Sometimes there is a need to add a circuit breaker to a panel that is already full of breakers. This can be done by replacing one or more single pole breakers with tandem breakers. A tandem breaker takes up only one space in the panel but it provides two circuits. It will have two handles with two separate lugs for the wires to go.
These tandem breakers are not to be confused with a double pole breaker which would take up two spaces in the panel and provide 240 volts. If you are needing to add just one 120 volt circuit to the panel then replacing one regular single pole breaker with one tandem breaker will do the trick.
If you need to add a double pole breaker for a 240 volt circuit then you would need to remove 4 regular single pole breakers from the panel which would open up 4 spaces and then put two tandem breakers in two of the spaces. These two tandem breakers will have the four places you need to feed the four wires from the removed breakers plus you will have the two empty spaces that you need for the new double pole breakers that you are adding.
For example, the four single pole breakers take up four spaces in the panel. Two tandem breaker only take up two spaces but give you the capability to re-feed all four wires from just two spaces in the panel, leaving you two open spaces for the new breaker.
There are a couple of things that you will need to verify before doing this. You must check the amperage rating for each single pole breaker that will be removed and make sure that the tandem breaker ratings match back up to each circuit. If all four breakers are rated at 20 amps each then you would need two tandem 20/20 breakers. You can also look at the wire size. #12 awg wire would go on a 20 amp breaker and #14 awg wire would need a 15 amp breaker.
If two were 20 amp and two were 15 amp breakers then you could get 1 tandem 20/20 and 1 tandem 15/15, or you could get two tandem 15/20 breakers.
The second thing to verify would be that all four romex cables are two conductor, in which they probably will be. You don’t want to have a 3 conductor cable that would be feeding two 120 volt circuits but using a common neutral and have those two hot wires from the same 3 conductor cable end up on a tandem breaker together. Two circuits that share a common neutral must be placed on opposite phases in the panel or you can overload the neutral.
See a Siemens Q2020 Tandem Breaker Here.
