Square D Circuit Breaker. 40 deg.???

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frizbeedog

frizbeedog

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Square D, QO Breaker, 2 pole:

What does the 40 deg. marking mean that is stamped on it?

This is other than the temination ratings below, right, which you can't see too good here.

Sorry for the poor picture.

View attachment 1367
 
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That's the ambient temperature rating of the breaker used for calibration. It has nothing to do with the terminals or the conductor connected to it.
 
infinity said:
That's the ambient temperature rating of the breaker used for calibration. It has nothing to do with the terminals or the conductor connected to it.
Click to expand...

I never confused it for the termination rating but for years it has bugged me.

Thanks for that. :smile:

Does this marking serve any purpose for the end user?
 
frizbeedog said:
I never confused it for the termination rating but for years it has bugged me.

Thanks for that. :smile:

Does this marking serve any purpose for the end user?
Click to expand...


I didn't think that you did given the information in the OP. Figured I throw that is in case someone else was unsure.:rolleyes:
 
40degC is the ambient temperature that a breaker is calibrated for as part of the UL489.
When using a specified test procedure a UL489 listed breaker should carry its current rating continuously without tripping. If you look at the time/current curve it will be based upon 40deg.C.
Yes, breakers are available calibrated at special ambient temperature of which 50degC is the most common. However you will note that they will not be UL489 listed.
 
templdl said:
40degC is the ambient temperature that a breaker is calibrated for as part of the UL489.
When using a specified test procedure a UL489 listed breaker should carry its current rating continuously without tripping. If you look at the time/current curve it will be based upon 40deg.C.
Yes, breakers are available calibrated at special ambient temperature of which 50degC is the most common. However you will note that they will not be UL489 listed.
Click to expand...

When I read this my first thought was "how did he know that?"

Occupation:
Former Electrcial Distribution Protection and Controls Application Engineer
That explains it.:)
 
I had a problem once upon a time with branch breakers tripping in a subpanel in the boiler room of a small manufacturing plant. The problem was due to exceeding the 40deg C temp that the breakers are set up for. It was normally 120F in that boiler room. The problem was solved by adding a powered damper and a fan to the room to reject heat into the manufacturing floor.
 
Im glad Im not the only one that was bugged about that 40c stamp! I've also had situations when ambient temp was a factor. I never new you could get a breaker with a higher (50c) rating.
 
mdshunk said:
I had a problem once upon a time with branch breakers tripping in a subpanel in the boiler room of a small manufacturing plant. The problem was due to exceeding the 40deg C temp that the breakers are set up for. It was normally 120F in that boiler room. The problem was solved by adding a powered damper and a fan to the room to reject heat into the manufacturing floor.
Click to expand...

Bet those manufacturing floor folks were happy about any extra heat . . .

Best Wishes Everyone
 
Remember that 50deg.C breaker are not UL and can not be installed in a listed panel.
Remember the a 40degC calibrated breaker that is not carrying its rated current and trips on thermal because of a high ambient temperature is also protecting the conductor which is also being exposed to the same ambient temperature. The breaker is protecting the conductor as it should be and should never be considered as a nuisance trip.
If you were to install a 50deg.C breaker it would change the protection as everything had been based on a 40degC device.
The only place where I have provided 50degC calibrate breakers is to OEMs when they engineer control panels to use them.
They a special order breaker for the most part and require an extended lead time which a lot of time are not acceptable.
As such I as them to calculate their load and compare it to a 40degc trip curve to see where the load may fall if the curve were to be derated to 50degC. In most cases it's not an issue and a stock 40degC breaker can be used without a problem.
 
Even more stuff

Even more stuff

Q: So, do you make breakers with a coil that responds only to current and are less sensitive to ambient temp?

A: There are MAGNETIC ONLY motor circuit protectors that do not have a thermal element, for providing instantaneous only protection in motor applications. However, a full overcurrent device (e.g.,circuit breaker) MUST be upstream and/or in combination with these "magnetic only" motor circuit protectors because there is no thermal protection.
 
There used to breakers that were ambient compensating. These breakers will continual correct within a given range for ambient temperatures. Again, non-UL. Westinghouse made them that usually had an ?A? suffix.
A simple physically thermal magnetic breaker has a bimetallic element that responses to the heating affect of current flowing through the breaker. As current increases so does the heating. The thermal element will eventually bend far enough to hit the trip bar tripping the breaker. With a breaker that is calibrated in a 40degC ambient (ambient compensated) the breaker should carry its rated current continually with tripping.
As the current rises above the continuos current rating the breaker will trip in a given amount of time the greater the over current is the faster it will trip.

An ambient compensating breaker has a dual bimetallic element. One bimetallic element continually adjusts the thermal element to compensate for the ambient temperature with the intent on keeping the trip curve relatively constant even when the ambient changes.

It must be emphasized that this sound great by one must remember that breakers protect cable. A breaker that does this funny dance ignores its responsibility in protecting the cable.
 
This is getting interesting

This is getting interesting

And confusing.
Let's say you have a motor or compressor with all of its start-up kinks and quirks connected to a breaker through a cable.
Does the NEC prevent a conflict between the motor requirements and the cable requirements so that there is always some breaker somewhere that keeps both "components" happy at the same time?
Or maybe the motor has its own local and customized breaker, like in a Disposall?

While we're at it, are there on-line obsolete versions of the code that can be electronically word-searched, for free? I can learn a lot from any version of the code and this type of word search is better than any hard-copy index.
 
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