Tandem Circuit Breakers — What They Are and When to Use Them

What Is a Tandem Breaker?

A tandem breaker is a single-slot breaker that contains two independent circuit breakers side by side. Each side has its own trip mechanism and handles two separate circuits. They are the same height as a standard breaker but half the width of a 2-pole breaker.

When Can You Use Tandem Breakers?

Not all panels accept tandem breakers, and those that do may only accept them in specific slots. The panel's load center directory (usually on the inside of the panel door) will indicate which slots are 'tandem-capable' or 'CTL' (Circuit Total Limiting) slots.

The NEC limits the total number of circuits in a panel based on its rating. A 200-amp panel rated for 40 circuits cannot have more than 40 circuits installed, even if you use tandem breakers.

How to Find Compatible Tandem Breakers

Tandem breakers must be the same brand as the panel and specifically listed for tandem use in that panel. Common tandem breakers:

Square D QO: QO2020 (2×20A), QO1515 (2×15A) Square D HOM: HOM2020 (2×20A) Eaton BR: BR2020 (2×20A) Siemens: QT1515 (2×15A), QT2020 (2×20A) GE: THQP115 (1×15A, half-size)

Always verify the specific part number is listed for your panel model.

Limitations of Tandem Breakers

Tandem breakers are only available as 1-pole (120V) units — you cannot get a tandem 2-pole (240V) breaker. They are limited to 15 or 20 amps in most residential applications. They cannot be AFCI or GFCI in most configurations (though some manufacturers offer tandem AFCI/GFCI breakers for specific panels).

When a Subpanel Is the Better Answer

If your panel is truly full and you need more circuits, adding a subpanel is often a better long-term solution than filling every slot with tandem breakers. A subpanel gives you a clean, organized expansion with room for future growth.