Varistor Selection for Poland: Which Disc Sizes Give You a Second Energy Grade

For varistor selection in Poland the question that decides a high-volume board is not which part, but which footprint keeps a second option open. Six of the eleven disc footprints Walsin Technology (Walsin) publishes offer two peak-current grades at the same working voltage. Five offer exactly one. 279 of the 379 part numbers sit on a footprint with a second grade.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds Walsin’s varistor parametric export of 379 rows. This post is written from that file. Every part number below is real and every count is a count of part numbers, not pieces. The reader we have in mind is a Polish appliance or industrial electronics manufacturer building in volume, where a footprint change after tooling costs far more than the part does.

Does Venatech have a Polish entity or Polish stock?

No. The operating entities are Venatech Limited in Hong Kong, the Shenzhen trading entity, VENATECH PTE LTD in Singapore and the Jiangmen factory in Guangdong, with Chengdu in preparation. Hong Kong is the authorised Walsin distribution entity and the origin of any shipment to Poland. There is no Polish office, no Polish warehouse and no local stock.

So the useful question to bring us is not “what can you deliver to Wrocław tomorrow”. It is “which part numbers exist at the intersection I have designed myself into, and what does the manufacturer’s data not state about them”.

Which varistor footprints let you change energy grade without changing the board?

Six of eleven. At any fixed working voltage in the mains band, the 5 mm, 7 mm, 10 mm, 14 mm, 20 mm and 34 mm square footprints each publish two part numbers at two different peak currents. The 18 mm, 25 mm, 32 mm, 40 mm and 53 mm footprints publish exactly one part number each, at any voltage.

Footprint	Parts in export	Peak current grades at one voltage	Series involved	Match / mismatch vs a drop-in energy upgrade
5 mm	41	400 A and 800 A	Standard and High Energy	Match — two grades, same footprint
7 mm	41	1,200 A and 1,750 A	Standard and High Energy	Match — two grades, same footprint
10 mm	53	2,500 A and 4,000 A	Standard and Super High Energy	Match — two grades, same footprint
14 mm	53	4,500 A and 8,000 A	Standard and Super High Energy	Match — two grades, same footprint
20 mm	49	6,500 A and 13,000 A	Standard and Super High Energy	Match — two grades, same footprint
34 mm square	42	40,000 A and 80,000 A	Industrial only	Match — two grades, one series
18 mm	20	9,000 A only	High Energy only	Mismatch — no second grade exists
25 mm	21	18,000 A only	Standard only	Mismatch — no second grade exists
32 mm	19	30,000 A only	Industrial only	Mismatch — no second grade exists
40 mm	19	40,000 A only	Industrial only	Mismatch — no second grade exists
53 mm	21	70,000 A only	Industrial only	Mismatch — no second grade exists

Unique to Venatech’s data. Of the eleven disc footprints in Walsin’s 379-row varistor export, exactly six publish more than one peak-current grade at a fixed working voltage and five publish exactly one. 279 of the 379 part numbers sit on a footprint where the surge rating is a selectable variable; the other 100 sit on a footprint where it is fixed by the geometry. Nothing in the part number signals it — the distinction only appears when the size column is cross-tabulated against the peak current column at a held voltage. For a volume build it decides whether a surge problem found in qualification can be fixed on the BOM or only by changing the board.

The series decode behind those pairs is ours and already published, in MOV varistor series selection: D, E, V and Industrial.

How much does the second grade actually buy you?

Between 1.46 and 2 times the peak current, and nothing else changes. We took the 275 Vac group — a common selection for a 230 V nominal mains input, and a group whose membership we have already published — and measured each pair.

Standard part	Upgrade part	Footprint	Peak current step	Multiplier	Match / mismatch on everything else
SR431K05D	SR431K05E	5 mm	400 A to 800 A	2.00×	Match — same voltage, same tolerance, same size
SR431K07D	SR431K07E	7 mm	1,200 A to 1,750 A	1.46×	Match — same voltage, same tolerance, same size
SR431K10D	SR431K10E	10 mm	2,500 A to 4,000 A	1.60×	Match — same voltage, same tolerance, same size
SR431K14D	SR431K14E	14 mm	4,500 A to 8,000 A	1.78×	Match — same voltage, same tolerance, same size
SR431K20D	SR431K20E	20 mm	6,500 A to 13,000 A	2.00×	Match — same voltage, same tolerance, same size
SR431K34R	SR431K34RD	34 mm square	40,000 A to 80,000 A	2.00×	Match — same voltage, same tolerance, same size

The multiplier is not uniform, and the 7 mm pair is the weakest upgrade in the range at 1.46×. If a 7 mm design is 50 per cent short on surge capability, the second grade at 7 mm does not reach it and the next step is a 10 mm hole pattern. That is worth knowing before the tooling is cut rather than after.

Note also that the upgrade letter is not a reliable marker. The 5 mm and 7 mm upgrades are High Energy parts and the 10 mm, 14 mm and 20 mm upgrades are Super High Energy parts, and all five carry the same trailing E. The 34 mm square pair is distinguished only by a trailing D.

Which footprints give you no second option at all?

Five, holding 100 of the 379 part numbers: 18 mm at 9,000 A, 25 mm at 18,000 A, 32 mm at 30,000 A, 40 mm at 40,000 A and 53 mm at 70,000 A. Each of those footprints appears in exactly one series across the whole file, so there is nothing to upgrade to without moving the holes.

The 18 mm exists only as a High Energy part — there is no 18 mm Standard and no 18 mm Super High Energy varistor in the export at all. The 25 mm is the mirror image: Standard only.

