Add tandem breakers to expand the available circuits in your fuse box (more accurately called a breaker box). But be careful. Only certain breaker slots will accept them.
By the DIY experts of The Family Handyman Magazine
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Add breaker circuits to your breaker box
Full size and tandem circuit breakers
Certain slots in electrical panels will accept tandem breakers or a split breaker, but not all slots.
When you want to add more circuits to your fuse box (breaker box), keep in mind that not all slots in a panel will accept tandem breakers (or a split breaker), and each panel will accept only a certain number. To find out where the tandem slots are located and how many you can install, first see if the information is on the label inside the main electrical panel. If it’s not, you’ll have to call the manufacturer’s help line and supply the model number. That’s the only way to get the answer.