Several arc fault breakers in panels

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I think that some here may be rushing to an incorrect conclusion... that being the temperatures that have been mentioned are going to cause or create some catastrophic condition within the panel enclosure.


Take a close look at the temperature ratings of conductors at the top of Table 310.16. You will see that the temperatures for the conductors are higher than most usually comprehend. These temps are also relative to some equipment.

Also, to mention is that the manufacturers have already tested the existing Arc Fault CBs with the existing electronics at the temps created within the Arc Fault CB and know that the standard temps are elevated.

If one was to load a 20 amp circuit up to its full limit, the temperature of a standard circuit breaker would be well over 125F, I cannot remember the exact temperature. There is a formula to come to a close number and I cannot find it. Circuit breakers under load get warm - hot and a lot of people think something may be wrong...not always.

Last, the manufacturers have all redesigned the electronics in their newer Arc Fault CBs and the operating temperature will be reduced. I have not heard yet of one failure of Arc Fault CBs due to temperature issues.

I would not call the fire department just yet ;) .
 
The August, 2004, bulletin titled AFCIs and Heat Rise has the following:
On residential circuit breakers, the temperature rise of this terminal must be 50?C or less above ambient when carrying rated current, or 65?C or less above ambient in an enclosure.
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65? C + 20? C (ambient) = 85? C

So this is saying a 75? C terminal can get as hot as 85? C ? The bulletin seems to be sourcing that statement to UL 489 and UL 1699.
 
Does any one know how much money per year it costs to run an AFCI breaker?? Do they have a wattage rating ? They do get pretty warm even when there is no load .....Just curious.
 
Thank you Pierre. A field representative from Cutler Hammer is visiting the site in question to run some infrared testing for hot spots, ambient temperatures, peak temperatures, etc. Once that is complete, maybe we'll have some info that we can all use. The newer breakers WILL operate at a lower temperature (per the industry comments) and that will put a few more minds at ease.
It appears that the highest heat is located within the breakers themselve, but the manufacturer's rep that I spoke with assured me that the terminal ratings would not be exceeded. The only problem I have with that is that the highest terminal rating with these breakers (in the catalog) is 75C, which is 167F. Right now the ambient temperature in the panels (at the upper portion) is around 140F (+/-), and that has us thinking a little about the terminal ratings as well as the insulation ratings of the conductors.
I'm sure that this will work itself out to everyone's satisfaction. I do not believe that it is so much a fire safety issue as it is a performance/life expectancy issue.
 
al hildenbrand said:
65? C + 20? C (ambient) = 85? C
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The 20? C ambient is outside air ambient, the ambient outside the enclosure.

Add the additional heat source of the AFCI electronics to the bimetal trips and let's say there is an enclosure internal ambient temp rise of 20 C? that puts the breaker terminal at 105? C.
 
earshavewalls said:
I do not believe that it is so much a fire safety issue as it is a performance/life expectancy issue.
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Given that the heat concentrates at the connections and internal breaker contacts, the end-of-life scenarios will most likely include the catastrophic failure of those connections / contacts with load current sustained series arcs, that the AFCI electronics, we are assured by UL, will NOT detect because the arc current is not exceeding the 50 to 70 amps trigger threshhold.

That's assuming the electronics are, in fact, still viable at the end of this heat degradation cycle.
 
al hildenbrand said:
Given that the heat concentrates at the connections and internal breaker contacts, the end-of-life scenarios will most likely include the catastrophic failure of those connections / contacts with load current sustained series arcs, that the AFCI electronics, we are assured by UL, will NOT detect because the arc current is not exceeding the 50 to 70 amps trigger threshhold.

That's assuming the electronics are, in fact, still viable at the end of this heat degradation cycle.
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Al
Where did you get that information from?
 
I tried to post photos of two panels side by side that are 42 circuit panels with 36 spaces, all bunched together, no spacing, full of AFCI breakers.........but the file is too large to get on here.
Even if they separate the breakers as best as they can, it still would have several grouped together.
A Cutler Hammer representative is planning a trip out to take some measurements and other readings on what is going on. Hopefully this will help the development of these things so that we won't have this problem in the future. I believe it was definitely a design flaw here......but that's evolution.
(Design flaw on both the manufacture and the engineering of this system)
 
M. D. said:
Does any one know how much money per year it costs to run an AFCI breaker?? Do they have a wattage rating ? They do get pretty warm even when there is no load .....Just curious.
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Hmm. Given this information, I bet I could make a statistical argument that AFCI breakers will _kill_ more people than they save.

The argument would go something like this:
AFCI use electricity which a homeowner would not otherwise choose to use. This will increase the over-all power consumption of the home, leading to greater emissions from power plants. These increased emissions will contribute to early mortality due to illness such as emphysema. Using estimates of the early mortality due to increased power usage, versus the reduced mortality from prevented fires, there is a net loss of xxx person days of life.

Of course, I don't actually know the numbers, and even if the numbers were known, it would arguably be better for lots of people to _statistically_ lose a couple of days of life than to have a few people lose many years, and perhaps more people would be saved than killed....

-Jon
 
ptonsparky said:
:cool: Yes, by all means put the afci on every other breaker space, make sure to put them directly accross from each other so the panel is prettier.
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That means that the entire panel-ful would be on one phase.
 
earshavewalls said:
(Design flaw on both the manufacture and the engineering of this system)
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Agreed!

It might not be possible to do this legally, or even at all, but could small fans be installed, like in electronics or some machinery I have seen?
 
al hildenbrand said:
Add the additional heat source of the AFCI electronics to the bimetal trips and let's say there is an enclosure internal ambient temp rise of 20 C? that puts the breaker terminal at 105? C.
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Keep in mind that terminal temperature ratings are concerned with the wire heating the terminal, not the other way around.
 
celtic said:
Is that an issue with AFCI's?
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No, but I wouldn't want to wire panels that way. To utilize transformers efficiently, we'd have to assign homes alternate phase use. :rolleyes:
 
earshavewalls said:
I tried to post photos of two panels side by side that are 42 circuit panels with 36 spaces, all bunched together, no spacing, full of AFCI breakers.........but the file is too large to get on here.
Even if they separate the breakers as best as they can, it still would have several grouped together.
A Cutler Hammer representative is planning a trip out to take some measurements and other readings on what is going on. Hopefully this will help the development of these things so that we won't have this problem in the future. I believe it was definitely a design flaw here......but that's evolution.
(Design flaw on both the manufacture and the engineering of this system)
Click to expand...
Two of the panels in question http://i137.photobucket.com/albums/q217/jhenderson6/afci.jpgs
 
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