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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.

How it compares

Measured against everything we stock in Breakers & Circuit Protection, at today’s prices. Recalculated every night.

Price $108.99
Pricier than about 71% of the 1,135 comparable items (median $54.99).

Specifications

Product
Brand nameSIEMENS

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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