Varistor selection for 230 V mains starts with a continuous AC rating above your highest supply voltage, then a disc size for the surge current: usually 275 Vac, a 430 V varistor voltage, in the UK. Of Walsin Technology (Walsin)’s 51 MOVs at 250, 275 and 300 Vac, 11 at 275 Vac exceed 4,000 A, from Venatech, the authorised Walsin distributor in Hong Kong.
Venatech Limited, an authorised Walsin distributor in Hong Kong, wrote this for a power electronics or controls engineer in the UK protecting a 230 V input on a charger, drive, appliance or industrial controller. We parsed Walsin’s metal oxide varistor export, Walsin_MOV_ALL.xlsx (379 distinct part numbers in 4 series), and checked our stock list as at 23 September 2026. The market figures name their source and the day we fetched them, 11 November 2026. This is engineering guidance, not compliance advice; confirm the surge and safety standards your product must meet with your compliance team.
Why is varistor selection for 230 V mains a live question in the UK now?
Because UK electrified manufacturing is growing. According to Tyrepress on 30 October 2026, reporting SMMT figures, UK vehicle production rose 36.3% in September 2026 to 74,031 units, car output rose 38.6% to 70,831, and electrified cars made up 42.3% of car output.
Those are the SMMT’s figures, not ours, and the SMMT itself notes the comparison is flattered by last year’s disruption. The engineering point we draw is ours: every electrified car needs charging, and every wall box, on-board charger, factory drive and test rig with a 230 V input needs a varistor across the line that survives the surges of a real grid for years. We say nothing about any company’s products.
How do you choose the AC voltage rating of a varistor for 230 V mains?
Above the highest voltage the product must run at continuously. Walsin’s export lists each MOV’s maximum working voltage in Vac beside its varistor voltage; at 230 V nominal, a design that must run at 230 V plus 10%, 253 V, needs a rating above 253 Vac, and the next step in Walsin’s ladder is 275 Vac with a 430 V varistor voltage.
The rule is simple: the continuous rating must exceed the highest sustained supply voltage, including the tolerance your product specification states, because a varistor running above its rating conducts continuously and overheats. Going too high costs you protection: a higher rating means a higher clamping voltage, which the protected circuit must withstand. Walsin’s 230 V-region steps are 250 Vac (390 V varistor voltage), 275 Vac (430 V) and 300 Vac (470 V), each with ±10% varistor voltage tolerance. Choose 300 Vac only where the supply is known to sit high or temporary overvoltages are long; otherwise 275 Vac is the usual balance for 230 V lines.
How do you choose the varistor disc size?
By the surge current you must survive, with margin for repeats. In Walsin’s export, the 275 Vac standard D series runs from 400 A peak at 5 mm through 1,200 A at 7 mm, 2,500 A at 10 mm, 4,500 A at 14 mm and 6,500 A at 20 mm to 18,000 A at 25 mm.
- Take the surge test your product standard specifies, its waveform and the source impedance, and estimate the peak current through the varistor.
- Pick a disc whose peak current rating exceeds it with margin; repeated surges lower the current a varistor can take each time, so a part rated far above the single-shot figure lasts longer.
- Check energy as well as current for long-duration surges; the high-energy series exist for that.
- Check the clamping voltage at your surge current against what the downstream circuit can tolerate.
- Confirm all of it against the maker’s datasheet curves, Walsin’s datasheet for a Walsin part, and a surge test on your own hardware.
Which Walsin 275 Vac varistors cover 230 V mains?
Seventeen, across four series. We counted 17 Walsin MOV part numbers rated 275 Vac with a 430 V varistor voltage: 6 standard D series from 5 to 25 mm, 3 high energy E series, 3 super high energy V series and 5 industrial parts up to 80,000 A; the export lists the same 17-part spread at each of 13 voltage steps from 130 to 420 Vac.
| Walsin part | Series | Disc | Max working voltage | Varistor voltage | Peak current | Match / mismatch for a 230 V, 4,000 A brief |
|---|---|---|---|---|---|---|
SR431K10D |
Standard (D) | 10 mm | 275 Vac | 430 V ±10% | 2,500 A | Mismatch: peak current below the brief |
SR431K14D |
Standard (D) | 14 mm | 275 Vac | 430 V ±10% | 4,500 A | Match, little repeat margin |
SR431K20D |
Standard (D) | 20 mm | 275 Vac | 430 V ±10% | 6,500 A | Match, more margin |
SR431K14E |
Super high energy (V) | 14 mm | 275 Vac | 430 V ±10% | 8,000 A | Match, twice the brief in 14 mm |
SR431K18E |
High energy (E) | 18 mm | 275 Vac | 430 V ±10% | 9,000 A | Match |
SR431K32D |
Industrial | 32 mm | 275 Vac | 430 V ±10% | 30,000 A | Match, panel-level protection |
SR391K14D |
Standard (D) | 14 mm | 250 Vac | 390 V ±10% | 4,500 A | Mismatch: 250 Vac is below 253 V |
SR471K14D |
Standard (D) | 14 mm | 300 Vac | 470 V ±10% | 4,500 A | Match, higher clamp voltage |
The 4,000 A brief is our example, not a standard’s figure: we checked all 17 275 Vac rows, and 11 are rated above 4,000 A, from the 14 mm standard part up to the 34 mm square industrial part at 80,000 A. For a 14 mm footprint, the super high energy SR431K14E doubles the peak current of the standard SR431K14D. For these lines, request a quote and we source them through our authorised Walsin channel; ask us for the Walsin datasheet before you commit. Our how to choose an MOV varistor and MOV series selection: D, E, V and industrial guides go further.