Is the biggest disc always the highest surge rating?

No, and this is where the ladder stops behaving like a ladder. The 53 mm disc is the largest footprint in the range and it is rated 70,000 A. The 34 mm square is smaller and its upgrade grade is rated 80,000 A. The 40 mm round disc is rated 40,000 A — the same figure as the lower of the two 34 mm square grades.

Part number	Footprint	Peak current	Series	Match / mismatch vs picking the largest disc
SR431K32D	32 mm	30,000 A	Industrial	Mismatch — smaller than 34 mm square and lower rated
SR431K34R	34 mm square	40,000 A	Industrial	Match — equals the 40 mm rating on less area
SR431K40D	40 mm	40,000 A	Industrial	Mismatch — more area, no more peak current
SR431K34RD	34 mm square	80,000 A	Industrial	Match — the highest peak current in the whole export
SR431K53D	53 mm	70,000 A	Industrial	Mismatch — largest footprint, not the highest rating

For a Polish industrial build this inverts the usual instinct. If the requirement is the maximum surge capability Walsin publishes, the answer is a 34 mm square footprint and the 34RD suffix, not the 53 mm disc. The 53 mm disc earns its place on voltage instead: it is the only footprint that reaches 750 Vac.

Does a footprint’s peak current ever change on its own?

Yes, at the bottom of the voltage range, and the part number does not tell you. Within the Standard series the 5 mm disc is rated 100 A on the eight part numbers from 11 Vac to 40 Vac and 400 A on the nineteen part numbers from 50 Vac to 420 Vac. The 7 mm disc does the same thing: 250 A below 50 Vac and 1,200 A at and above it.

That is a 4.0× step on the 5 mm disc and a 4.8× step on the 7 mm disc, inside one series and one footprint, triggered only by the voltage band. A low-voltage protection circuit designed on the assumption that a 5 mm Standard disc is a 400 A part will be wrong by a factor of four.

Do you hold a Walsin varistor datasheet?

No. Venatech holds no Walsin MOV datasheet and no public datasheet URL for this line. Every figure above is read from the parametric export.

What does Venatech add for a Polish volume build?

Three things a selector cannot. First, the structural counts above: which footprints carry a second grade, how big the step is, and where the ladder inverts. Second, a plain statement of what is missing — on this line we hold no datasheet, so a joule rating from us would be a guess. Third, a dated snapshot of what is physically in Hong Kong.

We will not tell you a part is equivalent. We will show you where it differs, field by field, and the qualification decision stays with you. The varistor range is on the Walsin varistor range page, and the reservation process is described in How to check Walsin stock and reserve it.

The short version

Six of Walsin’s eleven varistor footprints publish two peak-current grades at the same working voltage and five publish one, which puts 279 of 379 part numbers on a footprint where surge capability can still be changed on the BOM. The step is 1.46× to 2.00×, weakest at 7 mm. The largest disc is not the highest rated: 34 mm square reaches 80,000 A and 53 mm stops at 70,000 A. And at the bottom of the range the 5 mm and 7 mm discs change peak current by four times with no marker in the part number.

Tell us the footprint you have already committed to and the surge figure you need, and we will tell you whether a second grade exists on that footprint or whether the board has to move. For a Polish ship-to, ask for the delivery term and the lead time in the same message — everything moves from Hong Kong.

Faster than an email. The cross-reference tool takes a pasted list or a spreadsheet and returns Walsin candidates field by field, differences included. Ready stock shows what is physically in Hong Kong as a dated snapshot, so you can see whether a line is a stock pull or a production slot. Qualification stays with you.

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Frequently asked questions

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Three ways to get this answered today

1. Cross a part, free. 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 and returns candidates field by field, with every difference from your original stated rather than hidden. Filter by commercial or automotive grade, or for soft termination, high temperature, safety certified, high Q / low ESR or low profile. There is no login and no charge.

2. Send the whole BOM. Upload a BOM and request a quote and we will come back line by line — including the lines we cannot help with, which is usually the more useful half of the answer.

3. Check the shelf before you commit. Ready stock shows what was physically in Hong Kong as at 23 September 2026. It is a dated snapshot, never a live feed, and quantities are never permanent.

Why take our word for any of this? Don’t — check it.

Venatech Limited (威納電子有限公司) is an authorised Walsin Technology distributor in Hong Kong. Confirm that with Walsin rather than with us. On the safety capacitor series we hold UL file E182369, which is searchable in UL’s own public database, together with TUV certificates R50381780 and R50195920 and CQC CQC20001280137 and CQC20001280136, against EN 60384-14:2023, IEC 60384-14:2023 and UL 60384-14. We hold 28 Walsin datasheets, 451 pages, and we will send the one covering your part number. Shipments arrive in original sealed Walsin packaging with lot and date-code traceability, and a certificate of conformity is available per shipment on request.

We will also tell you what we do not hold, which no competitor publishes. REACH, SVHC, conflict minerals, PFAS, China RoHS, ISO 9001, IATF 16949, PPAP, IMDS and a Declaration of Conformity appear nowhere in those 451 pages. You would rather hear that from us now than from your own supplier-approval team later. AEC-Q200 is compliant in Walsin’s own words and never certified, we hold no manufacturer’s end-of-life or allocation list for any brand, and qualification in your own circuit stays with you. We will not tell you a part is equivalent. We will show you where it differs.

Venatech Limited · Unit 207, 2/F, Sun Ling Plaza, 30 On Kui Street, Fanling, N.T., Hong Kong · (852) 2628 4777 · Hong Kong, Shenzhen, Singapore and Jiangmen, with Chengdu in preparation.