I disagree, the panel label will show if and where the tandems can be used. The 40 circuit panels I have seen and installed do not allow tandems. The mounting rails will not allow the use of CTL (circuit tandem limiting) breakers. Use of non-CTL breakers are listed for replacement use only.
A panel like a QO200M3040 takes 30 full size breakers but can use 10 tandems to makeup the 40 circuits. The devil is in the details.
On a side note why use a breaker than is more than double the cost over a single?
Originally Posted by hpp58
The question was "how many double poll breakers could fit?"
Tandems are not double poll breakers.
Right, I think there is confusion here.
Jim, I agree with you IF it were about tandems. The question was about double pole breakers for a 240v circuit.