If your basement has a bar, you could pour a double tap beer while your electrical box nearby may have a double tap breaker. You can enjoy the beer, but you should fix the breaker.
Do professional electricians use a double tap? Definitely not. But amateurs often make this mistake.
The electrical breakers in your main panel usually are designed to hold one wire. Some special breakers can hold more than one wire, but the wires must be the same size.
Take a look at the illustration of an electrical circuit breaker connected to two wires – a double tap. This is a problem, because the clamp is designed to squeeze down on one wire to make a secure connection. Here we have wires of different diameters (different amperage ratings), and the smaller wire is loose.
A loose connection can cause arcing. Then the wire and the breaker can overheat. This dangerous situation must be corrected by an electrician. If professional electricians installed your electrical wiring, you won’t find this situation. If amateurs have been working in the main panel, your system could have this problem.