Walsin Varistor Part Numbers: All 379 Have a One-Character Twin, and 42 Pairs Differ by 10x on the Same Footprint

Every Walsin varistor part number in the catalogue can be turned into a different real Walsin varistor part number by changing one character. We tested all 379 and found 887 such pairs. 42 of those pairs differ by at least ten times in varistor voltage and share an identical footprint, so the wrong part still fits the board.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the full metal oxide varistor parametric export published by Walsin Technology (Walsin) — Walsin_MOV_ALL.xlsx, 379 rows — and no varistor datasheet of any kind. None of the 28 Walsin datasheets we hold, 451 pages, covers this line. This post is written from that single export file, which is why every specification claim below is flagged and why we link only to Walsin’s own site for specifications. Every part number is real and checked against the export.

Does every Walsin varistor part number have a one-character twin?

Yes, all 379. We took the part number column out of Walsin_MOV_ALL.xlsx, substituted every character position with every other letter and digit in turn, and asked whether the result was also a part number in the same file. Every one of the 379 produced at least one hit. Across the whole file there are 887 distinct one-character-apart pairs. We have not seen this counted anywhere, and it is not a property any other Walsin line has to this degree, because a varistor code is only nine characters long and carries no redundancy at all.

Character position in SR680K05D	What it carries	Pairs in the file that differ only here	Varistor-voltage ratio across those pairs	Match / mismatch if you mistype it
1-2 (SR)	family prefix	0	—	Match — fixed on all 379 rows
3 (6)	first significant digit	185	1.15x to 6.83x	Mismatch on rating, match on footprint
4 (8)	second significant digit	315	1.04x to 1.80x	Mismatch on rating, match on footprint
5 (0)	decade multiplier	42	10.00x to 10.48x, every pair	Mismatch on rating, match on footprint
6 (K)	tolerance	0	—	Match — K on all 379 rows
7-8 (05)	disc diameter	257	1.00x, every pair	Match on rating, mismatch on footprint and surge
9 (D)	series letter	88	1.00x, every pair	Match on rating, mismatch on series and surge

Read that table as two halves. 542 of the 887 pairs change the electrical rating and keep the footprint. The remaining 345 keep the rating and change the footprint. There is no character in a Walsin varistor part number whose mistyping is harmless, and there is no character whose mistyping is obvious from the part arriving on the bench.

Which single character changes the rating by ten times?

The fifth. It is the decade multiplier in the three-digit varistor-voltage code, and all 42 pairs that differ only at position five differ by at least a factor of ten in varistor voltage — 10.00x at the low end and 10.48x at the high end. 84 of the 379 part numbers sit in such a pair. Nine two-significant-figure stems — 18, 22, 27, 33, 39, 47, 56, 68 and 82 — exist at two decades at once, and those stems account for 179 of the 379 rows.

Part number	Max Working Volt.	Varistor Voltage	Size	Peak Current	Match / mismatch against its one-character twin
SR180K05D	11 Vac	18 Vdc	5 mm	100 A	—
SR181K05D	120 Vac	180 Vdc	5 mm	400 A	Mismatch on voltage (10.0x) and surge (4.0x), match on 5 mm footprint
SR330K10D	20 Vac	33 Vdc	10 mm	500 A	—
SR331K10D	210 Vac	330 Vdc	10 mm	2,500 A	Mismatch on voltage (10.0x) and surge (5.0x), match on 10 mm footprint
SR470K10D	30 Vac	47 Vdc	10 mm	500 A	—
SR471K10D	300 Vac	470 Vdc	10 mm	2,500 A	Mismatch on voltage (10.0x) and surge (5.0x), match on 10 mm footprint
SR680K05D	40 Vac	68 Vdc	5 mm	100 A	—
SR681K05D	420 Vac	680 Vdc	5 mm	400 A	Mismatch on voltage (10.0x) and surge (4.0x), match on 5 mm footprint
SR820K10D	50 Vac	82 Vdc	10 mm	2,500 A	—
SR821K10D	510 Vac	820 Vdc	10 mm	2,500 A	Mismatch on voltage (10.0x), match on footprint and on peak current

The last pair is the one we would put in front of a reviewer. SR820K10D and SR821K10D share the disc diameter, the tolerance letter, the series and the same 2,500 A peak current, and are ten times apart on the only parameter that decides whether the part conducts on a normal mains cycle.

