ATPMSD
Active Member
You misunderstood. The Tandem breaker is to make space so a dual-pole breaker can be installed.You cant just replace a single breaker with a tandem. They will both pull from the same leg. You need to replace two single breakers with a quad. I did this in my shop. The quad pulls from 2 legs and has a single tied 220 breaker in the #2 and 3 spot.
All the counter arguments against this assume its your house and that you can take the time to modify the breaker box and outlets. The point of a tool like this is allow tapping where proper V/A is just not available.