On 2/26/2014 4:59 AM, Robert Green wrote:

I was mostly concerned at the time
that the inspector would disallow the dual skinnies because of the potential
to overload the panel.

Panels will have a rating something like 10/16. There are 10 full size
breaker positions and you can put 16 "poles" in it. A tandem breaker is
2 poles, so you could install up to 6 tandem breakers. The label should
tell you the rating.

The panel is tested with the maximum number of poles - 16 above - and UL
does not allow installing more poles than that. That is done by only
allowing tandem breakers in certain positions (6 in the example above).
The label will indicate which positions tandem breakers can be installed
in. In a 10/20 panel it is all positions. It may also be no positions. A
SquareD tandem breaker has a bar on the bottom that has to fit into a
slot through the gutter rail, which exists only in the positions where
tandem breakers are allowed. These are class CTL panels and breakers
(circuit limiting) and they have been around a long time.

The inspector wants to know that tandem breakers were installed in
positions where they are allowed.

There are also non-class CTL tandem breakers that can be installed in
any position - for older panels that are before CTL came out. I know no
one here would ever install one of them in a class CTL panel.