What do the two significant digits do if you get one of them wrong?

They move the rating without moving the board. 500 of the 887 pairs differ only at character three or character four, and the varistor-voltage ratio across those 500 runs from 1.04x to 6.83x — never wide enough to look obviously wrong, and never once changing the footprint. That is the dangerous band. A 10x error announces itself in a review; a 1.15x error does not. Position four alone carries 315 pairs, the busiest position in the file, and it is the second significant digit — the character a reader’s eye glides over fastest because everything around it still looks right.

Does a wrong footprint digit still give you a usable part?

It gives you a part with the identical electrical rating and up to 200 times the surge current. Characters seven and eight carry the disc diameter and characters nine the series letter; 345 of the 887 pairs differ only there, and in every single one of those 345 the Varistor Voltage column is identical. We checked all of them.

One voltage point shows what that means. 300 Vac / 470 Vdc is published on 17 part numbers in Walsin_MOV_ALL.xlsx, the most crowded electrical point in the file.

Part number	Series	Size	Peak Current	Match / mismatch against SR471K05D
SR471K05D	Standard (D Series)	5 mm	400 A	the reference
SR471K07D	Standard (D Series)	7 mm	1,200 A	Match on rating, mismatch on footprint and 3.0x surge
SR471K10E	Super High Energy (V Series)	10 mm	4,000 A	Match on rating, mismatch on footprint, series and 10x surge
SR471K18E	High Energy (E Series)	18 mm	9,000 A	Match on rating, mismatch on footprint, series and 22.5x surge
SR471K25D	Standard (D Series)	25 mm	18,000 A	Match on rating, mismatch on footprint and 45x surge
SR471K34RD	Industrial	34 mm Square	80,000 A	Match on rating, mismatch on footprint and 200x surge

Peak current at that one voltage point runs from 400 A to 80,000 A — a 200-fold spread — and the only thing separating the two extremes in the part number is the last three characters. A footprint typo on a mains input does not usually blow up on the bench. It fails the surge test eighteen months later, at the compliance lab, on a sample from a different reel.

Does the last letter of a Walsin varistor part number name its series?

No, and this is the trap we did not expect. 108 of the 379 part numbers end in the letter E. On 48 of them the Series column reads High Energy (E Series). On the other 60 it reads Super High Energy (V Series). The letter does not decide it. The two digits in front of it do: 05E, 07E and 18E are the E Series, while 10E, 14E and 20E are the V Series. We counted all 108 and we have not seen this counted anywhere.

Part-number tail	Series the export states	Part numbers	Match / mismatch against reading E as the E Series
05E, 07E	High Energy (E Series)	28	Match — the letter means what it looks like
18E	High Energy (E Series)	20	Match
10E, 14E, 20E	Super High Energy (V Series)	60	Mismatch — same trailing letter, different series
34R	Industrial	21	Mismatch — no D, no E, 40,000 A
34RD	Industrial	21	Mismatch — the only four-character tail in the file, 80,000 A

So a selector that routes on the trailing letter misfiles 60 of 108 parts into the wrong series, and a selector that routes on the final character alone cannot tell 34R from 34RD at all. Our own earlier count of that Industrial pair is in MOV energy ratings, 40,000 A against 80,000 A, and the four series are set out in MOV varistor series selection. The line itself sits on the Walsin MOV page.

What does this mean for a BOM line you inherited?

It means the part number on the line is not self-checking, and nothing in the export will catch a transcription error for you. Three of the nine characters carry the rating, three carry the footprint, and two are constant on all 379 rows — so only four characters of nine ever differ in a way a human notices. The tolerance letter is K on every row and the prefix is SR on every row; neither has ever told anyone anything.

We will not tell you a part is equivalent. We will show you where it differs — and on this line the first thing we check is whether the code you sent us has a twin, because on this line it always does.

1. Paste the surge-protection lines, not a filtered list. Up to 500 part numbers, or drop your Excel or CSV, into the free cross-reference tool. It matches against Walsin’s published catalogue and states every difference rather than hiding it.
2. Send the working voltage you need in Vac, not the varistor voltage. Max Working Volt. decides whether a part survives the mains; Varistor Voltage is the clamping reference. They sit next to each other and they are not the same question.
3. Check what is physically in Hong Kong on ready stock — 1,125 part numbers as at 23 September 2026, a dated snapshot and not a live feed.

