UL Standards #20 and #498

I’m looking for a copy of these standards.

Any help is greatly appreciated!


Does this work for you ?



I just want these 2 standards not $600 worth of all of them.

I’m looking for the actual statement in writing that the UL indicates as a temperature threshold for problematic electrical components such as switches, receptacles, breakers, etc.

I have learned that it’s reported to be 30°C (54°F) temperature difference between a component and ambient temperature. This threshold is supposed to be the defining indicator (from UL) of whether an electrical component is problematic or not.

I would just like to have this in writing rather than stating that I learned it in a class.

30c is 86f
Different equipment will have different thresholds. Breakers usually have 40c 104f molded in them but I couldn’t get NFPA interested in that when I asked about a panel full of AFCIs in a comment for the 2008 ROC.

U/L is a standards organization. They make money selling standards, not giving them away. I agree with you, when this gets adopted as law they should lose that protection … but it isn’t true.

You’re right…I wrote it down wrong and didn’t do the math myself.:oops:

(why I want it in writing)


Is there a rule of thumb with existing documentaion to back it up in existence? Or should it be more based on mfg statements and recommendations?

lol…you trouble maker you…thehehehe…

Even if you find the exact text of those specific standards, it probably will be necessary to also understand the conditions under which UL sets those parameters. For example, I would almost bet that they are based on a device operating at rated load in a 40C ambient, as that is the baseline ambient for many electrical devices. Thus, the ‘rule-of-thumb’ mentioned may not accurately represent an acceptable temperature rise under real-world conditions.

I understand what you’re saying.

But a wall switch or receptacle in a typical house should not be typically exposed to a 40C (104F) ambient (surrounding) temp. The ambient temp should be more in the 20C to 25C range. The UL standard is supposed to say that a switch that is 30C above the surrounding wall temp has a problem. If it’s 28C above the surroundings, it’s probably ok :-k

I don’t know… I want to see the standard and read for myself what the intentions are.

The 40 deg. marking refers to the max. ambient the component is intended to operate at. Not the max. component temp.

If the mfg. wants a higher marking. his component has to be tested and pass at the higher ambient temp for the max rise of all parts contained therein.

Some libraries have some UL standards. They are often very expensive and UL 498 is very thick as it covers many types of components.

Thanks Michael

In the case of a breaker, all I have been told is, that is what temperature it was calibrated, not the maximum temperature it will operate.

Thanks Greg

OK here’s the deal…

My original statement is correct:

and here is why… (infrared guys pay attention!)

The UL states that A difference of 30°C between ambient temperature and the temperature of electrical component indicates a problematic component. Soooo… doing the math…

Let’s say the ambient temperature of the wall is a 0°C and the measured temperature of the light switch is 30°C. this is a difference of 30° which indicates a problem acording to UL.

Now using the Fahrenheit scale 0°C =32°F (the measured temperature of the wall) and 30°C =86°F (the measured temperature of the light switch) which is a difference of 54° on the Fahrenheit scale.

Pretty darn confusing if you do ask me, but doing research of other technical papers this is the same way they list temperature differences.

Makes sense now don’t it! :wink:

As to copyright law, it may be that once the standard is adopted as public law, the author or copyright owner may lose the rights to it.

I remember reading something on this a few weeks back. It also depends on how the standard was written, but there is more to the story than this.