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Square D QOB390-1021 Miniature Circuit Breaker
- 90A
- 3 Pole
- Bolt-On
Square D
QOB390-1021
Miniature Circuit Breaker
Brand
Square D
SKU
QOB390-1021
Quantity
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Square D QOB390-1021 - 90A 3 Pole Miniature Circuit Breaker
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Description
Rated for 10kAIC at 240VAC, this 90-amp miniature circuit breaker includes a factory-installed shunt trip accessory. The 120/208/240VAC shunt trip enables remote tripping via a separate control circuit. This three-pole unit mounts into Square D NQ and NQOD panelboards. Due to the added shunt trip module, the breaker requires four panel spaces instead of three. It features a Visi-Trip indicator that clearly shows when the breaker has tripped, alongside standard thermal-magnetic protection.Specifications
| Brand | Square D |
|---|---|
| Part Number | QOB390-1021 |
| Series | QOB |
| Amperage | 90A |
| Poles | 3 |
| Mounting Style | Bolt-On |
| Voltage | 240VAC, 120/240VAC, 48VDC |
| Phase | 3 |
| AIC Rating | 10kA @ 240VAC, 10kA @ 120/240VAC, 5kA @ 48VDC |
| Frame Type | QO |
|---|---|
| Terminal Type | Box Lugs |
| For Use With | NQ Panelboards, NQOD Panelboards |
| Wire Gauge | 4 AWG - 2/0 AWG (Al/Cu) |
| Max Wire | 2/0 AWG |
| Min Wire | 4 AWG |
| Trip Technology | Thermal Magnetic |
|---|---|
| Trip Function Code | LI |
| Trip Function | Long-Time, Instantaneous |
| Trip Adjustability | Fixed |
| Available Options | Auxiliary Switch, Alarm Switch, Padlock Attachment |
|---|---|
| Accessories | Load Side Lugs Included, Shunt Trip (Factory Installed) |
| Standards | CSA C22.2 No. 5, UL 489, HACR |
| Approval | CSA, HACR, UL |
| Temp Rating | 40C |
| Construction Features | Visual Trip Indicator, HACR Rated, Common Trip, Non-Interchangeable Trip, Quick-Make/Quick-Break, Trip-Free Mechanism |
Product FAQs
11 answersWhat does the "-1021" suffix mean on the QOB390-1021?
The "-1021" suffix indicates that this circuit breaker includes a factory-installed 120/208/240VAC shunt trip accessory. This allows the breaker to be tripped remotely via a separate control signal.
How many panel spaces does the QOB390-1021 require?
Because it includes a factory-installed shunt trip accessory, this 3-pole breaker requires four panel spaces in your NQ or NQOD panelboard.
Which panelboards are compatible with the QOB390-1021?
This bolt-on miniature circuit breaker is designed exclusively for use in Square D NQ and NQOD panelboards. It will not fit in standard QO load centers, which require plug-on breakers.
Can I field-install a shunt trip on a standard QOB390 breaker instead of buying the QOB390-1021?
No, Square D miniature circuit breaker accessories like the shunt trip must be factory-installed. You cannot add a shunt trip to a standard QOB390 in the field.
What is the difference between QO and QOB breakers?
QO breakers are plug-on units designed for standard load centers, while QOB breakers like the QOB390-1021 feature a bolt-on mounting style. Bolt-on breakers are typically used in commercial and industrial panelboards to ensure a secure connection that will not vibrate loose.
Can I use aluminum wire with this 90A breaker?
Yes, the box lugs on the QOB390-1021 accept both aluminum and copper conductors ranging from 4 AWG to 2/0 AWG.
Does this breaker have a visual trip indicator?
Yes, it features the Square D Visi-Trip indicator. When the breaker trips, the handle moves to a center position and a red indicator appears in a window on the case, making it easy to identify the tripped circuit.
What is the interrupting capacity of the QOB390-1021 on DC systems?
While it is rated for 10kAIC at 120/240VAC, this breaker also carries a 5kAIC interrupting rating when used on 48VDC systems.
What does the "LI" trip function code mean?
The "LI" code indicates that the breaker uses a thermal-magnetic trip unit with Long-Time and Instantaneous protection. The Long-Time function protects against sustained overloads, while the Instantaneous function trips the breaker immediately during a short circuit.
Is the trip point adjustable on this 90A breaker?
No, the QOB390-1021 features a fixed thermal-magnetic trip unit. Neither the Long-Time overload nor the Instantaneous short-circuit trip settings can be adjusted in the field.
Can I use this breaker in a 3-phase system?
Yes, this is a 3-pole circuit breaker designed for use in 3-phase electrical systems. It provides protection across all three phases simultaneously.
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Reviews
Review summary
Customers rate this product 4.9 out of 5 based on 211 reviews.
Reviews Summary
Generated by AI from 100 most recent customer reviews
Last updated 3/11/26
Customers say these electrical breakers arrive exactly as ordered and work perfectly for their intended applications. They consistently praise the competitive pricing, which many report is significantly lower than local suppliers. Fast shipping and prompt delivery are frequently highlighted, with many receiving orders within days or even next-day delivery for urgent needs. The breakers arrive well-packaged and in excellent condition. Many reviews emphasize the company's extensive inventory availability, particularly for hard-to-find breakers. One customer experienced difficulty with order cancellation and was charged a restocking fee, which caused dissatisfaction.
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Rating
211 reviews
- MLMike L.Verified BuyerReviewingSquare D QOB250 - 50A 2 Pole Miniature Circuit BreakerI recommend this productRated 5 out of 5 stars10/9/26breaker orders
Breaker worked out great
Can not be happier with the quick shipping
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Thank you for getting me the breaker in a timely fashion
- DSDarren S.Verified BuyerReviewingSquare D QOB250 - 50A 2 Pole Miniature Circuit BreakerI recommend this productRated 5 out of 5 stars10/5/26Airport taxi lighting
After contactor replacement we discovered bad breakers and were able to get replacements from Super Breakers in 2 days. THANK YOU SUPER BREAKERS..
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Excellent product and service
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Excellent product and service