Unit 207, 2/F, Sun Ling Plaza, 30 On Kui Street, Fanling, N.T., Hong Kong. (852) 2628 4777.

The short version

We substituted every character of every Walsin varistor part number and checked the result against the 379 rows of Walsin_MOV_ALL.xlsx. All 379 have at least one one-character twin; there are 887 pairs. 42 differ at the decade multiplier and every one is at least 10x apart in varistor voltage on an identical footprint. 500 more differ at a significant digit, between 1.04x and 6.83x apart, which is the band nobody catches. 345 keep the rating and change the footprint, where peak current at a single voltage point spans 400 A to 80,000 A. The trailing letter E names the E Series on 48 parts and the V Series on 60. We hold no varistor datasheet, so none of this can be checked against an approval sheet — which is exactly why we counted it.

Send us the surge-protection lines off your BOM and we will tell you, for each one, whether it has a one-character twin in Walsin’s catalogue and what that twin is rated at. And a question back: when a varistor part number on your BOM was last re-keyed from a PDF, who checked the fifth character?

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Frequently asked questions

<!– wp:rank-math/faq-block {"questions":[{"id":"faq-question-01","title":"How do I read a Walsin varistor part number?","content":"Nine characters on 358 of 379 rows, ten on 21. SR prefix, three digits of varistor voltage as two significant figures plus a decade multiplier, a tolerance letter, then two digits of disc diameter and a series letter. We decoded all 379 against Walsin_MOV_ALL.xlsx. The prefix and tolerance letter are constant on every row.”,”visible”:true},{“id”:”faq-question-02″,”title”:”Which character in a Walsin varistor part number is the most dangerous to mistype?”,”content”:”The fifth, the decade multiplier. We found 42 pairs in the file that differ only at that position and every one is at least ten times apart in varistor voltage while sharing an identical disc diameter. SR680K05D is 40 Vac and SR681K05D is 420 Vac. Both are 5 mm parts.”,”visible”:true},{“id”:”faq-question-03″,”title”:”Does Walsin publish a clamping voltage or an energy rating for its varistors?”,”content”:”Not in the parametric export. We read all ten column headers in Walsin_MOV_ALL.xlsx. There is no clamping voltage, no joules and no surge waveform, and three of the ten columns are empty on all 379 rows. We hold no varistor datasheet either, so for those figures go to Walsin’s own site.”,”visible”:true},{“id”:”faq-question-04″,”title”:”Does the letter at the end of a Walsin varistor part number tell me the series?”,”content”:”Not reliably. 108 part numbers end in E; 48 are High Energy (E Series) and 60 are Super High Energy (V Series). The two digits before the letter decide it. Industrial parts end 34R or 34RD instead, and those two tails differ by 40,000 A against 80,000 A of peak current.”,”visible”:true},{“id”:”faq-question-05″,”title”:”Can two Walsin varistors with the same voltage rating have different surge ratings?”,”content”:”Yes, by a very wide margin. 300 Vac and 470 Vdc is published on 17 part numbers, and their Peak Current column runs from 400 A on SR471K05D to 80,000 A on SR471K34RD. That is a 200-fold spread at one electrical point, decided entirely by the last three characters of the code.”,”visible”:true},{“id”:”faq-question-06″,”title”:”Do you hold a Walsin varistor datasheet?”,”content”:”No. Zero of our 28 Walsin datasheets, 451 pages, covers the varistor line, and we say so rather than imply otherwise. The 379 rows of the parametric export are everything we hold. Disc varistor approval sheets are on our request list; nothing has been sent to Walsin in writing yet.”,”visible”:true},{“id”:”faq-question-07″,”title”:”What should I send you to get a varistor crossed?”,”content”:”The incumbent part number and the maximum continuous working voltage in Vac. Paste up to 500 codes or drop an Excel or CSV into the free cross-reference tool. We will return Walsin candidates field by field with every difference stated, and we will tell you which published fields the varistor export simply does not carry.”,”visible”:true}],”listStyle”:””,”titleWrapper”:”h3″,”titleCssClasses”:””,”contentCssClasses”:””,”sizeSlug”:””} –>

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