Square D A1B390 Molded Case Circuit Breaker
- 90A
- 3 Pole
- Bolt-On
Quantity
Square D A1B390 - 90A 3 Pole Molded Case Circuit Breaker
Re-Certified
Quantity
Description
Designed for older commercial and industrial installations, this 90A molded case circuit breaker delivers dependable thermal-magnetic overcurrent protection. The three-pole unit features a bolt-on mounting style engineered exclusively for legacy Square D NA1B panelboards. Operating at 240VAC with a 10kAIC interrupt rating, it includes a distinctive long body construction. A built-in Visi-Trip indicator allows facility managers to easily spot tripped circuits during maintenance.Specifications
| Brand | Square D |
|---|---|
| Part Number | A1B390-R |
| Series | A1B |
| Amperage | 90A |
| Poles | 3 |
| Mounting Style | Bolt-On |
| Voltage | 240VAC |
| Phase | 3 |
| AIC Rating | 10kA @ 240VAC |
| Terminal Type | Lugs |
|---|---|
| For Use With | Square D NA1B Panelboards |
| Wire Gauge | 4-1/0 AWG (Cu/Al) |
| Max Wire | 1/0 AWG |
| Min Wire | 4 AWG |
| Trip Technology | Thermal Magnetic |
|---|---|
| Trip Function Code | LI |
| Trip Function | Long-Time, Instantaneous |
| Trip Adjustability | Fixed Thermal, Fixed Magnetic |
| Accessories | Load Side Lugs Included |
|---|---|
| Standards | CSA C22.2 No. 5, UL 489 |
| Approval | CSA, UL |
| Temp Rating | 40C |
| Construction Features | Visual Trip Indicator, Long Body |
Product FAQs
7 answersWhat panelboards accept the Square D A1B390 circuit breaker?
This breaker is specifically engineered to mount into legacy Square D NA1B panelboards, which are commonly found in older commercial and industrial distribution systems.
Is the A1B390 a current production model from Square D?
No, the A1B series is an obsolete product line. It is primarily sourced to maintain, repair, or expand existing electrical systems that utilize legacy NA1B load centers.
Does the A1B390 require special mounting hardware for installation?
Because it is a bolt-on breaker designed for vintage NA1B panelboards, it fastens directly to the bus. Ensure you have the correct bus connection hardware, as legacy panelboards may require specific phase connectors if the original hardware is missing or damaged.
Can the A1B390 be used to replace a breaker in a standard QO or NQOD panelboard?
No, the A1B frame has a unique physical footprint and bolt-on configuration that is not interchangeable with standard QO, QOB, or NQOD series breakers. It must only be installed in compatible NA1B enclosures.
What does the LI trip function code mean on this breaker?
The LI designation indicates a thermal-magnetic trip unit providing Long-Time (L) protection for sustained overloads and Instantaneous (I) protection for immediate short-circuit clearing. Both the thermal and magnetic trip points are fixed on this model.
Is the 10kAIC rating sufficient for modern commercial installations?
A 10kA interrupting capacity at 240VAC was standard for many legacy systems, but modern commercial fault current requirements often exceed this. An electrician or engineer must verify the available fault current at the panel before installing this breaker to ensure it meets current safety codes.
What type of conductors can be terminated on the A1B390 lugs?
The factory lugs are dual-rated for either copper or aluminum wiring, accepting conductor sizes from 4 AWG up to 1/0 AWG. Always torque terminals to the manufacturer specifications marked on the breaker.
SuperClub
Join free. Get 500 SuperPoints.
Earn points on eligible purchases and redeem them at checkout.
100 SuperPoints = $1 off.
Warranties
Add an extra year of protection
60-Day Warranty
Your purchase includes 60 days of SuperBreakers warranty coverage.
Add a 1-year warranty extension in your cart.
Get a Quote
Don’t see what you’re looking for?
We source obsolete and hard-to-find parts every day.
Shipping
Free Shipping Policy
Parcel shipments with item value over $99 qualify for free economy shipping within the continental US. Please call to confirm special handling instructions. We do not charge a handling fee or require a minimum amount on any order. SuperBreakers does not ship on customer accounts.
Same Day Shipping
We strive to ship out your items the same day the order is placed. In rare circumstances SuperBreakers may reserve up to 5 business days to consolidate orders for complete shipment.
Expedited Shipments
Orders being shipped via Next Day Air, 2 Day Shipping or 3 Day Shipping must be received by 3 PM EST to guarantee same-day shipments. Expedited orders only ship on normal business days. Shipments will NOT be sent out on Saturdays and Sundays.
International Shipping
All International orders require a $1,000 minimum order threshold. Due to the special nature of these shipments, we require that these be placed with a SuperBreakers representative. Additional shipping and instructions will apply. All International Orders are Non-Cancel and Non-Refundable.
Reviews
Review summary
Customers rate this product 5.0 out of 5 based on 2 reviews.
- NLNoble L.ReviewingSquare D A1B115 - 15A 1 Pole Molded Case Circuit BreakerI recommend this productRated 5 out of 5 stars7/19/21Great Service, On Time Delivery, Great Price
SuperBreakers is my a dependable source to meet my customer's requirements at a good value and with on time delivery. When you throw in great customer service, you can't beat that combination.
- CHCobe H.ReviewingSquare D A1B120 - 20A 1 Pole Molded Case Circuit BreakerI recommend this productRated 5 out of 5 stars2/11/19Repeat customer
Although these breakers are refurbished they work great. It beats having to change the whole panel because of one breaker.