Square D MH320 Miniature Circuit Breaker
- 20A
- 3 Pole
- Bolt-On
Quantity
Square D MH320 - 20A 3 Pole Miniature Circuit Breaker
Re-Certified
Quantity
Quantity
Square D MH320 - 20A 3 Pole Miniature Circuit Breaker
New
Quantity
| Brand | Square D |
|---|---|
| Part Number | MH320 |
| Series | MH |
| Amperage | 20A |
| Poles | 3 |
| Mounting Style | Bolt-On |
| Voltage | 240VAC |
| Phase | 3 |
| AIC Rating | 10kA @ 240VAC |
| Terminal Type | Box Lugs |
|---|---|
| For Use With | Legacy Square D MH Panelboards |
| Wire Gauge | 14-8 AWG (Al/Cu) |
| Max Wire | 8 AWG |
| Min Wire | 14 AWG |
| Trip Technology | Thermal Magnetic |
|---|---|
| Trip Function Code | LI |
| Trip Function | Long-Time, Instantaneous |
| Trip Adjustability | Fixed |
| Accessories | Load Side Lugs Included |
|---|---|
| Standards | UL 489, CSA C22.2 No. 5 |
| Approval | UL |
| Temp Rating | 40C |
| Construction Features | Visual Trip Indicator |
Quantity
Square D MH320 - 20A 3 Pole Miniature Circuit Breaker
Re-Certified
Quantity
| Brand | Square D |
|---|---|
| Part Number | MH320-R |
| Series | MH |
| Amperage | 20A |
| Poles | 3 |
| Mounting Style | Bolt-On |
| Voltage | 240VAC |
| Phase | 3 |
| AIC Rating | 10kA @ 240VAC |
| Terminal Type | Box Lugs |
|---|---|
| For Use With | Legacy Square D MH Panelboards |
| Wire Gauge | 14-8 AWG (Al/Cu) |
| Max Wire | 8 AWG |
| Min Wire | 14 AWG |
| Trip Technology | Thermal Magnetic |
|---|---|
| Trip Function Code | LI |
| Trip Function | Long-Time, Instantaneous |
| Trip Adjustability | Fixed |
| Accessories | Load Side Lugs Included |
|---|---|
| Standards | UL 489, CSA C22.2 No. 5 |
| Approval | UL |
| Temp Rating | 40C |
| Construction Features | Visual Trip Indicator |
Description
Providing essential overcurrent protection, this 20-amp miniature breaker handles three-phase commercial loads. The unit utilizes proven thermal-magnetic trip technology to safeguard wiring against overloads and short circuits in demanding environments. Installs into legacy Square D MH panelboards to keep existing distribution systems operational. Facility engineers can also use the QOB320 as a verified substitute when replacing components in these specific older enclosures.Specifications
| Brand | Square D |
|---|---|
| Part Number | MH320-R |
| Series | MH |
| Amperage | 20A |
| Poles | 3 |
| Mounting Style | Bolt-On |
| Voltage | 240VAC |
| Phase | 3 |
| AIC Rating | 10kA @ 240VAC |
| Terminal Type | Box Lugs |
|---|---|
| For Use With | Legacy Square D MH Panelboards |
| Wire Gauge | 14-8 AWG (Al/Cu) |
| Max Wire | 8 AWG |
| Min Wire | 14 AWG |
| Trip Technology | Thermal Magnetic |
|---|---|
| Trip Function Code | LI |
| Trip Function | Long-Time, Instantaneous |
| Trip Adjustability | Fixed |
| Accessories | Load Side Lugs Included |
|---|---|
| Standards | UL 489, CSA C22.2 No. 5 |
| Approval | UL |
| Temp Rating | 40C |
| Construction Features | Visual Trip Indicator |
Product FAQs
7 answersCan I install the MH320 in a standard Square D QO or NQ panelboard?
No, the MH320 is a legacy M-frame molded case circuit breaker designed exclusively for older Square D MH panelboards. It will not fit in modern QO, NQ, or I-Line enclosures.
How is the MH320 secured inside the panelboard?
This breaker uses a bolt-on mounting configuration, requiring it to be mechanically fastened directly to the panelboard bus. This provides a secure, high-vibration-resistant connection compared to plug-on alternatives.
What are the wiring requirements for the box lugs on this breaker?
The terminal lugs are rated for both aluminum and copper conductors, accepting wire sizes from 14 AWG up to 8 AWG. Always ensure proper torque specifications are followed during installation to prevent thermal issues.
How does the thermal-magnetic trip unit in the MH320 function?
The fixed thermal-magnetic mechanism provides dual-level protection. The thermal component (long-time) responds to gradual overloads by heating a bimetallic strip, while the magnetic component (instantaneous) trips immediately in the event of a severe short circuit.
Are MH320 breakers still available for legacy panel maintenance?
Yes, while the original Square D MH panelboards are obsolete, replacement breakers like the MH320 remain available to safely maintain and extend the operational life of existing distribution systems without requiring a full panel upgrade.
Can the MH320 be used in 480V distribution systems?
No, this breaker is strictly rated for a maximum of 240VAC. It is typically deployed in 208Y/120V or standard 240V three-phase applications and is not rated for 480V or 600V equipment.
Is the MH320 suitable for high fault current applications?
With a maximum interrupting rating of 10kA at 240VAC, this breaker is intended for standard commercial applications. It must not be installed in systems where the available fault current exceeds 10,000 amps.
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Reviews
Review summary
Customers rate this product 5.0 out of 5 based on 4 reviews.
- DLDeanna L.Verified BuyerReviewingSquare D MH36800 - 800A 3 Pole Molded Case Circuit BreakerI recommend this productRated 5 out of 5 stars8/11/26Square D MH36800 - 800A 3 Pole Molded Case Circuit Breaker
Another satisfied customer.
- SBSteve B.Verified BuyerReviewingSquare D MH36600 - 600A 3 Pole Molded Case Circuit BreakerI recommend this productRated 5 out of 5 stars1/23/26Square MH36600
Breaker was as advertised excellent condition
- SAStewart A.ReviewingSquare D MH38 Panel Board EnclosureI recommend this productRated 5 out of 5 stars3/25/19not at local supply
got what I needed, because it was not available at my local supply house.
- WWWilliam W.ReviewingSquare D MH32 Panel Board EnclosureI recommend this productRated 5 out of 5 stars7/1/18INSIDE THE BOX
Great Buy ! Shipped on time. No Damage. Just what we ordered Thanks