostly a matter of sequence and discipline. A practical order looks like this.

Decide what actually applies first

Confirm the regulatory scope before any test is booked. If the product transmits radio on purpose, through Wi-Fi, Bluetooth or any radio module, it falls under the Radio Equipment Directive, 2014/53/EU, which takes in both the electromagnetic and the safety requirements, so EMC and the Low Voltage Directive do not apply alongside it. If there is no radio and the working voltage sits inside the low-voltage band, you are firmly in EMC plus Low Voltage Directive territory. The boundaries deserve attention: a 12 V device powered by an external mains adapter can sit outside the Low Voltage Directive while the adapter carries it, yet the complete assembly still has to meet the electromagnetic requirements. Electrical equipment built into machinery is another boundary, where safety is often addressed through the Machinery Directive instead.

Pick the standards for safety and EMC together

Choosing harmonised standards as a single set keeps the test plan coherent: a safety standard such as EN 62368-1, the EN 60335 series or EN 61010 depending on the product family, sitting alongside the EMC emission and immunity standards such as EN 55032, EN 55035 and the relevant parts of the EN 61000 series. Applying harmonised standards earns a presumption of conformity, which is the cleanest position to hold when you are declaring conformity yourself. Selecting them apart is how a safety choice ends up undermining an emission result that nobody re-checked.

Test early, then freeze the design once

Pre-compliance EMC scans during development catch emission problems while the board is still cheap to change. Pair them with a design review of insulation, creepage distances and protective earthing. Once both look sound, freeze the design and run the formal campaign on the same representative samples, in realistic operating modes. Here is the discipline that saves projects: any change made to pass electrical safety testing or to clear an emissions failure can invalidate the other result, so keep changes under tight control and re-test whatever the change touched.

Converging the paperwork: one technical file, one Declaration of Conformity

The administrative reward for handling the two together is concrete. The product needs one technical file, not two. The discipline that single file demands is coordination: a change logged for one directive has to be reconciled against the other before it lands, or the file can end up sound for one half and quietly broken for the other. From that single file you draw up one EU Declaration of Conformity that names every applicable directive together: EMC, the Low Voltage Directive, and in most cases RoHS, plus Ecodesign for energy-related products. There is still one CE mark, and it represents all of them. Treating the CE marking as the output of a single coordinated file, rather than a stack of separate certificates, is what keeps the claim defensible.

Because the standard route for both is self-declaration, no Notified Body signs the outcome. EMC offers an optional Notified Body assessment, generally used when harmonised standards are not applied in full, but in most cases the responsibility and the burden of proof rest entirely with the manufacturer. That is the strongest reason to base both the safety and the EMC claims on accredited testing, even when nobody outside the company is obliged to.

The mistakes that show up on the bench

• Two silos, two timelines. Safety sent to one lab and EMC to another, with no shared design authority, is how contradictory fixes get made in the first place.
• EMC left until last. Emissions failures found after the design is frozen are the most expensive kind, because the fix so often reopens the safety file.
• Assuming compliant parts make a compliant product. A CE-marked power module or sub-assembly does not guarantee that the finished system passes. EMC behaviour depends on the whole configuration, its cabling and its installation.
• Reading self-declaration as no testing. Declaring conformity yourself does not lower the bar. It raises your exposure if the file cannot show that the essential requirements are met.
• Letting the file drift. A later design revision that never reaches the technical file or the Declaration of Conformity quietly invalidates the CE marking it was supposed to support.

Plan them as one conformity project

Electromagnetic compatibility and electrical safety reward the teams that plan them together from the first design review: shared standards, early pre-compliance, one frozen design, one technical file and one declaration. If the product also leaves the EU, the same evidence can travel, since a CB test report can remove repeated safety testing across many national schemes. When you are ready to map the route for a specific product, the detail of what each assessment involves is set out on the dedicated service pages.