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Siemens KM3B125 Molded Case Circuit Breaker
- 125A
- 3 Pole
- Bolt-On
Siemens
KM3B125
Molded Case Circuit Breaker
Brand
Siemens
SKU
KM3B125
Quantity
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Siemens KM3B125 - 125A 3 Pole Molded Case Circuit Breaker
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Description
Engineered for commercial applications, the Siemens KM3B125 is a 3-pole, 125A molded case circuit breaker. It provides reliable thermal magnetic protection with long-time and instantaneous trip functions for robust power distribution. This bolt-on MCCB installs into Siemens P4, P5, S4, and S5 panelboards, plus SB switchboards. As a legacy component, it is replaced by the HED63B125 using a mounting kit. Rated for 600VAC, the unit handles fault currents up to 65kA at 240V and 50kA at 480V.Specifications
| Brand | Siemens |
|---|---|
| Part Number | KM3B125-R |
| Series | KM |
| Amperage | 125A |
| Poles | 3 |
| Mounting Style | Bolt-On |
| Voltage | 600VAC |
| Phase | 3 |
| AIC Rating | 65kA @ 240VAC, 50kA @ 480VAC, 22kA @ 600VAC |
| Terminal Type | Lugs |
|---|---|
| For Use With | Siemens P4, P5, S4, S5 Panelboards, SB1, SB2, SB3 Switchboards, Motor Control Centers |
| Wire Gauge | 1 AWG - 500 kcmil (Cu/Al) |
| Max Wire | 500 kcmil |
| Min Wire | 1 AWG |
| Trip Technology | Thermal Magnetic |
|---|---|
| Trip Function Code | LI |
| Trip Function | Long-Time, Instantaneous |
| Trip Adjustability | Fixed Thermal, Adjustable Magnetic |
| Available Options | Shunt Trip, Auxiliary Switch, Undervoltage Release, Alarm Switch |
|---|---|
| Accessories | Load Side Lugs Included |
| Standards | UL 489, CSA C22.2 No. 5 |
| Approval | CSA, UL |
| Temp Rating | 40C |
| Construction Features | Interchangeable Trip Unit, Trip-Free Mechanism, HACR Rated |
Product FAQs
7 answersWhat is the recommended replacement for the legacy KM3B125 breaker?
The KM3B125 is a legacy component. Siemens recommends the HED63B125 as a functional substitute, though it requires a separate mounting kit to retrofit into existing P4, P5, S4, or S5 panelboards.
Which Siemens distribution equipment is compatible with this breaker?
The KM3B125 is a bolt-on breaker designed for integration into Siemens P4, P5, S4, and S5 panelboards. It is also compatible with SB1, SB2, and SB3 switchboards and select motor control centers.
What wire sizes and materials are supported by the terminals on this breaker?
The load side lugs accept either copper or aluminum conductors ranging from 1 AWG up to 500 kcmil.
How does the trip adjustability work on the KM3B125?
This breaker utilizes a thermal-magnetic trip unit with a fixed thermal element for long-time overload protection and an adjustable magnetic element, allowing you to fine-tune the instantaneous short-circuit response.
Is the KM3B125 suitable for HVAC equipment?
Yes, this breaker is HACR rated, making it suitable for use with heating, air conditioning, and refrigeration equipment. It also features a trip-free mechanism to ensure the breaker trips even if the handle is held in the ON position.
What internal accessories can be installed in the KM3B125 frame?
This molded case circuit breaker supports field-installable accessories, including shunt trips, auxiliary switches, undervoltage releases, and alarm switches for remote monitoring and control.
Can the trip unit on the KM3B125 be swapped out?
Yes, the KM3B125 is built with an interchangeable trip unit, allowing the thermal-magnetic trip assembly to be changed if different protection characteristics are required for the application.
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