What else must sit around the varistor on a mains input?
A fuse, often a thermal disconnect, and the right capacitor class. We checked our own input-stage checklist against the 17-part range; it has 4 parts: a fuse or thermal protection ahead of the varistor, the varistor across the line, safety-rated X and Y capacitors for EMI, and creepage and clearance that suit the mains category.
- A varistor fails short when overstressed, so put a fuse upstream and consider a thermally protected arrangement where a sustained overvoltage is possible.
- Line-to-line and line-to-earth varistors may both be needed; the second faces the higher stress in some surge tests.
- EMI filtering after the varistor uses safety-certified X and Y capacitors; Walsin’s S2 and S3 MLCC series carry named third-party certificates, including UL file E182369.
- Placement: keep the varistor at the input, with short, wide traces, before any filter stage.
How can Venatech help a UK team pick the Walsin MOV?
How Venatech helps: send the mains voltage, the surge test and your current varistor, and we return the Walsin options by rating and disc. Venatech Limited is Walsin’s authorised distributor in Hong Kong; upload the whole BOM and our free VenaMatch tool, which decodes 18 manufacturers’ part numbers and crosses 800,000+ parts, handles the capacitor and resistor lines on the same input stage.
Upload a BOM to request a quote on the varistor lines, and paste the MLCC and resistor lines into the cross-reference tool. The ready-stock list is a Hong Kong snapshot dated 23 September 2026. Small lots from Hong Kong, no lead-time or stock promise. The MOV range lists the series.
The short version
For 230 V mains, choose a continuous AC rating above your highest supply voltage, usually 275 Vac with a 430 V varistor voltage, then a disc for the surge current with margin for repeats. Walsin lists 17 MOVs at 275 Vac from 400 A to 80,000 A, and in a 14 mm footprint the super high energy SR431K14E carries 8,000 A.
Send us your surge test level and the varistor you use now, and we will return Walsin options with disc size and peak current side by side. How many surges does your input see in its life?
Related reading
- How to choose an MOV varistor
- MOV varistor series selection: D, E, V and industrial
- MOV energy ratings: 40,000 A vs 80,000 A
- Free cross-reference tool and ready-stock snapshot
Last reviewed 11 Nov 2026.
Sources
Fetched 11 November 2026 unless stated.
- Tyrepress, “UK vehicle production rebounds 36% in September”, 30 October 2026: https://www.tyrepress.com/2026/10/uk-vehicle-production-rebounds-36-in-september/
- Walsin MOV export Walsin_MOV_ALL.xlsx and the Venatech stock list as at 23 September 2026, counted by us.
- Walsin MOV product search: https://www.passivecomponent.com/product-search/MOV
Frequently asked questions
What varistor rating should a UK product use on 230 V mains?
A maximum continuous AC rating above the highest supply voltage your product must run at, including its stated tolerance. For 230 V plus 10%, 253 V, the usual choice is 275 Vac with a 430 V varistor voltage.
Why not use a 250 Vac varistor on 230 V mains?
Because 250 Vac sits below 253 V, the upper end of a plus 10% band, so the varistor could conduct continuously at high line and overheat.
How many Walsin 275 Vac varistors are there?
We counted 17 part numbers rated 275 Vac with a 430 V varistor voltage, across the standard D, high energy E, super high energy V and industrial series, rated from 400 A to 80,000 A peak.
How do I choose the varistor disc size?
By the peak surge current your product standard implies, with margin for repeated surges, and by energy for long surges. In Walsin’s standard D series at 275 Vac, a 14 mm disc is rated 4,500 A and a 20 mm disc 6,500 A.
Does a varistor need a fuse?
Yes. A varistor fails short when overstressed, so place a fuse or thermal protection upstream. Confirm the arrangement against your product’s safety standard with your compliance team.
Can Venatech supply Walsin varistors in the UK?
Venatech is the authorised Walsin distributor in Hong Kong and serves small lots; upload a BOM to request a quote. We give no lead-time or stock promise and no compliance advice.