Burnt Outlet

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On 3/2/2014 12:55 PM, Robert Green wrote:

I agree with 20 and 100. M means it has a main breaker. (As in your link below.)
I don't know what BW is either. Need a real old catalog.
I would read "20" as not allowing tandem breakers. "2024" would allow tandems in 4 positions. But it is an old catalog number.
Seems like UL had maximum number of poles depending on the panel rating. I think a 100A panel had a max of 20 poles and 200A had a max of 40 or 42 poles. That makes it harder to overload a panel, but doesn't work so good if you don't have much on each circuit (so you need more circuits). SquareD has panels with a lot more poles ("circuits") than that now.

SquareD class CTL tandem breakers have the usual horizontal clip at the busbar end. At the gutter rail end they have what you describe as a claw, which fits into a slot in the gutter rail. The slot is only present at the positions where tandem breakers are allowed.
Your farnell link has a crappy picture for a Homeline panel on page 9 of your link. A better picture is http://www.circuitbreakersuperstore.com/qot1515_8_2_5862.html where the gutter rail claw can be seen.
Regular breakers just have a clip at the gutter rail end, as with your original breakers.

The difference is only in the gutter rail.

Yes.
I don't entirely agree with the limit on circuits. If I watch the connected load I might install tandems where you are not supposed to.
I think one reason for the limit is to limit the heat produced in the panel. Heat can cause a breaker to trip at a lower current. Would seem like a 100A panel would only make 100A of heat no matter how many breakers.
There is, in general, a limitation for fuses and circuit breakers of 80% for "continuous" loads, which are loads that are on for 3 hours or more. My understanding is this is based on panel heat, and the breaker may trip at less than 100% if the load is on for more than 3 hours.
An exposed 20A breaker or fuse by itself is supposed to hold at 20A forever.
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I've found that publications printed before the internet often never make their way to the net. I don't see myself spending too much time looking for the meaning of BW.

Those tandem breakers fit just fine <g>. I looked at the box again and the rails are continous without interruption or anything that looks like special slotting meant to accept tandems only in one spot.

It would be nice to upgrade to a newer panel but it wouldn't be cost effective. This place has to be "shelled" when I am through with it. Boy will my heirs be disappointed. (-:

No slots in my gutter rail. All the same from top to bottom but at least now I know why they changed the clamping mechanism. Boy was I certain when I got them home that they were the wrong style breakers even though I had religiously copied down the breaker information from the one I had pulled. I also discovered that the previous owner had replaced 15A breakers with 20A ones, which I based on the fact that the same gauge wires were feeding both sizes of breaker. I replaced those 20A units with 15A ones, just to be on the safe side.
I figured wiring from 1940 was not likely to be 20A capable but the idiots before me apparently found the kitchen circuits tripped less frequently with the larger capacity breaker. Sadly, you could see that the 20A breaker feed wires had evidence of overheating. That's what led me to add the tandem/dual skinnies and run new wires to the kitchen and workshop areas.

Either kind of breaker fits into any slot on the breaker panel I have. I saw a printer's mark on one label in the box that said 1961. Of course, there's no telling if that's related to the date the panel was installed. But based on the history of this house that I know about, it's entirely possible the panel is that old. I know at one point it was a screw fuse panel because I found a bunch of fuses directly below the panel area when I pulled the old paneling off the basement.

Then I don't have a CTL panel.

I think the offloading of old, cloth-covered wiring to newer 12/2 NM justified the use of tandems in my case. It has to be safer using new wiring than muddling through with the old crap.

There are some interesting charts here about temperature, load and other factors relating to breakers and how they trip and when.
http://static.schneider-electric.us/docs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0730CT9801R108.pdf

I saw something (not especially credible - one of those "ask me" sorts of sites) that said because of the heat generated by the electronics in AFCI breakers, they had to be mounted away from each other. I also read manufacturer info that said that heat generation was taken into account. That's where I also saw something about the NEC required that instrument controls that a user had to operate with fingers not be over 140F. That seems a little high.
--
Bobby G.



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On 3/6/2014 10:57 AM, Robert Green wrote:

Then I presume you used non-CTL tandem breakers.

You can't tell that from the rail. The panel could just not allow any tandem breakers.
Sounds like from the date you found it is not a CTL panel and it is kosher to use non-CTL tandem breakers.
I am not entirely convinced that is a problem anyway. If you have a 100A panel seems like you would only get '100A of heat' no matter how many circuits/poles there are. You would have to watch how much load you connect so you don't actually overload the panel.
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I used what Home Depot had on the shelves that matched the QO designation and it was approved by the AHJ. Dual skinnies/tandems are a pretty popular item in this development of houses built to house the army of workers that descended on DC at the beginning of WWII. Fortunately with CFLs and more efficient motors the average load for such items has decreased substantially (although the number of plug in chargers and appliances has increased geometrically). I assume when I ultimately switch to LEDs the overall load will be reduced again.

Tell that to the four that are in there now! (-:

That date's not conclusive. They could have been using the same label for 20 years. There must be some other date markings inside the box. Reading all the details is getting to be like reading "War and Peace" - very arduous.

I do. A long time ago I installed two Hall effect sensors on the incoming feeds. For days I was calibrating them with various space heater loads (this was the springtime and it drove my wife a little crazy having me run space heaters with the windows open. She's a frugal New Englander). Those sensors feed into my HomeVision home automation controller's analog inputs. From there I can roughly gauge the total load at any one time and it very rarely exceeds 50A, and only then when it's very cold which self-limits the overheating panel problem to some extent.
--
Bobby G.




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circuit limit number is to protect breaker box from being overfilled. just like te limit of the number of wires in any box
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My panel seems to be in an oversize box - thank God - because there's at least 8" of empty space in the box below where the gutter rails end.
--
Bobby G.



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