Tandem circuit breakers are useful because they put two breakers into just one position on a circuit panel. They are approved for use by the National Electric Code for specific residential uses and have been tested for safety by Underwriters Laboratories. They must only serve standard 120 volt circuits and each circuit must have its own grounded conductor, commonly known as a neutral wire.

On the Other: Code Regulations

Some local codes have requirements that do not allow tandem circuit breakers. Generally, these are not safety issues. The NEC and Underwriters Laboratories have both certified tandem breakers as safe to use. However, local code enforcement authorities may argue that a circuit breaker panel box is made to accept a certain number of circuits and that number should not be exceeded, despite manufacturer, NEC and UL claims to the contrary.

Bottom Line

Tandem circuit breakers are safe to use for the purpose they were designed for. Generally they are not meant for new installations but are useful for expansion in some situations. Always check your local codes and building department before starting new projects.

Source:

Wiring Simplified 40th Edition; Richter, Schwan, Hartwell; 2002

More Information:

Tandem Breaker Use