# What is the meaning of "ΩK" on a wirewound resistor?

Generally I see the letter "K" as "kΩ" and it means 1000Ω on a resistor. On this resistor iswriten 10 ΩK. The image of resistor is this:

What is the meaning of 10ΩK?

I want to replace it with one of the 10ΩJ resistors I have. Can these resistors (10ΩJ), take the place of a 10ΩK resistor?

The wattage of the resistors I'm going to replace is a bit bigger, I think wattage won't be a problem, am I right?

• Besides the fact that unit prefixes (k, M, G,...) are always written before the unit symbol (that's why they are called prefixes) 10000 Ohms is probably implausible (dependin on where you got that resistor from) as for dissipating 20W you need almost 450V rms.
– Curd
Mar 2, 2020 at 10:31
• So, what does this resistor measure with an ohmmeter? Mar 4, 2020 at 13:30

The "K" at the end is the tolerance value. "K" is 10%. The one marked 10ohms J is a 5% tolerance part.

Your 10 ohm K can be anywhere from 9 to 11 ohms. The 10 ohm J part can be anywhere from 9.5 to 10.5 ohms.

You can find the tolerance codes in this wikipedia article on marking codes.

You are planning to replace a lower precision, lower wattage resistor with a higher precision higher wattage part. That's fine.

• awesome,Great, so JRE would have one last question, should I use the metal or the stone? are there any differences Mar 2, 2020 at 10:51
• @mehmet physical size for one... Mar 2, 2020 at 11:05
• Rather strangely, the 10 ohm K cannot be anywhere from 9 to 11 ohms, it can be anywhere in the range [9 to 9.5] or [10.5 to 11] ohms. Otherwise it would be 5% rated (or better), not 10% rated. This happens because they make the resistors first, then test the exact resistance, and finally print the tolerance. The 1% tolerance resistors aren't made on better machines, they're just lucky. The same is true of capacitors and so on. Mar 4, 2020 at 7:09
• @AdamChalcraft It's true that you might see a bimodal distribution for some products, but it's not the case that you never see a better tolerance part in a lower tolerance bin. For example if the company makes an excess of 'good' parts, but needs to satisfy demand for lower tolerance parts. Mar 4, 2020 at 11:42

Ceramic body resistors:

The ceramic body resistor ("stone") has the very great advantage that it is designed to be "air cooled". If the leads are soldered into a PCB or to a tag strip then the resistor can dissipate its rated power in still air.

It is better to not operate them at full power, and they will become very hot (maybe well over 100 °C) if operated at full power, BUT they are designed to operate in this manner.

eg the Stackpole CB and MCB ceramic body resistors can be used at rated power in up to 70 °C ambient air. The MC are then derated linearly up to 155 °C and the MCB to 275 °C ambient air temperature (!!!)

Metal body resistors:

If operated at full rated dissipation the metal versions MUST be attached to a heatsink sized so that it can dissipate the power involved at an acceptable temperature. Used by themselves without a heatsink they could be operated at a much lower wattage.

eg the Ohmite Arcol HS25 is rated at 9W max without a heasink.

The Tyco THS25 is rated at 25 Watts at 25C with a heatsink and at 12.5 Watts with no heatsink.

The metal one can be heat sinked - that is what the screw tabs are for. I prefer them to the ceramic ones (the ones that you refer to as stone). The metal ones are usually more precise in value. Dale is likely the largest producer of the metal ones.

Also I'd invest in an ohmmeter (generally purchased as a multimeter). That way you can quickly measure a resistor for value and know if it is good, and if it is the correct value.

• if that is your 'community wiki' answer: Your answer is good, but it is wroth noting the ability to operate the ceramic bodied resistor at full rated power, whereas a metal unit designed for mounting to a heatsink is usually limited to a lower wattage if used without a heatsink. It MAY be that the init shown is suitable for most of 25W dissipation, but this is not certain without reference to a spec sheet. Whereas the ceramic unit is notionally suitable for 25w in-air use. I'd always derate such components substantially in practice. Mar 2, 2020 at 11:36
• @LaurinCavender: Are you intentionally making your answers "community wiki?" That's the second one from you I've seen today. It's unusual to make community wiki answers that often.
– JRE
Mar 2, 2020 at 12:05