Is the # of tandem breakers limited by NEC?

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rokefuller

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I had it in my head that one could only install 4 tandem breakers in a panel and those had to be on the bottom spaces. I looked in the NEC in the Overcurrent, and Panel and Switchboard sections and could not find a reference to verify what I had been taught. Is this currently, or was this at one time an NEC standard? Code references appreciated. Thank You!
 
The number of tandem breakers is limited by the number of circuits for which the panel is rated. For example, a Square D QO13040 panel is a single phase panel with 30 spaces rated for 40 circuits. Therefore you can have 10 tandem breakers with 2 circuits each and 20 positions with 1 circuit each.

The panels are usually provided with interlock devices to limit where the tandem breakers can be installed. Some of the old breakers will fit anywhere. I have some 40 year old tandem QOT breakers in my panel that will fit anywhere.
 
There are even some panels that can be filled completely with tandem breakers such as the Square D QO612L100S

Bob NH said:
I have some 40 year old tandem QOT breakers in my panel that will fit anywhere.
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The QOTxxxx breaker can only be mounted in CTL (circuit limiting) panels. It is the non-CTL QOxxxx that is usually mis-applied by being installed in panels not designed for use with tandem breakers.
 
there are many panels that are 20-40 rated also twenty "piggy backs" that will make fourty circuits, it makes for one crowded box if your not careful, or even if you are.Nothing I hate more then trying to work in a panel with wires jammed every were in a knot. Oh well, I can't think of any other job I would rather be doing.Being an electrician is a great job.
 
acrwc10 said:
there are many panels that are 20-40 rated also twenty "piggy backs" that will make fourty circuits, it makes for one crowded box if your not careful, or even if you are.Nothing I hate more then trying to work in a panel with wires jammed every were in a knot. Oh well, I can't think of any other job I would rather be doing.Being an electrician is a great job.
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A panel jammed up in a knot is more likely due to the installer and not the panel. Even a 20-40 panel can be neat if installed correctly.
 
I know that this doesn't address the question raised, but this is a good time to mention the shared neutral issue to anyone reading that hasn't noticed that both sides of the tandem share the same phase (or same side of the phase in a center tapped single phase house service).

Don't land hots from the same multiwire homerun on the same tandem or you can get doubled currents on your neutral. . I see homeowners make this dangerous mistake quite frequently and ELCs doing it occasionally.

David
 
I use GE panels, mostly, and they have a tandem that PULLS from 2 PHASES.

This can be good for adding a 220 ckt
(by clipping the handles together properly).
 
dnem said:
Don't land hots from the same multiwire homerun on the same tandem or you can get doubled currents on your neutral. . I see homeowners make this dangerous mistake quite frequently and ELCs doing it occasionally.
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I've seen it from experienced help before too. Kinda stops you in your tracks when that sort of thing happens.
eek.gif
 
dnem said:
Don't land hots from the same multiwire homerun on the same tandem or you can get doubled currents on your neutral.
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Good point, and thanks for mentioning it. I had not considered that before. But then, I don't think I would intentionally design a system that included tandem breakers.
 
rokefuller said:
I had it in my head that one could only install 4 tandem breakers in a panel and those had to be on the bottom spaces.
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You won't find this in the NEC, past or present.

The requirements, that control, first, whether tandems can be installed at all, and, second, on which poles and how many poles, are published by the manufacturer.

Careful examination of a panel's bus diagram (pasted inside, or on, the panel, if present) will tell a lot.
 
Tandem/Twin/Mini Breakers

Tandem/Twin/Mini Breakers

GE also makes a 3-phase 120Y208 volt panel that accepts a whole bunch of mini circuit breakers resulting in AABBCC phasing if 6 minis are installed together. Hopefully, the two multiwire branch circuits are wired ABCNG ABCNG and not AABNG BCCNG.

The last time I deliberately installed a panel with some tandem breakers was a SquareD Homeline panel where we wanted to get 36 branch breaker poles in a reasonable amount of vertical space for an appliance testing area. We wanted enough vertical room left on a 48x47 inch mounting board and line up the new board with the existing board and old panel such as to make the old panel into a junction box. A future upgrade will be from a 100 amp temporary feed to two 200 amp feeds and a second panel off of a 600 amp single phase service.

Mike Cole

Oh yeah, I passed my Ohio Electrical Contractor exams on 30 August 2006 but have yet to raise enough money for the insurance that I need to get my license issued.
 
acrwc10 said:
there are many panels that are 20-40 rated also twenty "piggy backs" that will make fourty circuits, it makes for one crowded box if your not careful, or even if you are.Nothing I hate more then trying to work in a panel with wires jammed every were in a knot. Oh well, I can't think of any other job I would rather be doing.Being an electrician is a great job.
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Why does this sound less than enthusiastic?

The guy I've been working with here in Austin is another neat-freak. I must say that I'd rather work with an electrician who likes nice pretty wiring than someone who runs crap hither and yon.

I'm thinking someone needs to invent wire holders for the insides of panels the same as spark plug wire holders for cars. I mean, real cars. The kind with 8 cylinders. ;) Something to keep all those d@mned wires out of the way of each other ...
 
dcspector said:
Julie it is called....I care about my workmanship and........"Zip Ties"
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Zip tying conductors together doesn't get into any kind of temperature derating issue? Or are you putting the zip ties somewhere else?
 
celtic said:
Pics?

Of what?
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Zip ties holding wires together in a panel? I've never seen it done.

I showed you my beer, now show me one of your panels. I think that's a fair trade :)
 
tallgirl said:
I showed you my beer, now show me one of your panels. I think that's a fair trade :)
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LOL

Ok...lemme search my comp. for a "fine example".

EDIT:
Bad news.
The pictures I "had" were lost when the HD crashed in 8/04 (along with all the pics I had from '03 - '04)


I *could* remove my panel cover and take a shot of it.....
 
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