What Actually Differs Between the KSW and KSY Versions?

The surge current and the energy rating - and nothing else. Same varistor voltage, same AC and DC working voltages, same clamping voltage, same disc dimensions.

Eight of those ten rows are identical, including the disc geometry. The doubling is not a bigger part. It is a different construction of the same 20 mm disc, and the two figures come from two separate documents.

Surge current, 8/20 µs waveform. Scaled to 13,000 A.

Energy, 10/1000 µs waveform. Scaled to 475 J. These are two different tests - do not read one as a conversion of the other.

Which Letter Carries the Surge Rating?

W does, and Y does not. In the manufacturer's own part-number decoder, W is defined as "high surge series, RoHS compliant". Y is defined as "RoHS Compliant" - an environmental suffix that applies across the whole TVR range, not a surge grade.

Here is the decoder table for the high-surge series, quoted from the datasheet:

And the decoder table for the standard series, in the same position:

So the two letters do not sit on the same axis. W raises the surge rating. Y declares RoHS. Comparing them as if they were two grades of the same thing is what produces the wrong answer.

Where the confusion comes from

The standard-series decoder lists Y in two different rows of the same table. It appears at position 10 as an appearance code - one of the kink-lead options - and again at position 11 as an optional suffix meaning RoHS compliant.

So the same one of eleven characters carries a mechanical meaning in one reading and an environmental one in the other. That is enough to make "KSW versus KSY" read like a like-for-like swap. It is not one.

Both parts share the same first ten characters - body size, voltage code, tolerance and lead form. Only the eleventh decides the surge rating.

Where the 6,500 A and 13,000 A Numbers Come From

Two different datasheets, and neither one contains the other's number. That is why the comparison is hard to make from a single document.

The standard TVR series datasheet, 2018 edition, lists TVR20561 at 6,500 A and 220 J. The TVR-D high-surge datasheet, 2025 edition, lists TVR20561-D / TVR20561KSW at 13,000 A and 475 J. Search either document for the other number and you find nothing.

The two series also cover different territory, which is worth knowing before you treat them as interchangeable:

The high-surge series does not go down to Φ5 mm and does not reach the top of the standard series' voltage range. If your design lives at either extreme, one of the two is simply not available to you.

The waveform condition matters here

The two headline figures are measured on different surges. 6,500 A and 13,000 A are 8/20 µs current ratings. 220 J and 475 J are 10/1000 µs energy ratings.

Both series quote both numbers, so the comparison is valid row by row - but do not convert one into the other. A part chosen on its 8/20 µs current rating may behave differently under a 10/1000 µs event, and the two columns are there because they answer different questions.

How to Read the Full Part Number

Eleven positions, and only the eleventh decides the surge class. Working through TVR20561KSW from the manufacturer's decoder:

Note position 9: K is the tolerance code, not a surge code. It appears in both part numbers and in the high-surge suffix table as well, which is another reason the string is easy to misread.

When to Choose Each

Choose the TVR20561KSW (high-surge) when:

• Your surge environment is severe - outdoor or utility-fed equipment where a 10/1000 µs event could deliver well over 220 J to the part.
• You are protecting against repeated or high-amplitude transients, and the standard part's 6,500 A margin is thin.
• You need the higher energy rating specifically. 475 J against 220 J is the bigger of the two jumps.

Choose the TVR20561KSY (standard) when:

• Your transient profile sits comfortably inside 6,500 A and 220 J. Doubling the surge rating buys nothing if the environment never approaches the first number.
• You are replacing a standard-series part and the surrounding circuitry was designed around its clamping behaviour.
• You need a Φ5 mm or a lower-voltage body - the high-surge series does not cover those.

Do not do this: treat KSW and KSY as interchangeable because the first ten characters match. They match because the difference lives entirely in the eleventh.

What About Pricing & Availability?

The high-surge series carries a construction premium, and the two ranges are not the same size: the standard series spans 11 to 1,000 V_ac across five body sizes (Φ5–Φ20 mm), while the high-surge series covers 115 to 680 V_ac across four (Φ7–Φ20 mm).

Rather than quote a figure that moves, we would rather check your quantity against the range you actually need.

Send us the surge waveform you are designing against, the energy per event, and the quantity, and we will confirm which of the two fits and quote it.

Frequently Asked Questions About TVR20561KSW vs TVR20561KSY

Q1: What is the difference between the TVR20561KSW and the TVR20561KSY?

A: The surge rating and the energy rating. The KSW is rated 13,000 A on an 8/20 µs surge and 475 J on 10/1000 µs. The KSY is rated 6,500 A and 220 J. Every other published parameter is identical, including the disc dimensions.

Q2: Does the W suffix mean a higher surge rating?

A: Yes. The manufacturer's decoder defines W as "high surge series, RoHS compliant". It is the marker that puts the part in the high-surge series.

Q3: Does the Y suffix mean a lower surge rating?

A: No. Y is defined as "RoHS Compliant" - an environmental declaration, not a surge grade. It is available across the standard series and says nothing about transient performance.

Q4: Then why do the two parts have different surge ratings at all?

A: Because they are in different series. The KSY is a standard TVR series part; the KSW is a TVR-D high-surge part. The surge rating comes from the series construction, and the eleventh character is how the series is declared.

Q5: Are the two parts the same physical size?

A: Yes. Both are listed at 4.4 / 6.3 / 3.2 mm on a Φ20 mm disc. The doubling in surge performance is not achieved by making the part bigger.

Q6: Can I swap a KSY for a KSW directly?

A: Mechanically yes, electrically with care. The footprint and the varistor voltage match, but the clamping behaviour of a high-surge disc under a fast transient is not identical, and the surrounding circuit may have been tuned to the standard part.

Q7: Is 13,000 A comparable to 475 J?

A: They are different tests. 13,000 A is the maximum surge current on an 8/20 µs waveform. 475 J is the maximum energy on a 10/1000 µs waveform. Both series publish both figures, so compare them row by row rather than converting.

Q8: Which body sizes are available in the high-surge series?

A: Φ7 mm to Φ20 mm, with AC working voltages from 115 to 680 V. The standard series covers Φ5 to Φ20 mm and 11 to 1,000 V_ac.

Q9: What does the K at position 9 mean?

A: The tolerance on the varistor voltage - K is ±10%. It is not a surge code, even though the standard and high-surge decoders both use K elsewhere in their suffix tables.