Chip Resistor Working Voltage vs Rated Power: 9,756 of 33,192 Walsin WR and MR Rows Cannot Reach Their Own Rating

A chip resistor’s working voltage, not its wattage, limits 9,756 of 33,192 Walsin WR and MR rows we tested: 29.4 percent. Above a case-size resistance, the printed rated power can never be dissipated. At 0805, 888 of 2,904 higher-rated MR rows are worth exactly the same as the lower-rated WR rating.

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the chip resistor parametric exports published by Walsin Technology (Walsin) and the two chip resistor approval sheets that go with them. This post is written from the general purpose files: every WR and MR row at a case size where a sheet prints a maximum operating voltage, tested against that sheet’s own formula. Every part number below is real. Every count is of part numbers, not pieces.

How many Walsin WR and MR chip resistors cannot dissipate their own rated power?

9,756 of 33,192, which is 29.4 percent. We read Thick_Film_General_Purpose_1_1_4W.xlsx and the other general purpose export files in full, then tested every non-jumper WR row at 1206, 0805, 0603 and 0402 (19,640 rows) and every MR row at 1210, 1206, 0805, 0603 and 0402 (13,552 rows). The approval sheets define rated continuous working voltage as the lower of the square root of rated power times resistance, and a ceiling printed per case size. Where the ceiling is the lower number, the export’s rated power cannot be reached. WR has 5,680 such rows and MR has 4,076.

The split is the same at both tolerances. 8,062 of 27,396 one percent rows and 1,694 of 5,796 five percent rows are voltage-limited. We have not seen this counted anywhere: a full-population test of the printed rated power against the sheet’s voltage rule, across both resistor sheets we hold. Our earlier post on high voltage chip resistors and the limit nobody checks established the rule on a subset of WR parts. This one runs it on all 33,192.

At what resistance does the voltage ceiling take over at each case size?

At the ceiling squared divided by the rated power, and that number is low. A 0402 rated 1/16 W stops being power-limited at 40 kilohm. We worked the crossover for every size and rating pair in the export, and the 1 megohm end of the range is voltage-limited at every one of them. The formula is the sheets’ own: RCWV equals the lower of root of power times resistance, and the tabulated ceiling.

Every size in the export carries the same 799 distinct resistance values, from 1 ohm to 10 megohm. So a quarter of the grid or more sits above the crossover at every pair above. Ceilings and ratings are from page 3 of Walsin_WR_General_Purpose_Chip_Resistor.pdf (ASC_WR_V24, September 2016) and Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf (ASC_MR_V13, March 2024).

How much of the rating is left at 1 megohm?

Between 0.25 and 16 percent, depending on the size. The dissipation a part can actually reach is the ceiling squared divided by the resistance. We computed that for all 33,192 rows and compared it with the printed rating: 8,367 rows (25.2 percent) can reach less than half of it, 5,064 (15.3 percent) less than a tenth, and 811 (2.4 percent) less than one percent. The worst case is the MR 0402 rated 1/10 W at 10 megohm: 0.25 milliwatt of 100.

Read MR10X1004FTL against WR12X1004FTL. The MR 1210 is rated twice the WR 1206 and, at 1 megohm, both deliver 40 milliwatts. The extra rating is paid for in board area and returned as nothing.

Does a 1/4 W MR 0805 outperform a 1/8 W WR 0805?

Only below 180 kilohm, and not above it. The MR sheet rates its 0805 at 1/4 W and the WR sheet rates its 0805 at 1/8 W, and both print a 150 V ceiling. We counted the MR rows rated above the WR rating at the same size: 2,904 across 0402, 0603 and 0805. On 888 of them (30.6 percent) the voltage ceiling flattens the advantage to zero: the MR part and the WR part can dissipate exactly the same power at that resistance.

We have not seen this counted anywhere. At 100 kilohm, MR08X1003FTL reaches 225 milliwatts and WR08X1003FTL reaches 125 milliwatts, so the MR rating is still worth 1.8 times there. At 180 kilohm and above, MR08X1803FTL and WR08X1803FTL both reach 125 milliwatts. The 1/4 W figure sits in the same Rated Power column and filters the same way at every resistance. The dissipation does not.

The pairing is not clean either. The MR export also holds 0805 parts rated 1/8 W under the same series name: MR08X1003FTLV is one. That mismatch against the MR sheet’s 1/4 W is covered in the automotive MR, SR and AEC-Q200 split. Both ratings share one ceiling, so the voltage test applies to each.

Which rows have no voltage ceiling in any datasheet we hold?

42,362 of 75,554 non-jumper general purpose rows, or 56.1 percent. We matched every row in the general purpose files against the case sizes the two sheets tabulate. The WR sheet tabulates a ceiling at four sizes and the MR sheet at five. The rows outside them are 13,552 WR 0201, 754 WR 01005, 3,018 WR 1210, 1,936 WR 1218, 3,184 each of WR 2010 and 2512, 3,872 MR rows at 0201, 1218, 2010 and 2512, and all 12,862 SR rows.

We will not extend the 29.4 percent to those rows. The formula would apply, but the ceiling is a number Walsin prints and we will not guess it. For the SR prefix, 0201 and the large sizes, ask us for the sheet. We hold 28 Walsin datasheets, 451 pages, and two are chip resistor sheets.

What should a sourcing engineer check before accepting a higher-rated power?

Three things, in order, and none is a column in the export. We read the Rated Power column across all 75,628 general purpose rows and found it carries watts only: there is no working-voltage column, no overload column and no derating column.

1. Compute the crossover. Take the ceiling for the size, square it, divide by the rated power. If your resistance is above that number, you are buying the ceiling, not the wattage.
2. Compare dissipation at your resistance, not rating. For a pull-up, bleeder or divider leg in the 100 kilohm to 10 megohm range, a 0402 and a 0805 differ by far less than their ratings suggest.
3. Cross the whole list in one pass on the free cross-reference tool. Paste up to 500 part numbers or drop an Excel or CSV. It is matched against Walsin’s published catalogue and states every difference from your original. Then check ready stock, a dated snapshot of 1,125 part numbers as at 23 September 2026 and not a live feed.

For the case-size rating ladder behind these numbers see chip resistor power rating by case size. The range sits on the Walsin chip resistor page. Confirm every figure against both datasheets and qualify in your own circuit.

The short version

We tested 33,192 Walsin WR and MR rows against the sheets’ working-voltage rule. 9,756 (29.4 percent) are limited by the voltage ceiling, not the wattage: WR 5,680 of 19,640, MR 4,076 of 13,552. The crossover is 40 kilohm at 0402 rated 1/16 W and 180 kilohm at 0805 rated 1/8 W. At 1 megohm a 1/2 W MR 1210 and a 1/4 W WR 1206 both deliver 40 milliwatts. On 888 of 2,904 MR rows rated above their WR counterpart, the higher rating is worth nothing. 42,362 rows sit at sizes with no ceiling in any sheet we hold. We will not tell you a higher rating is better. We will show you the resistance where it stops mattering. Qualification stays with you.

Send us the resistor lines off your BOM with the resistance values, and we will mark each as power-limited or voltage-limited against the sheet we hold. And a question back: how many of the 1/4 W parts on your bill of materials sit above 90 kilohm?

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