Siemens QP vs QT: Complete Comparison Guide
Siemens QP and QT breakers both fit in Siemens residential panels, but they serve different purposes. The QP is a standard full-size breaker occupying one panel slot per pole. The QT is a tandem (twin) breaker that fits two single-pole circuits into one panel slot — effectively doubling your panel capacity without upgrading the panel. Understanding when you can and cannot use QT tandems is critical for code compliance.
Siemens QP vs Siemens QT Comparison
| Feature | Siemens QP | Siemens QT |
|---|---|---|
| AIC Rating | 10,000A | 10,000A |
| Voltage | 120/240VAC | 120/240VAC |
| Circuits per Slot | 1 | 2 |
| Physical Width | 1 inch (standard) | 1 inch (two circuits) |
| Amp Range | 15A–50A (1P) | 15A–30A per circuit |
| 2-Pole Available | Yes (15A–125A) | Limited (QT2020) |
| AFCI Available | Yes (QAF2) | No |
| GFCI Available | Yes | No |
| Panel Slot Restrictions | Any slot | Tandem-rated slots only |
| Typical Price | $5–$12 | $12–$18 |
| Code Compliance | Always allowed | Only in rated positions |
| Use Case | Standard circuits | Panel space expansion |
What Is a Tandem Breaker?
A tandem breaker (also called a twin, duplex, or cheater breaker) puts two independent single-pole circuits into the space of one standard breaker. Each half of the QT has its own trip mechanism and protects its own circuit independently. A QT1515 provides two 15A circuits in one slot. A QT2020 provides two 20A circuits. A QT1520 provides one 15A and one 20A circuit. They do NOT provide 240V — each half is on the same phase leg.
When Can You Use QT Tandems?
You can ONLY install QT tandem breakers in panel positions specifically rated for tandems. Your panel's circuit directory (the label inside the panel door) will show which positions accept tandems — typically marked with a small icon or noted in the legend. Installing tandems in non-rated positions is a code violation (NEC 408.54) and may not trip properly under fault conditions. Common Siemens panels allow tandems in the bottom 4–8 positions only.
When to Choose QP (Standard)
Use standard QP breakers for: all new panel installations where you have available slots, any circuit requiring AFCI or GFCI protection (tandems don't offer these), circuits over 30A, 2-pole 240V circuits (dryers, ranges, A/C units, water heaters), and any panel position not rated for tandems. QP is always the default choice — only use QT when you've run out of panel space.
When to Choose QT (Tandem)
Use QT tandem breakers when: your panel is completely full and you need additional 120V circuits, the panel positions you're using are rated for tandems (check the directory), the circuits are 30A or under, and the circuits don't require AFCI or GFCI protection. Common scenarios include adding lighting circuits, receptacle circuits for a basement finish, or circuits for a home addition when the panel has no empty slots.
The 'Cheater Breaker' Myth
QT tandems are sometimes called 'cheater breakers' because they were historically used to bypass panel capacity limits. When installed in rated positions, tandems are 100% code-compliant and safe. The problem arises when they're installed in non-rated positions or when a panel exceeds its maximum circuit count. Always verify your panel's tandem capacity before installation.
Verdict
QP is the standard choice for all normal installations. QT tandems are a legitimate solution for expanding panel capacity when you've run out of slots — but ONLY in tandem-rated positions. If you need AFCI, GFCI, 240V, or circuits over 30A, you must use QP. If you're constantly running out of panel space, consider upgrading to a larger panel rather than filling every slot with tandems.
Frequently Asked Questions
Can I put a QT tandem breaker in any slot?
No. QT tandems can only go in panel positions specifically rated for tandem breakers. Check your panel's circuit directory label to see which positions accept tandems. Installing in non-rated positions is a code violation.
Is a tandem breaker the same as a 2-pole breaker?
No. A tandem breaker provides two independent 120V circuits in one slot. A 2-pole breaker provides one 240V circuit across two slots. They serve completely different purposes.
Can I get AFCI protection with a QT tandem?
No. Siemens does not make AFCI tandem breakers. If your circuit requires AFCI protection (bedrooms per NEC 210.12), you must use a standard QP AFCI breaker (QAF2 series) in a full-size slot.
How many tandem breakers can I put in my panel?
Check your panel's circuit directory — it specifies exactly which positions accept tandems and the maximum number allowed. Exceeding the rated tandem count is a code violation even if the breakers physically fit.