Safety Capacitor Rated Voltage: 173 Rows Read 5,000 Vdc, None Is a Working Voltage

All 173 safety capacitor rows in Walsin’s MLCC export show a safety capacitor rated voltage of 5,000 or 6,000 Vdc. None of those is a working voltage. The approval sheet calls that field impulse voltage. The working rating is X1 310 Vac, Y2 250 Vac, 1,500 Vdc — and it appears in no export file.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 203 Walsin Technology (Walsin) parametric export files and 28 Walsin datasheets, 451 pages. This post is measured from 00_ALL_MLCC_parts_combined.xlsx, Walsin_DiscCap_ALL.xlsx and the approval sheet 16_Safety_X1Y2_General_S2.pdf. Every part number below is real. We established this defect on 6 October 2026 and published it then; what is new here is the scan we ran afterwards across every other series to see whether the same column lies anywhere else.

What does the Rated Voltage column actually say on Walsin’s S2 safety capacitors?

It states the peak impulse voltage, not the mains voltage the part sits across. We read all 173 rows of the Safety Certificated Caps X1/Y2 (S2 series) block in 00_ALL_MLCC_parts_combined.xlsx: 163 read 5000Vdc and 10 read 6000Vdc, and there is no third value. Page 2 of 16_Safety_X1Y2_General_S2.pdf names the field in the ordering key — the sixth position is headed “Impulse voltage”, with “502: 5000V Impulse Voltage” and “602: 6000V Impulse Voltage” spelled out underneath. Page 3 gives the figure a BOM tool never sees.

Field	What the export column says	What page 3 of the approval sheet says	Match / mismatch
Rated voltage, AC	no column exists	UL and TUV: X1 310 Vac and Y2 250 Vac	Mismatch — the governing rating is absent from the export
Rated voltage, DC	5000Vdc or 6000Vdc	All models 1,500 Vdc	Mismatch — the export figure is 3.3× to 4× the real DC rating
Peak impulse voltage	not labelled as impulse	5,000 V to 6,000 V	Match on the number, mismatch on the label
Termination finish	empty on 166 of 173 rows	Ni/Sn, lead-free	Mismatch — 7 rows carry +-10%, a tolerance, in the Termination column
Operating temperature	no column exists	−55 to +125 °C	Mismatch — not in any of the 203 export files

The part number carries the same trap. S242B471K502 ends in 502, and that 502 is 5,000 V impulse — not 50 V, not 500 V, and not a working rating. We have not seen this counted anywhere. A selector sorting by the Rated Voltage column puts all 173 of these parts at the top of the voltage list, four times above where they belong.

Is any other Walsin series’ Rated Voltage column mislabelled the same way?

No, and we checked all seventeen. We parsed every one of the 24,025 real rows in 00_ALL_MLCC_parts_combined.xlsx and took the maximum Rated Voltage in each series. Sixteen of the seventeen stop at or below 4,000 Vdc. The Middle to High Voltage series is named for its own span — 200V-4kV — and its measured ceiling is exactly 4,000 Vdc across 4,095 rows. Every single value above 4,000 Vdc anywhere in the export belongs to the 173 S2 rows. That is the cleanest form the answer could take: one series, one defect, no second instance.

Case size	Rows	Highest Rated Voltage excluding S2	Highest in S2	Plausible as a working voltage?
0402	3,991	250 Vdc	—	Yes
0603	4,730	250 Vdc	—	Yes
0805	4,912	1,000 Vdc	—	Yes
1206	3,520	2,500 Vdc	—	Yes
1210	1,370	2,000 Vdc	—	Yes
1808	419	4,000 Vdc	5,000 Vdc	No, on the 59 S2 rows only
1812	1,020	4,000 Vdc	5,000 Vdc	No, on the 34 S2 rows only
2211	57	no non-S2 row exists	6,000 Vdc	No — this case size is S2 only
2220	327	4,000 Vdc	5,000 Vdc	No, on the 23 S2 rows only

Two smaller findings came out of the same scan. 2211 is the only case size in the whole MLCC export with no non-safety row at all — all 57 of its parts are S2, so there is nothing at that footprint to sanity-check the voltage against. And the column has exactly one unit inconsistency in 24,025 rows: 1210N103J132 writes 1300V where every other row writes Vdc. That is a formatting defect, not a rating defect. A null result is still a measurement, and this one says the S2 block is a one-off rather than a pattern.

What happens when a BOM tool pushes 5,000 Vdc into a derating calculation?

It tells you the part is five times more capable than it is. Take a 470 pF Y-capacitor on a 230 Vac mains input. Derated at 50% of what the export states, S242B471K502 looks good for 2,500 Vdc of continuous stress. Derated at 50% of what page 3 of the approval sheet states, the same part is good for 750 Vdc and 155 Vac. That is not a rounding difference. It is a factor of 3.3, and it sits in the one place on the board where getting it wrong puts mains on the secondary side.

