single pole double circuit breaker

[nelsonba]

Are these legal under NEC?

[BrianJohn]

Does it have a UL or equivalent seal/sticker, if so yes.

[Bob NH]

It appears that you are talking about what is often called a "Tandem" breaker that connects to one side of the load center, and contains two separate circuit breaker devices with two handles.

The only risk would be if someone incorrectly connected both hot wires of what was intended to be a multiwire branch circuit, with only one neutral, to both terminals of a tandem breaker.

[Igor]

See http://www.ul.com/regulators/novdec2002.pdf for UL's position on the use of tandem breakers.

The 42-circuit limit, which dates back to the 1930's when flammable rubber-insulated wire was used, is going to be removed in the 2008 edition of the NEC.