Legal number of tandem circuit breakers in a panel

Last night I had a double-tapped breaker fail. Turns out the former owner put most of the overhead lighting, and the living room outlets, on these two taps.
It's a Cutler-Hammer box so the double-tap was legal.
The basement overheads started flickering as I was working, and soon went out. When I got to the panel, I could smell something was wrong, so I started feeling breakers for heat. Found a warm one that sizzled when I touched it.
Luckily I had purchased a tandem breaker (two separate circuits that fits in a single breaker slot) back when I took possession of the house.
Is there a limit on how many tandem breakers can be installed in a breaker panel? There are two now, and at least one other double-tapped circuit in the house.
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snipped-for-privacy@rochester.rr.com wrote: ...

Capacity/type will be on the panel label.
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I'm glad you posted this question.
I had a new box installed 2 weeks ago. Siemens made in Canada Box with Siemens made in USA breakers. I have 7 tandem breakers (thereby 14 circuits) on one side of the box. Siemens refers to this box as a 32/64 thereby implying that this box can handle 32 tandems i.e. 64 circuits.
The electrician's works was inspected and approved by the Electrical Safety Authority in Ontario.
Now these 7 tandems breakers are located on the side side of the panel as the following Electric dryer, electric stove, 230 V pool pump and central air circuit. I'm not concerned about the stove and dryer because we use gas but I throw that out there to see what people would think about all tandems and high draw circuits on one side of the box.
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On 10/11/2010 4:18 PM, The Henchman wrote:

i think the OP was referring to what i've heard called "minis". Two breakers that fit a single spot.
A "tandem" is two breakers in one that fit in two spots.
OP can correct as needed.
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Steve Barker
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IOW, a tandem breaker.

No, it's not. That's a double-pole breaker.
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The panel buss alternates both legs all the way down and on both sides, so it doesn't matter unless you installed them every other space, in which case they'd be on the same leg.

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The Henchman wrote:

Nice description.
Parts may be specific to the US.
A panel will have a limit on the number of 'poles' that are allowed - in the case above it is 64. It is the number of poles with which the panel was tested for listing. As several people have said, the label contains the information.
The NEC (and UL) require that tandem devices have a 'feature' that only allows them to be installed in panel positions where the manufacturer has a corresponding 'feature'. These are called class CTL panels and breakers (circuit limiting). For SquareD, the 'feature' on the breaker is a bar that has to fit into a slot in the mounting rail. In a 32/64 panel all the positions would have the 'feature'.
Tandem breakers are also made for old (non-CTL) panels and do not have the 'feature', so they fit in any position. I am sure no one would use them in a class CTL panel.
--
bud--

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On 10/11/2010 1:23 PM, snipped-for-privacy@rochester.rr.com wrote:

There are usually a limited number of spaces that will accept the tandem breakers indicated by different looking sections on the buss. The newer panels have spaces at the bottom made for tandem breakers. Do your tandem breakers have a different looking slot than the standard breakers? There is a label on the door of the breaker panel that will tell you what the maximum load rating is. If you look up the model number online you should be able to find out if it's rated for tandem breakers and how many. Quite often, another brand of breaker will fit when the OEM tandem wont.
TDD
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