I came across this today:
Thanks John…great article shared for the knowledge to help others by a founding member of the Distinguished Inspector Society…
Good find thanks… John
Thanks, John…good info.
Just to note that this is region specific.
Tandem or mini breakers not allowed in Chicago as fire hazards.
They are used because the panel will not accept any more breakers meaning you might be overloading them.
One of the comments below the article explains it some what…
heelectrici
Mar 2, 12
11:13 pm
A common problem with tandem breakers is one that most people do not even realize. A tandem breaker is installed on a single phase, so if a common neutral is being shared with the circuit, the result is an overload on the neutral. As a result, the neutral wire and busbar are overloaded.
This frequently happens also on regular breakers .
Some people should leave electricity to the pros.
While the neutral would be overloaded, it would have the same effect on the neutral bar as two circuits on single pole breakers.
Not sure where this came from as I haven’t looked at the article, but a shared neutral is not allowed for use on tandem breakers, just for this reason.
If you have someone installing tandems with shared neutrals, what’s to say they’re not installing other circuits improperly?
It was a comment from an electrician.
None the less the box is a certain size and adding more branch circuits by cramming them in might be inviting trouble.
Here they are simply against code and as a Home Inspector my job is not to calculate loads .
Yeah ,yeah can be done properly but properly is a box made to hold them rather than a workaround solution.
So, in Chicago, tandems are allowed if the panel is designed to hold them?
Thanks John, nice read. Glad you posted it, helping our HI bros!
Never said that.
The last sentence in your previous post hinted that. This is why I Ask.
Tandems are allowed in this part of the State, when installed according to manufacturer.
I thought that is exactly what the article indicated. Did you read it?
A good article and it points out that when installed properly there is no real safety issue with the use of tandem breakers.
Adding 15 and 20 amp circuits then doubling the amperage is not a great idea and yes I skimmed through the article however what caught my attention first was naturally the very first paragraph.
Confusion abounds over the use of tandem circuit breakers in panelboards, even among electricians and electrical inspectors.
Just glad they are not allowed in my main service area.
Probably cause of this. 
If the bus bar is designed for it, how could it be anymore dangerous?
If you are not going to read and understand the article why would you comment?
The key is when installed properly.
Same could be said for aluminum branch wiring.
Still suggest one checks for local codes.
My home yesterday (inspected) was called out by the village for mini breakers and now must be replaced along with the entire panel or a sub panel installed as there are no more spaces left.