OK I understand the difference between CTL and Non-CTL. I am becoming confused. I had a licensed electrician give me a quote to install a 100 amp 2 pole breaker into my 40 space panel. But he would have to use tandem breakers in order to get the 2 pole breaker to fit. When I reviewed the panel, it states the breakers which can be used and BR breakers are acceptable. However since this is a ctl panel and all the slots (40, but only 39 poles) are used, he would have to get the tandem breakers which the only ones I see can fit are non-ctl. When I question him on non-ctl vs ctl he did not understand. I have queried several electricians and I am getting the same answer. They will use tandem breakers and place the 2 pole 100 amp in the remaining open slot. This would put my panel at 41 poles, below the 42 limit.
What can be my other options if I cannot use the tandem breakers? I believe they are install a sub panel, but due to the panel location I would have to tear out the dry wall, cut through double header 2 x 4's or I guess I can install a 320 meter base, but I am not sure the service wire will handle it. Can I place a sub panel on the outside of the house? I do not want to do this, but I cannot come up with other options. All the electricians state they will install the tandems.
IF I install a sub panel do I have to use conduit in the garage walls? I can go up inside the wall to the attic and come down the other wall and install the sub panel. Also if I do this can I run wire from the sub panel through the main panel to the outside wall where I would then use schedule 80 PVC to run underground. From your statements I am not to confident in the electricians I have been getting quotes from. I believe it is because I live in the country where there are no city codes. Thank you for your assistance.

The total will be 41 circuits, the max is 42, not sure what the problem is. As you state the panel will be just 1 pole under the max which is fine.

A 40 circuit panel should be able to take two more breakers, using tandems to allow a total of 42, which is allowed.

BR is the frame, or that makes designation or model number, which is Eaton/Westinghouse/Cutler Hammer.

But is anyone wants to add more than 42, then the panel is CTL rated, and should not be able to add more. If any electrician does not know why, direct them to NEC Section 408.15.

CTL is a UL listing not a NEC listing.

Hope this helps, ask more question if not.

Hope this helps, ask more question if not.
Hi tk,
Is there a possibility that the panelboard can be scoped out for general lighting load distribution for paralleling two low demand general BC's together into one panel breaker (same amp size) and gaining slot space for the new dp breaker? Wirenut parallel hookup in the enclosure is allowed per NEC as I have experienced in past remods. Nm

That is a possibility, to double up two lightly loaded lighting circuits. This can be done by splicing the two branch circuit wires with a pigtail to connect both to one breaker.