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Square D QOB140 miniature circuit breaker, single-pole paddle actuator, bolt-on mounting, light grey plastic body

SQUARE D

SQUARE D QOB140 Miniature Circuit Breaker 40A 1 Pole 120/240V AC

SKU CH-AQF5-R7VAB

Protects single-phase 120/240 V AC circuits up to 40 A with a 10 kA interrupt rating in a bolt-on QO frame

  • 40 A single-pole protection for 120/240 V AC circuits
  • 10 kA interrupting rating handles high fault currents
  • Bolt-on mounting fits Square D QO load centres
  • 48 V DC rating adds low-voltage versatility
  • Compact 3.1 × .8 × 2.9 in frame saves panel space

Square D QOB140 40 A bolt-on breaker

The Square D QOB140 is a single-pole miniature circuit breaker rated at 40 A and 120/240 V AC. It uses the QO bolt-on mounting style and fits Square D NQOD panelboards. The device carries a 10 kA interrupting rating at the rated voltage. It also supports 48 V DC circuits.

Thermals noise and power draw

The breaker operates within a minimum temperature of 77 °F. As a passive protection device it generates no audible noise and draws no operating power. Thermal-tripping action responds to sustained over-current without external energy. The paddle actuator provides manual switching.

Deciding specification

The bolt-on QO mounting style is the single specification that determines compatibility. Only panelboards designed for QO bolt-on breakers will accept this unit. Buyers with plug-on or DIN-rail panels cannot use it.

How it compares

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

Price $27.99
Cheaper than about 72% of the 1,135 comparable items (median $54.99).

Specifications

Product
Brand nameSQUARE D

Questions about this item

How do I bolt this QOB140 breaker onto the panel rail, and what step is often missed?

Align the bolt-on foot with the QO panel rail, tighten the mounting screw securely, then snap the paddle actuator down until it locks; the step often missed is fully tightening the mounting screw before energising the panel.

What maintenance or replacement will this 40 A single-pole breaker need over time?

Periodically torque the lug terminal to the manufacturer value, exercise the paddle actuator annually, and replace the breaker if it trips at or below 40 A during a calibrated test or shows discoloration at the lug.

What limit appears first when this breaker runs continuously near 40 A in a 77 °F ambient?

The thermal element will reach its trip curve first; sustained current at 40 A in 77 °F ambient causes the breaker to open on its inverse-time characteristic before the 10 kA interrupting rating or 120/240 V AC voltage rating becomes a factor.

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