tandem breakers

[netcom45850]

I could not find anything in the NEC on this
Do tandem breakers count for 1 or 2 spaces in a panel???
the situation I Have is a 200A 42 space panel all spaces full of sp20a breakers, so If I add a tandem does this violate the NEC rule of a 200A panel can have no more than 42 breakers????

 

[templdl]

Re: tandem breakers

You can only use tandem breakers if the panel is listed for their use. A "space" is normally a full size device such as a 1" or 3/4" full size 1 pole breaker. If tandem breakers are allow the panel will not only list the number of spaces but the number of poles which may be greater than spaces. A panel that has 20 spaces may also have 24 poles. In other words the panel will accept either 20 full size brekaers or up to 16 full size breakers and 4 tandem breakers. The tandem breakers are normally allowed, or able to be installed in last two spaces on each side of the panel on the other end from the main breaker.

 

[luke warmwater]

Re: tandem breakers

I suspect this is a Cutler Hammer 200a. 42space. If so, then it is only listed for 42 spaces, none of which is rated for tandems. Now look at 408.15

 

[bphgravity]

Re: tandem breakers

It is my opinion that Tandem breakers count as one space but 2 OCD. The code does not specify maximum spaces allowed, but maximum OCD allowed. A 42 space panel should not accept a tandem breaker. Any panel under 42 spaces may have postions that accept a tandem like a square D 30/40 panel.