Part number	Line	Size or body	Capacitance	What the file states	Match / mismatch vs 470 pF X1/Y2 on 230 Vac mains
S242B471K502	S2 surface-mount X1/Y2	1808, 2.00 mm	470 pF ±10%	Export: 5000Vdc. Datasheet: X1 310 Vac, Y2 250 Vac, 1,500 Vdc	Match on class, capacitance and tolerance; mismatch — the export voltage is impulse, so read the datasheet
S252B471K502	S2 surface-mount X1/Y2	2211, 2.00 mm	470 pF ±10%	Export: 5000Vdc. Datasheet: same X1 310 Vac / Y2 250 Vac	Match on class and value; mismatch — larger footprint, identical electrical rating
YP0AC471K060	AC series leaded disc X1/Y2	leaded disc	470 pF ±10%	Export: X1-440Vac/Y2-250Vac	Match on class and value; mismatch — leaded, and the AC rating is stated in the clear
YP5AC471K060	AC series leaded disc X1/Y2	leaded disc	470 pF ±10%	Export: X1-500Vac/Y2-500Vac 1500Vdc	Mismatch — a different Y2 rating, 500 Vac, and the DC figure is published too
1808B471K402	Middle to High Voltage, 200V-4kV	1808, 2.00 mm	470 pF ±10%	Export: 4000Vdc, a genuine working rating	Mismatch — same size, same value, no safety approval, and a lower number than the S2 part

That last row is the one to sit with. Walsin’s dedicated high-voltage part at the same 1808 footprint, same X7R, same 470 pF, same ±10%, publishes 4,000 Vdc — a real continuous rating. The safety part beside it publishes 5,000 Vdc, a surge figure. Sorting by that column ranks the safety capacitor above the high-voltage capacitor, which is backwards. We will not tell you a part is equivalent. We will show you where it differs.

Why does the disc capacitor export get this right when the MLCC export does not?

Because the disc file uses a different column and a different convention. We read all 929 rows of Walsin_DiscCap_ALL.xlsx. Its voltage column is headed UR, and on all 367 safety rows it holds a string, not a number: eight distinct values, every one of them an AC working rating. X1-440Vac/Y2-250Vac on 57 rows. X1-400Vac/Y1-250Vac on 56. 126 of the 367 go further and append the DC figure too — X1-500Vac/Y2-500Vac 1500Vdc. Not one disc safety row states an impulse voltage.

So the same manufacturer, the same function and the same safety classes are published two ways in two files we hold. The leaded disc parts tell you the working voltage; the surface-mount S2 parts tell you a surge number and nothing else. A cross-reference tool reading both files cannot infer the convention from the data — it has to be told, line by line. We also hold no datasheet for any of the 929 disc rows, so there the UR string is all we have, and we say so rather than implying coverage.

Does the certificate you quote change the rated voltage?

Yes, and by 60 Vac. Page 3 of 16_Safety_X1Y2_General_S2.pdf gives two different rated-voltage lines for the same parts: “UL & TUV : X1 310Vac & Y2 250Vac & All model 1500Vdc”, and immediately beneath it “CQC : 250Vac”. So the X1 rating you may claim depends on which approval body your market cares about — 310 Vac under UL and TUV, 250 Vac under CQC — and neither figure is anywhere in the parametric data.

This is where a checkable credential beats an adjective. The S2 series carries UL file E182369, and a UL file number is searchable in UL’s own public database in about thirty seconds. Check us. The same sheet names TUV and CQC certificates against EN 60384-14 : 2023, IEC 60384-14 : 2023 and UL 60384-14 : 2025 (Ed 3.0) — Walsin lists those standards jointly, so do not map one standard to one certificate. Ask for the sheet covering your part number and it will be in your inbox rather than in a brochure.

Eighteen document types appear nowhere in our 451 pages, among them REACH, SVHC, PFAS, ISO 9001, IATF 16949, PPAP, IMDS and a Declaration of Conformity. We tell you what we do not hold.

What should a mains input designer in the Netherlands do before releasing the BOM?

Read the approval sheet for every Y-capacitor position, and never let a parametric field decide a safety rating. A Dutch power supply or industrial mains front end will have one or two Y-capacitor positions and a hundred decoupling positions, and the two Y positions are the ones where the export is wrong by a factor of 3.3. The trade press reported MLCC lead times of 26 to 32 weeks through 2026 as AI server and EV build-outs drew on the same capacity, which makes identifying a second source early worth more than it was two years ago.

1. Fix the class and the AC rating first, from the datasheet. X1 310 Vac and Y2 250 Vac on every S2 model, 1,500 Vdc on every S2 model. Those three numbers are the specification; 5000Vdc is a surge test result.
2. Cross the rest of the BOM in one pass. Paste up to 500 part numbers or drop an Excel or CSV file into the free cross-reference tool. It is matched against Walsin’s published catalogue, returns candidates field by field with every difference stated rather than hidden, and has a filter for safety certified parts specifically.
3. Check what is physically in Hong Kong on ready stock before you commit a build slot. That page is a dated snapshot as at 23 September 2026, not a live feed, and it held 3 safety capacitor codes and 864 MLCC codes on that date.

For the class distinction itself, see X1/Y1 vs X1/Y2 safety capacitors. For the rest of a Dutch mains front end, see mains input stage parts for the Netherlands. The surface-mount range is on the Walsin MLCC page.

The short version

Safety capacitor rated voltage is the one field in Walsin’s MLCC export you must not read. All 173 S2 rows show 5000Vdc or 6000Vdc; the approval sheet labels that field impulse voltage and gives the real rating as X1 310 Vac, Y2 250 Vac and 1,500 Vdc on every model, with CQC at 250 Vac. We scanned the other sixteen series and found no second instance — every value above 4,000 Vdc in 24,025 rows is an S2 row. The leaded disc file states AC working voltage in the clear on all 367 safety rows. Qualification stays with you.

Send us the Y-capacitor positions off your BOM and we will come back with the approval sheet, the AC and DC working ratings, and the Walsin candidates field by field — then tell you which of them was in Hong Kong on 23 September 2026. And if your selector has ever ranked a 5,000 V safety part above a 4,000 V high-voltage part, tell us: we would like to know how many tools do it.

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Frequently asked questions

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