An “EMC Class A / Class B” line is useful only when it names the standard, the tested configuration and the result it describes. For equipment procurement, the practical question is not which class sounds better. It is whether a complete conducted-emission report supports the exact assembly and operating arrangement being purchased.
This guide uses the WEHO LRS-35-24 as a concrete, conditional 24 V auxiliary-supply example. Its verified source photograph and approved specification establish its identity and nominal output, but they do not supply a conducted-emission report. No Class A or Class B claim is made for this unit or either illustrated machine.
Start with the applicable standard, not the letter
The IEC description of CISPR 32:2015 identifies multimedia-equipment emission requirements and two equipment classes. That scope matters: do not assume a particular multimedia standard applies to every industrial machine simply because a purchased supply has an EMC entry. The responsible compliance specialist should identify the product-family requirements, destination market and relevant edition for the finished equipment.
Once that basis is agreed, request the actual limit class used in the report. “Class B” without a standard number, edition and port is not a complete acceptance criterion. Similarly, a CE mark on a housing is not the measurement plot, report identity or tested configuration you need to review. Avoid turning a component description into a declaration for the assembled machine.
Illustrative bag-sealer control compartment: a screw-fixed LRS-35-24 supplies a conditional 24 V auxiliary-electronics branch. The sealing mechanism is a separate load; the scene is not an EMC laboratory or proof of machine compliance.
Conducted emissions are not the output-ripple row
A ripple-and-noise figure concerns a specified output measurement. A conducted-emission result concerns the applicable port, measurement arrangement and limit comparison. One does not replace the other. Do not accept a low ripple number as proof that a mains-port conducted-emission requirement has been met.
Keep three documents distinct in the purchasing file: the exact-model electrical specification, the conducted-emission report and the finished-equipment compliance assessment. Each answers a different question. If the report is unavailable, record it as unavailable rather than reconstructing a “pass” from the unit’s housing, filter appearance or certification icons.
Read the configuration beside the result
Texas Instruments’ PMP15013 reference-design test report is a useful example of configuration-specific evidence. It identifies a particular DC/DC board, describes its supply and load, and presents separate conducted-emission scans with and without a common-mode filter. It reports CISPR 22 Class B results for that board and setup—not for a WEHO AC/DC supply. The lesson is documentary: the tested configuration belongs with the plotted result.
For a supplier submission, ask for the complete pages that identify the equipment under test, sample or revision, input supply, output load, operating mode, wiring, enclosure arrangement and any required external filtering. A cropped graph may omit the very condition on which the result depends. Record which configuration is proposed for production, rather than treating every configuration in the report as interchangeable.
If an external filter, specified cable arrangement or enclosure bond was part of testing, ask how that requirement is controlled in the bill of materials and assembly instructions. Do not add a filter at random or assume a different installation inherits the original result. The review should establish the relationship between the tested setup and the delivered design before procurement marks the evidence complete.
Use the LRS-35-24 only within the facts actually supplied
The authentic label identifies LRS-35-24, a nominal 24 V, 1.5 A output and nominal AC input marking of 100–240 VAC, 0.74 A, 50/60 Hz. The extended input range in the approved family sheet is a separate specification statement; it is not a new label or evidence of conducted-emission performance. The series name is not a substitute for the exact output row.
The mechanical drawing maps the enclosure to an 82 mm front-terminal width, 99 mm front-to-rear depth and 30 mm height. It documents bottom and side M3 fixing positions with their own penetration limits. This is a screw-mounted enclosed supply, not a DIN-rail unit. Check the current drawing, protective arrangement and service access in the equipment design rather than putting it on a rail for convenience.
A separate benchtop filling-controller service pod uses the same exact supply in a different protected, dry location. Only the auxiliary branch is represented; no wet-area rating, whole-machine load or emission result is implied.
For a real bag-sealer or filling controller, first confirm that the intended electronics accept a 24 V rail and that their documented load profile fits the selected supply under the relevant conditions. Heater, actuator and main-drive circuits are not automatically included. Their ratings and switching behavior belong in the equipment review, not in an invented load budget derived from an illustration.
Unchanged authentic source detail: original WEHO artwork, full model, label ratings, five guarded front clamps and adjustment control. Product identity is evidence; the photograph is not an EMC test result.
A procurement record that exposes gaps
| Record | What to request | What it does not prove |
|---|---|---|
| Requirement | Applicable standard, edition, port, limit class and equipment scope | That a class label alone applies to the complete machine |
| Tested configuration | Exact sample/revision, input, load, operating mode, cabling, enclosure and external filter | That a changed arrangement has the same result |
| Measured result | Complete report, measurement plots, stated result and test conditions | That a specification-table entry is the underlying test |
| Production relationship | Controlled BOM and installation requirements linked to the report | That all alternative supplies or revisions are covered |
Missing evidence is actionable. Ask for the missing report, clarify a mismatched revision or return a class entry for correction. Do not silently fill the gap with a neighboring model’s report. Where the equipment design has changed, the responsible engineer should decide what assessment or testing is required; procurement should preserve that decision and its basis.
Engineering evidence flow: requirement → tested configuration → measured report → production relationship. The diagram contains no fabricated emission curve, threshold or WEHO pass result.
Questions worth sending with the purchase inquiry
Which standard and edition support the EMC Class A / Class B wording? Which ports and operating configurations are covered? Does the report identify this full model and revision? Are external filters or installation conditions mandatory? Who is responsible for evaluating the finished assembly? These questions make an EMC claim reviewable without promising that the illustrative equipment is already compliant.
Use the WEHO LRS-35 product page to identify the family, then request the current exact-model specification and applicable evidence with the quotation. Preserve the report boundary all the way from supplier selection to the production file.
