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Grey Siemens BQ2B040 two-pole bolt-on breaker, toggle switch, lug terminals

SIEMENS

SIEMENS BQ2B040 Circuit Breaker 40A 2 Pole 120/240V AC

SKU CH-C8NS-1R7SG

A 40 A, two-pole miniature circuit breaker rated 120/240 V AC with 10 kA interrupting capacity for Siemens bolt-on panelboards

  • Protects circuits up to 40 A with 10 kA interrupting rating
  • Fits standard Siemens panelboards using bolt-on mounting
  • Operates reliably up to 104 °F ambient temperature
  • Compact 3.7 × 4.5 × 12.8 in frame saves panel space
  • Accepts wire down to 8 AWG for secure connections

Application and Audience

This Siemens BQ-series miniature circuit breaker is rated at 40 amps and two poles for 120/240 V AC single-phase panels. It fits Siemens panelboards that accept bolt-on mounting and is intended for installers protecting branch circuits up to the 125 A frame limit.

Interrupting Capacity

The decisive specification is the 10 kA AIR rating at 120/240 V AC, which defines the maximum prospective fault current the device can safely interrupt. If the available short-circuit current at the panel exceeds this value, a breaker with a higher AIR rating must be selected instead.

Sustained Load Behaviour

The breaker carries 40 A continuously within its 104 °F maximum operating temperature when wired with conductors of at least 8 AWG to the lug terminals. Thermal tripping responds to prolonged overcurrent rather than momentary peaks, so the device remains closed during normal inrush but opens on persistent overloads.

Highlights

  • Protects circuits up to 40 A with 10 kA interrupting rating
  • Fits standard Siemens panelboards using bolt-on mounting
  • Operates reliably up to 104 °F ambient temperature
  • Compact 3.7 × 4.5 × 12.8 in frame saves panel space
  • Accepts wire down to 8 AWG for secure connections

Specifications

BrandSIEMENS

Questions about this item

What does the 40 A rating mean when the breaker is installed in a panel?

It will carry up to 40 A continuously and trip on overloads or short circuits to protect the downstream wiring.

How does the 10 kA AIR rating at 120/240 V AC limit the breaker's use?

It caps the maximum prospective fault current the breaker can safely interrupt at 10 000 A on a 120/240 V AC system.

What panel space and mounting style does the BQ frame require?

The bolt-on BQ frame occupies two poles in a compatible Siemens panelboard and measures 3.7 in long, 4.5 in wide and 12.8 in deep.

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