Confused on using tandem breaker in Murray 200A/ 40 ckt panel

I needed to add a circuit to my Murray 200A panel. The panel was installed 10 years ago. I purchased a Murray twin breaker from Lowes, and I installed in the panel with no problem.
Then I did some reading that most 40 ckt panels will not accept a twin breaker. And then I read the inside label of my panel, it did not indicate any twin breakers could be used
So now I'm confused. How was this twin breaker able to be installed? I thought these panels had provisions or interlocks that prevented these breakers form being installed?
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On Sunday, September 28, 2014 9:18:10 AM UTC-4, Mikepier wrote:

lets see you needed a breaker installed a twin and it works?
then dont worry about it:)
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"bob haller"

Sounds to me like a dumb-assed con-artist ins.co. thief said 'you can't do that, it might cost us money' !
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I thought I was going to make a quick paraphrasing effort and look brilliant, but just read this yourself!
http://www.structuretech1.com/2012/02/tandem-circuit-breakers/
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On 09/28/2014 9:15 AM, Pico Rico wrote: ...

Nice link, thanks! Wasn't aware of the recent changes in NEC in this area.
BTW, I've never seen the Square D horizontally-spaced tandem style...
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On 9/28/2014 10:15 AM, Pico Rico wrote:

Thank you. I learned a lot.
. Christopher A. Young Learn about Jesus www.lds.org .
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On Sun, 28 Sep 2014 07:15:08 -0700, "Pico Rico"

The article does point out that the NEC removed the 42 pole limit on panelboards so these are a little murkier. When the panel was listed adding a tandem breaker might have exceeded the 42 limit, now it doesn't. I would bet that there are 2 slots in that 40 breaker panel where CTL breakers are allowed. (probably right next to the main)
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That is an old style that are fairly hard to find these days but they did allow using handle ties to get a tandem 240 v pair. It is not legal to do that now. Breakers on 240v circuits require internal trip for both poles. You could use the handle tied breakers on a multiwire circuit. (AKA Edison, Shared neutral etc)
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Thanks for the article. So if I'm reading it correctly, tandem breakers can be used in non-CTL panels?
How do I know if my Murray 200A panel is non-CTL? I don't see anywhere on the label. The model number is LC4040B1200. Attached is the label. http://www.homedepot.com/catalog/pdfImages/4d/4d7b43bf-9745-4a27-a8a2-61055abf9d39.pdf
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On 09/28/2014 5:25 PM, Mikepier wrote:

If the panel indicates so, yes, in those locations.

If it doesn't say it is, it isn't... :)
And, the pictures at the top indicate it doesn't allow _any_ tandem breakers (they're no double lines in any locations). See how the samples in the previous link show where they are/aren't allowed...
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On Sunday, September 28, 2014 7:21:11 PM UTC-4, dpb wrote:

Confusing to say the least. Even though its not shown on the label, I thoug ht the article says something to the effect that if the panel is not CTL ra ted ( which it does not appear to be because I do not see anything on the l abel saying "MAX circuits 42'), then I was under the assumption it could be used.
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On Sunday, September 28, 2014 6:25:50 PM UTC-4, Mikepier wrote:

*The catalog number says it all. 40 spaces, 40 circuits, period. One thin g that I noticed on that label is the notation indicating the location wher e a backfed circuit breaker must go in slots #1 and #3. This may limit the use of third party generator interlock kits which tend to be located in th e #2 and #4 slots. Most likely Murray (Siemens) has their own interlock ki t for this panel. Just an observation. Sorry to digress.
John Grabowski http://www.MrElectrician.TV
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On Sun, 28 Sep 2014 15:25:50 -0700 (PDT), Mikepier

Unfortunately that panel label seems to preclude your tandem breaker.
The type "MT" (tandem) is not on the list of approved breaker types. It probably won't burn your house down but it is not legal.
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That would appear to be the case. Ok no big deal. I actually used a twin breaker to re-arrange some breakers in my panel to accommodate putting a 30A backfed generator inlet on the top right.
I actually have plenty of spaces left in my panel, but one of the 15A circuits in the panel would not reach to the new spot of the breaker, so to avoid extending it with another wire and wire nut, I just used a twin.
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On Mon, 29 Sep 2014 02:57:26 -0700 (PDT), Mikepier

In spite of the urban legends, there is nothing wrong with splicing a little pigtail on the wire that is too short so you can get to the breaker you moved.
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In typed:

Interesting thread. I never knew that there technically could be a legal or other issue when using a tandem breaker in a panel. I just assumed that if it fit in the slot and it worked, it was okay to use.
But, since you have plenty of extra spaces, and you can put in a regular breaker by just using a wire nut inside the panel extending the existing wire, I think that I would have chosen that option rather than buying and putting in a tandem breaker. That would eliminate the whole question or issue of whether using a tandem breaker in that panel is proper or legal etc.
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