Tandem Breakers

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VIC1958

Senior Member
This is a small commercial building, light electrica load. Panel is a older 200 amp model. I have not personally inspected it. Contractor brought in a picture of it and it showed 5 tandem breakers. I cant find anything in the 2005 code that addresses this issue. Section 408.35 says no more than 42 per cabinet ( this cabinet is smaller than that) it also states that the panel board be provided with physical means to prevent the installatiion of more overcurrent devices that which the panel board was designed and rated for. Need help on that last part.
 
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btharmy

Senior Member
Location
Indiana
All panels that allow tandems that I have ever worked on make provisions in the bottom spaces. So, if it is a 30/42 panel then the bottom 6 spaces on each side will allow tandems. This is usually obvious by the notch in the buss bar corresponding to those spaces. If the tandems are located at the bottom, you're probably good. If at the top, look a little closer for "modified" breakers.
 
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hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
I'm not really sure exactly when "CTL" panels and tandems were introduce to the manufactures, but I think I remember starting to see them in the late "80's" A CTL rated panel will have a slash breaker space rating such as a 30/40 where the bottom ten spaces can be tandems, or a 12/24 in which all spaces will allow a CTL tandem, prier to this tandems didn't have any restrictions other then the 42 space limitation in the NEC and by UL, after CTL panels came out manufactures started making a tandem called a NC, and stated on it side: "Not for use in CTL installations, For replacement only" or something like that. These were allowed by UL to be installed in the older smaller panels that allowed circuits to be added, but are not allowed in the newer CTL panels as they allow a person to circumvent the rejection tabs that would other wise prevent more then the allowed breakers to be installed, so when looking at a panel, you must look for the slash space rating, and most of the time it is found in the panel model number.

Like was said it's not really in the NEC, it's in the listing and instruction for that panel that is listed by UL, this is the reason that the correct code to site is 110.3(B)
 
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RICK NAPIER

Senior Member
Location
New Jersey
Those "Not for use in CTL installations, For replacement only" are the best selling Home Depot breaker. I think they have sold more of them then there were panels originally made.
 
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jim dungar

Moderator
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Location
Wisconsin
Occupation
PE (Retired) - Power Systems
hurk27 said:
I'm not really sure exactly when "CTL" panels and tandems were introduce to the manufactures...
Click to expand...
You are 20 years too late.:cool:

I have a catalog dated 1966 referencing UL Listed Class CTL.
My 1960 catalog does not use the term CTL.
 
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stevrob4

Member
Tandem Circuit Breakers

Tandem Circuit Breakers

After reading every ones posts, I now haave question?

So now I can go to The Home Depot - store and buy a QO SD 20 amp. tandem
breaker, and place in my house with existing 12 space panel, installed back in 1984
and gain an extra 20 amp. circuit?:roll:
 
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